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Defects in Masonry
Walls
Guidance on Cracking:
Identification,
Prevention and Repair
Publication 403
CIB W023 – Wall Structures
Defects in Masonry Walls.
Guidance on Cracking: Identification,
Prevention and Repair
Coordination
Hipólito Sousa, Portugal
Authors
Ercio Thomaz, Brazil
Hipólito Sousa, Portugal
Humberto Roman, Brazil
John Morton, UK
José M. Silva, Portugal
Márcio Corrêa, Brazil
Oscar Pfeffermann, Belgium
Paulo B. Lourenço, Portugal
Romeu S. Vicente, Portugal
Rui Sousa, Portugal
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
Table of Contents
Presentation ..................................................................................................................... 1
Preface ............................................................................................................................. 3
1- Introduction .................................................................................................................. 5
1.1-
M
OTIVATION
........................................................................................................ 5
1.2-
M
AIN OBJECTIVES
................................................................................................ 7
1.3-
O
RGANIZATION
.................................................................................................... 7
2- Specifics of Masonry Walls and Identification of Defects
,
........................................ 9
2.1-
B
UILDING MASONRY SOLUTIONS
............................................................................ 9
2.2-
D
EFECTS IN MASONRY WALLS
............................................................................. 13
2.2.1- General aspects ........................................................................................ 13
2.2.2- Identification of Masonry cracking .............................................................. 17
3- Prevention of Cracking in Masonry Walls ................................................................ 23
3.1-
G
ENERAL CAUSE OF CRACKING
.......................................................................... 23
3.2-
I
MPROVEMENT IN SERVICEABILITY BEHAVIOUR
,,
................................................... 25
3.2.1- Codes and design criteria .......................................................................... 25
3.2.2- Detailing aspects of movements and joints ............................................... 28
3.2.3- Permissible deviations and tolerances ...................................................... 35
3.3-
C
RACKING PREVENTION IN MASONRY PARTITION WALLS
....................................... 37
3.3.1- General ..................................................................................................... 37
3.3.2- Origin of defects in interior walls (partitions) .............................................. 37
3.3.3- Prevention of cracks .................................................................................. 42
3.3.4- Calculation of the deflection ....................................................................... 44
3.3.5- Limitation of the deflection ......................................................................... 44
3.3.6- Practical means to protect partitions from cracking .................................... 44
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
3.4-
C
LADDING CRACKING IN
UK
AND
I
RELAND
........................................................... 47
3.5-
B
RAZILIAN
S
TANDARDS FOR
P
REVENTION OF
C
RACKING IN
M
ASONRY
,,
................. 51
3.5.1- Introduction ................................................................................................ 51
3.5.2- Masonry deformability................................................................................ 51
3.5.3- Limits for dimensions and cuts in masonry ................................................ 52
3.5.4- Control and movement joints ..................................................................... 53
3.5.5- Deflection limits ......................................................................................... 53
3.5.6- Observations regarding reinforced concrete structures .............................. 54
3.5.7- IPT Recommendations .............................................................................. 54
4- Repair Strategies for Cracking in Masonry Walls ................................................... 59
4.1-
P
ROBLEM ASSESSMENT AND STRATEGIES
........................................................... 59
4.2-
B
RAZILIAN CRACKING REPAIR TECHNIQUES
,,
......................................................... 62
4.2.1- Introduction ................................................................................................ 62
4.2.2- Prevention and repair ................................................................................ 63
4.2.3- Repair Methods ......................................................................................... 70
4.2.4- Case study ................................................................................................ 70
4.2.5- Remarks .................................................................................................... 72
5- Conclusions and Guidance to Prevent and Repair Cracking in Masonry Walls... 75
5.1-
G
ENERAL
R
EMARKS
........................................................................................... 75
5.2-
G
UIDANCE TO PREVENT CRACKING
...................................................................... 76
5.3-
R
EPAIR STRATEGIES
........................................................................................... 78
5.4-
RESEARCH NEEDS
.............................................................................................. 78
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
1
Presentation
Over the past decade the CIB Commission W023- Wall Structures has engaged in the
preparation of documents covering specific aspects of the construction of building wall
structures. To this end, a strategy of setting up working groups taking care of different
issues was designed.
Currently, the following working groups are acting within the Commission: WG1-
Serviceability of Masonry Walls, WG2- Preparation of Codes on Masonry, WG3- Large
Panel Buildings, WG4- Historic Masonry Buildings, WG5- Reinforced and Prestressed
Masonry, WG6- Seismic Design of Masonry Structures, and WG7- Complex Shaped
Masonry.
As a result of these actions, in 2006 a book was prepared by the Commission and
published by the publisher Taylor and Francis, entitled “Enclosure Masonry Wall
Systems Worldwide”, presenting the typical masonry wall enclosures in twelve
countries, representing different continents.
Later, in 2010, was published the “Guide on Structural Rehabilitation of Heritage
Buildings” which constitutes CIB Publication 335, with guidance for dealing with
interventions of rehabilitation of heritage buildings, with a special emphasis on the
assessment of the structural safety.
Now, in 2014, the Commission concluded the preparation of the document entitled
“Defects in Masonry Buildings. Guidance on Cracking: Identification, Prevention and
Repair”, focusing on preventing cracking defects in masonry walls.
Other publishing projects are underway: a publication entitled “Reinforced and
Prestressed Masonry”, covering all essential aspects of these specific types of masonry,
and a document entitled “Complex Shaped Masonry”, dedicated to the specific aspects
of the design of masonry elements of complex shape. It is expected to have these
documents finalised in the coming years.
The document “Defects in Masonry Buildings. Guidance on Cracking”, is focused on
emphasizing the importance of ensuring the proper serviceability behaviour of masonry
walls, in order to avoid defects, especially cracks, through: identifying the most
common types of cracking associated with the behaviour in service of masonry walls;
presentation of some strategies for crack repairs; presentation of some recommendations
and guidance to prevent and repair cracks in masonry walls; and, identifying research
needs, in order to improve the existing recommendations.
This document was developed under the coordination of Hipólito Sousa, Convenor of
WG1, by a Panel of Authors, members of CIB Commission W023 and other experts
with recognised curricula. Contributions were also received from other experts around
the world, with knowledge of the situation in their countries. Thanks are due to all of
them.
I hope that this publication will be fruitful and contribute to the development and the
progress in the quality of masonry, i.e. to perform masonry walls without defects,
specially, cracking.
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
2
After 18 years as the Coordinator, I am proud of the achievements made by the CIB
Commission W023 during this period.
I take the opportunity to thank the members of the Commission throughout this period
for their cooperation in the Commission activities. I also thank the CIB Secretariat, in
particular the Secretary-General Wim Bakens, for the cooperation and constant
encouragement, and the confidence expressed by the CIB Programme Committee,
notably by awarding the CIB PC Commendation 2006.
November 2014
S. Pompeu Santos
Coordinator of CIB Commission W023
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
W023
Wall Structures
3
Preface
CIB Commission W023 - Structural Walls is fundamentally concerned with masonry,
mainly with Codes, Historic Buildings and Seismic Design.
Important concerns have been raised, particularly about the serviceability behaviour of
masonry walls, structural or infilling, since it has been realised that there is a need to
pay more attention to these aspects, recognising their relation with defects on masonry
walls.
A working group: WG1- Serviceability of Masonry Walls was created in 2011 within
the Commission with the mission to prepare a guide focused on avoiding cracking
defects in masonry walls.
Considering the diversity of masonry uses, this guide was intended to be a concise
document, to have general interest and to complement the guidance in structural codes.
The objective is not to deal with the diagnosis of masonry defects, or with the defects
associated with seismic or ancient buildings, but to help technicians with its
identification, prevention and repair.
The document was prepared by a Panel of Authors, members of CIB Commission
W023 and other experts, under the Coordination of Hipólito Sousa, also Convenor of
WG1.
The authors are: Ercio Thomaz (Brazil), Hipólito Sousa (Portugal), Humberto Roman
(Brazil), John Morton (UK), José M. Silva (Portugal), Márcio Corrêa (Brazil), Oscar
Pfeffermann (Belgium), Paulo B. Lourenço (Portugal), Romeu S. Vicente (Portugal)
and Rui Sousa (Portugal).
Information about the masonry practices in their countries was also provided by the
following experts: Barry Haseltine (UK), Dirk Martens (Netherlands), Erhard Gunkler
(Germany), Jan Kubica (Poland), Oliver Dupont (France), Roberto Capozucca (Italy)
and Tor-Ulf Weck (Finland). A revision of the English language of the document was
made by John Morton (UK) and Barry Haseltine (UK).
The document was approved in general at the Commission meeting in Antwerp
(Belgium) in October 2014. It was subsequently subjected to minor adjustments and
brought to the attention of all members of the Commission and then published by the
CIB Secretariat.
To all those who have contributed selflessly to the preparation of this publication I
express my sincere thanks.
I sincerely hope that this document is an unpretentious but interesting contribution for
the growing knowledge in the masonry field.
November 2014
Hipólito Sousa
Coordinator of the Panel of Authors
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Introduction
W023
Wall Structures
4
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Introduction
W023
Wall Structures
5
1- Introduction
1,2,3,4
1.1-
M
OTIVATION
In recent years, CIB Commission W023- Wall Structures has been involved in the
preparation of background documents for design standards, building codes and
recommendations for masonry structures. Working groups were created in order to
develop specific aspects related to masonry behaviour, such as: Serviceability of
Masonry Walls, Preparation of Codes on Masonry, Historic Masonry Buildings,
Reinforced and Prestressed Masonry, Seismic Design of Masonry Structures or
Complex Shaped Masonry.
In this respect the present work has been developed by a working group dealing with the
serviceability behaviour of masonry walls, since the need to give more attention to these
aspects and their relation with defects in masonry walls was identified.
The concept of defects is quite subjective, because in building construction there is still
a strong component of manual work, where workmanship is very important.
This document is concerned with defects that are not simple, minor aesthetic,
imperceptible or unavoidable failures, but with failures that could be considered to
compromise the building behaviour and might result in a claim being made. Nowadays
masonry is still used in important structural and non-structural elements.
In many situations, as is usual in northern European countries, masonry is commonly
the structure in load-bearing masonry buildings. In other applications, such as is usual in
southern European countries, masonry is mainly used for infill walls in buildings with
reinforced concrete frames.
Figure 1.1 - Example of masonry wall with cracking
1
Hipólito Sousa – Portugal
2
Ercio Thomaz - Brazil
3
Márcio Corrêa - Brazil
4
Humberto Roman – Brazil
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Introduction
W023
Wall Structures
6
Theoretically the infilling walls have no relevant mechanical behaviour, but in practice
these walls have structural importance since some transference of loading can occur due
to building structure/wall interactions. These interactions, as well as other effects like
dimensional changes of the walls, due to thermal or moisture movements or foundation
settlement, can lead to several different defects in masonry walls in serviceability states,
such as cracking, one of the most important (Figure 1.1).
On the other hand, apart from the structural role, or not, of masonry walls, these
cracking defects can affect other important functional walls requirements.
According to Grimm [1.1], cracks are the first cause of three occurrences, as shown in
Figure 1.2. Besides the implications in Figure 1.2 there is also significant damage to
acoustic insulation, durability and the fire resistance of masonry.
Figure 1.2 - Problems related to cracks in masonry [1.1]
Moreover, despite the general quality improvement expected from the profusion of
codes and standards, in recent years some building masonry cracking defects are still
being reported with high frequency in different countries. These defects incur costs and
can involve litigation between different parties involved in the construction process. In
terms of liability, which party is responsible is a relevant question.
In fact, although building construction is an industrial activity, we know that buildings
are still prototypes and in some areas, like masonry, the relationship between traditional
technologies and local materials is relevant and important, so different practices evolve
in different areas.
Therefore, these aspects justify that more attention should be paid to design in order to
avoid or minimise defects associated to the serviceability behaviour on masonry walls,
whether structural or non-structural.
As underlined by Thomaz [1.2], crack prevention deals with any things such as those
shown in Figure 1.3.
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Introduction
W023
Wall Structures
7
Figure 1.3 - Crack prevention [1.2]
1.2-
M
AIN OBJECTIVES
Considering the motivation and the diversity of masonry solutions, this guide aims to be
a document which will be of general interest and will complement the guidance in
structural codes.
The objective is not to deal with the diagnosis of masonry defects, named by several
authors as “building pathology” [1.3], or with the defects associated with seismicity,
where a lot of research and methods are already available. Also this document is not
intended to be used for historic or ancient buildings.
So, focused on actual masonry buildings worldwide where there is information, the
main objectives of this guide are:
• to underline the importance of assuring good serviceability behaviour of
structural or infilling masonry walls so as to avoid defects, mainly cracking;
• to identify the most common types of masonry cracking associated with the
serviceability behaviour of masonry walls in buildings;
• to present some strategies for crack repairs;
• to give some recommendations and guidance to both prevent and repair cracking
in enclosure and partition masonry walls;
• to identify some needs for research in this area and to formulate better
recommendations.
1.3-
O
RGANIZATION
The guide is organized in five chapters. Each chapter was prepared with the contribution
of several authors, as acknowledged.
The current Chapter 1 is intended to give a better understanding of the scope, main
objectives and organization of the guide.
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Introduction
W023
Wall Structures
8
Chapter 2 is intended to give an overview of masonry construction techniques in
different countries, to discuss the general causes of buildings defects and the
methodology of analysis, with a focus on masonry cracking identification.
Chapter 3 is dedicated to masonry serviceability improvement. After a short review of
code guidance, special reference is made to movement and joint detailing and
permissible deviation and tolerances, and also to cracking prevention criteria of
masonry partition walls. This chapter presents also the specific problem of cladding
cracking in UK and Ireland, and the Brazilian code recommendations to prevent
cracking in structural masonry.
Chapter 4 deals with the presentation of repair strategies for cracking in masonry walls,
including some Brazilian repair techniques.
In Chapter 5 brief conclusions are presented, with general remarks together with some
guidance on helping to prevent cracking. In addition, some research needs are given.
References
[
1.1] GRIMM, C. (1997) - "Masonry Cracks: Cause, Prevention and Repair", Masonry
International, 10(3), pp. 66-76.
[1.2] THOMAZ, E. (1998) - “Prevention and Repair of Masonry Cracks”, Journal of
Construction Technology, 37, pp. 48-52.
[1.3] CIB (2013) - “A State-of-the-Art Report on Building Pathology”, V. P. Freitas
(ed), CIB W086, FEUP, LFC (ISBN 978-90-6363-082-9).
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
9
2- Specifics of Masonry Walls and Identification of Defects
1,2
2.1-
B
UILDING MASONRY SOLUTIONS
There is a large variety of masonry wall solutions (Fig.s 2.1 to 2.3) which depends
mainly on locally available materials, climate conditions, building technologies and
housing traditions, amongst others. Nowadays masonry can be used in buildings in
different situations, but actually mainly as structural vertical support walls, or as a non-
structural infilling component within a steel or concrete framed structure. In both cases,
in building construction, masonry can form the enclosure or the partitions. In those two
functions the requirements and the behaviour expected from the masonry are very
different, and in both the design and construction phase these differences will always be
present.
(a)
(b)
Fig. 2.1 - Some examples of different types of masonry in Africa: (a) Urban buildings in
masonry at Maghreb; (b) Popular rural masonry houses in north Mozambique.
1
Hipólito Sousa – Portugal
2
Rui Sousa – Portugal
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
10
(a) (b)
Fig. 2.2 - Examples of different types of masonry in South America: (a) Urban poor
quality housing in Venezuelan “favelas” and (b) Modern urban buildings in Brazil
(a) Italy (b) Netherlands
(c) Germany (d) UK
Fig. 2.3 - Examples of different types of masonry in Europe [Photos (a), (c) and (d)
taken from 2.1]
In view of variations in the previous photographs it is important to give a general
overview of the most common masonry solutions and materials used worldwide, to
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
11
understand better the influence of such solutions in the masonry behaviour and how
these practices can be related to the causes of cracking in masonry walls.
Nowadays, in the majority of countries masonry is not as common a structural building
solution as it was in the past. Nevertheless, structural masonry is more used in many
Central European Countries (e.g., Belgium, France, Germany and Netherlands),
especially in low rise buildings of one or two storeys. It is also used in many countries
around the world.
Forming the building enclosure in masonry is a very common solution worldwide:
single leaf or cavity walls are both frequently used. In Europe perhaps clay bricks or
blocks (perforated either vertically or horizontally) are the most common units used laid
in general purpose mortar laid in normal joints or in thin joints (thin layer mortar).
Other units, such as concrete blocks and bricks, are also widely used. In virtually all
developed countries there are requirements for the building’s thermal performance
which generally result in the use of thermal insulation layer/s. The general use of
ancillary components is not present in all countries.
In frequent cases the same materials and similar solutions can be used in structural or
non-structural enclosure masonry. Masonry partition walls are constructed with
different materials, but normally when the wall is only infilling, the wall is usually
slender and lighter.
(*) Type of construction, includes materials, arrangement and cavities
Figure 2.4 - Aspects associated to masonry wall solutions
Tables 2.1, 2.2 and 2.3 give an overview of the most common solutions used for
masonry and masonry materials nowadays. Traditional and ancient masonry solutions
are not analysed. Most of information is about Europe and the information is given by
country. When considering the worldwide (non-European) countries, only the Brazilian
situation is presented. These tables are based on existing references [2.2] and
contributions of experts from different countries. All information is presented for a
range of solutions for non-structural (enclosure and partitions walls) and structural
masonry (internal/external walls).
- Construction (*)
- Finishes
- Thermal insulation
- Watertightness
Masonry walls
Structural Non-structural
(infilling)
Partitions Enclosure Enclosure Partitions
- Construction (*)
- Finishes
- Acoustic insulation
- Construction (*)
- Finishes
- Thermal insulation
- Relation with structure
-
Watertightness
- Construction (*)
- Finishes
- Thermal insulation
- Acoustic insulation
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
12
Table 2.1 - Non-structural masonry: Solutions and materials for enclosure walls
Region
Countries
Building
structure
Type of
masonry
Walls
Masonry materials
Units Mortars Ancillary
Thermal insulation
layer
Reinforced Concrete
Steel
Timber
Single leaf
Cavity
Veneer
Clay Concrete
Calcium Silicate
General Purpose
Thin layer
Light-weight
Wall Ties
Joint reinforcement
Lintels
Exterior
Cavity
Interior
No insulation or large
units
Dense
Light-weight
Dense
Light-weight
Auto.Aerated
South Europe
Greece
F R R R F R R F R R R R F R R NF
R R R F R R
Italy
F NF
NF
NF
F R F F R NF
R R F NF
R R NF
F F F R NF
Portugal
F R R F F R NF
F NF
R R R F R R R R NF
NF
F R NF
Spain
F R R F F R NF
F NF
R R R F R R R R NF
NF
F R NF
Central Europe
Belgium
F NF
NF
NF
F F NF
F NF
F F F F F R F F F NF
F NF
NF
France
F R NF
F NF
F NF
F F NF
NF
R F F R NF
R F NF
NF
F NF
Germany
F R R F F R NF
1
F NF
1
F NF
F F NF
NF
F NF
FF FF F R R
Netherlands
F NF
NF
NF
F NF
F R NF
R R R F NF
R F R F NF
F R R
Poland
F R R F F NF
NF
F R NF
F NF
NF
F R F NF
F F NF
R R
North.
Europe
Finland
F R F R R F F R R R R R F R R F NF
NF
R F F R
UK
F F F R F R F R NF
NF
NF
F F R R F NF
F NF
F NF
R
Brazil
F F R F R NF
R F R F NF
NF
F R R NF
NF
NF
R R R F
1- If exterior thermal insulation layers are mounted on the wall
Contributions of experts F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Existing references [2.2] F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Unknown information
U
Table 2.2 - Non-structural masonry: Solutions and materials for partition walls
Region
Countries
Building structure
Type of
masonry
Masonry materials
Units Mortars Ancillary
Reinforced Concrete
Steel
Timber
Single leaf
Cavity
Clay Concrete
Calcium Silicate
General Purpose
Thin layer
Light-weight
Wall Ties
Joint reinforcement
Lintels
Dense
Light-weight
Dense
Light-weight
Auto.Aerated
South Europe
Greece U
U U U U U U U U U U U U U U U U
Italy
F NF NF F NF NF F R NF NF R F NF R R NF F
Portugal
F R R F NF R F F R R R F R R R R R
Spain
U U U U U U U U U U U U U U U U U
Central Europe
Belgium
F R R NF F NF F NF F F F F F R F F F
France
F R R F R NF F NF R F R F F R R R R
Germany
NF R NF F R R F R NF F F NF F R F R NF
Netherlands
F F NF F NF R R R R R F F F R R R F
Poland
F R R F NF NF F R NF F NF R F R NF NF F
North.
Europe
Finland
F R R NF R F R R R R NF F NF R R R R
UK
F F F F R R R F F F F F NF R R NF NF
Brazil
F F R F R NF F R F NF NF F R R R NF F
Contributions of experts F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Existing references [2.2] F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Unknown information
U
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
13
Table 2.3 - Structural masonry: Solutions and materials for external and internal walls
Region
Countries
Masonry walls Masonry materials
Structural Type Units Mortars Ancillary Thermal insulation
layer
Unreinforced
Reinforced
Confined
Single
Cavity
Clay Concrete
Calcium Silicate
General Purpose
Thin layer
Light-weight
Wall Ties
Joint
reinforcement
Lintels
Exterior
Cavity
Interior
No insulation or
large units
Dense
Light-weight
Dense
Light-weight
Auto.Aerated
South Europe
Greece
R R R R R R R R R R R R R R R R R R R R R
Italy
F NF NF F F F F NF NF R R F NF R NF NF F F F NF NF
Portugal
R R R R R R R R R R R R R R R R R R R R R
Spain
U U U U U U U U U U U U U U U U U U U U U
Central Europe
Belgium
R F R NF F NF F NF F F F F F R F F F NF F R R
France
F R R F NF NF F F NF NF R F F R NF R F NF NF F NF
Germany
F NF F F F NF
1
F NF
1
NF NF F F NF NF F NF F F NF R R
Netherl.
F R R F F R NF NF R R F F F R F NF F R NF R R
Poland
F NF R F NF NF F R NF F NF F F R NF NF F F NF R R
North.
Europe
Finland
R NF R R R R R F R NF R F NF R R R NF R F
2
NF R
UK
F R R NF F F R R NF NF NF F R R F R F R F R R
Brazil
F F R R R R F R F R NF F R R R NF F R R R F
1- If exterior thermal insulation layers are mounted on external walls; 2- Insulation often built in the concrete units;
Contributions of experts F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Existing references [2.2] F- Frequent
F
U-
Used, but not frequent
NF
R- Not used/ Rare
R
Unknown information
U
2.2-
D
EFECTS IN MASONRY WALLS
2.2.1- General aspects
Problems with the behaviour of buildings normally appear through the occurrence of
defects.
The behaviour of buildings is quite complex and involves aspects of material science
that sometimes are not well understood yet. Also, masonry is a subject which is not
taught in depth during Engineering and Architecture University courses. These aspects
increase the difficulty in accurately identifying defects in buildings elements and
determining the cause. In general terms, the main causes of defects are associated with
human and natural causes (Table 2.4).
Defects in Masonry Walls.
Guidance on Cracking: Identification, Prevention and Repair
Specificities of Masonry Walls and Defects Identification
W023
Wall Structures
14
Table 2.4 - General causes of defects in buildings [2.3]
Causes Type Agent
Human actions
Design
Improper calculation methods and errors,
insufficient technical information and level
of detailing, improper design assessment
(loads, local conditions, compatibility
between different functionally aspects…)
Execution
Use of bad quality materials, inadequately
qualified and experienced personnel,
inadequate execution control of construction
works, bad interpretation of the project
Utilization
No, or inadequate, maintenance procedures,
changes in the utilization, excessive
loading…
Disasters
Fire, explosion, impact, …
Natural actions
Physical
Wind and rain effects, snow, creep,
thermal/moisture movements, …
Chemical
Oxidation, carbonation, acid rain, salts…
Biological
Vegetation (roots, fungus,...), animals
(warms, insects,...)
Disasters
Seismic, cyclone, avalanche, flood, volcanic
eruption, …)
Some studies point out that the most common cause of defects is associated with
mistakes in the design process and with inadequate execution of construction works.
The quality of building materials and the absence or maintenance quality are less
frequently considered as the cause.
In the particular case of masonry walls, the defects are mainly caused by incompatibility
between the different functional demands, inadequate construction detailing and / or
inadequate execution of construction works. Moreover, the use of new architectural
trends (Figure 2.5) and the use of new materials whose behaviour may not be fully
understood can also increase the potential of buildings exhibiting defects.
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Figure 2.5 - Example of architectural language with some aspects like shape and colour
that increase the risk of defects
In addition to knowing the cause, it is also important to distinguish whether the defect is
structural or non-structural.
Structural defects affect the mechanical behaviour of the construction element. These
elements may perform other functions (e.g. structural walls can also perform acoustic
and thermal insulation, water-tightness and fire resistance functions). Moreover,
structural defects can also affect non-structural elements, therefore it is important to
understand and consider the interaction between these two types of element to prevent
the defects.
In general terms, the most common masonry structural defects are:
− cracking due to the settlement of foundations, excessive loading and deformations
(shear and flexural) and other effects (creep, shrinkage and thermal);
− local crushing due to high compressive loads;
− corrosion of metallic elements or chemical reactions.
And the most common masonry non-structural defects are:
− undesired changes in the physical properties of the materials due to the presence
of water/humidity (from the soil, construction works, precipitation, condensation,
hygroscopicity, accidental causes, …) thus affecting the durability, aesthetics
and the environmental conditions of the buildings or building elements;
− cracking in non-structural elements (e.g. partition walls and applied rendering
systems) due to the interaction with structural elements, thus making this defect
associated with the structural ones;
− ageing and degradation of the materials, in particular rendering systems, due to
continuous exposure in the environment, inadequate use or absence of
maintenance procedures;
− inadequate behaviour in other aspects (non-structural safety, environment comfort
conditions, energy consumption).
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When defects have occurred, repair solutions and strategies are very important. A
proper analysis to correctly identify the defect and determine the cause of its occurring
must be performed. Only then can a repair solution be advocated.
Given the complexity and diversity of defects, the existence of different constructive
elements and possible interactions between them, the existence of many specific repair
solutions is implied. Moreover the effectiveness of the repair solutions requires a sound
knowledge about such problems.
Some methods developed to organize information about defects are referenced by
different authors and can be very useful tools to summarise information and help in
analysis and decision making. Normally, each analysis, tries to make an objective
description of the defects, organize the causes/hypotheses (Figure 2.6), and in some
cases to propose specific methods of repair (Figure 2.7).
Figure 2.6 - Example of method for identifying defects in masonry walls [2.4]
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Figure 2.7 - Example of method for identifying and repair defects in masonry walls [2.5]
2.2.2- Identification of Masonry cracking
As previously mentioned, modern masonry walls have an important role in the
building’s behaviour and may perform several functions. The technical research
associated with the development of modern codes and standards for masonry has
resulted in a general positive improvement in the quality of masonry construction.
Nevertheless, some defects still occur in masonry walls during service conditions. The
main defect found in masonry is cracking in the walls and applied finishes. The repair
work associated with these defects is expensive and frequently may not be totally
successful. Obviously defects in masonry can be much influenced by workmanship
quality but other causes can also be present.
Cracking defects are the main subject of this guide, in particular cracking of masonry
walls in serviceably conditions. This defect is common in structural and in non-
structural elements, including applied finishes, although the causes may be different in
some cases.
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The main cracking defects in structural masonry seem to be associated with ground
movements (settlement of foundations or seismic events), although defects like
expansion/shrinkage of masonry materials or thermal movements can also occur.
Moreover, the brittle nature and low tensile strength makes masonry, in particular
unreinforced masonry, highly susceptible to cracking due to small movements.
Non-structural masonry, such as enclosure and partition walls, have important roles
which may include functional aspects such as aesthetics, acoustic and thermal
insulation, and water-tightness. Structural safety is normally assured by independent
structural elements - in particular reinforced concrete columns beams and slabs, in
which the infill masonry is built. Therefore, cracking defects in enclosure and partition
walls are frequently associated with incompatibility between structural components (e.g.
excessive deformation of concrete slabs or beams, aggravated by long term effects),
expansion/shrinkage of masonry materials (e.g. clay or cement based elements) and
thermal movements (masonry and building structure).
Also when rendering or other types of finishes are applied to the walls, in general the
same types of non-structural defects may occur. In the particular case of cracking, this
defect can be caused by the movements of the supporting walls and it can therefore be
associated with structural or non-structural defects. However, other types of cracking
defects not caused by the support walls can be found in rendering systems. These
defects are mainly caused by the nature of the rendering materials, the construction
choice and execution procedures (e.g. cracking due to shrinkage in mortars made from a
high quantity of hydraulic binders, too great a joint thickness or improper environmental
and/or execution conditions). Furthermore, if there are also unsuitable design details,
construction practices, or when special shaped units are not used where they should be
used, cracking defects in structural and in non-structural masonry can occur. The
absence of specific masonry units for particular construction situations and the reduced
use of ancillary components can also increase the propensity for cracking to occur,
figures 2.8 to 2.13 (Note:
the schematic drawings are intentionally exaggerated).
Figure 2.8 - Example of cracking in masonry due to differential settlement of
foundations [Photo taken from 2.6]
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Figure 2.9 - Example of cracking in masonry due to excessive deflection of the top slab
(probably, less rigid than the floor concrete slab)
Figure 2.10 - Example of cracking in masonry due to thermal movements of roof slabs
Figure 2.11 - Example of cracking in masonry due to moisture shrinkage
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Figure 2.12 - Example of cracking due to moisture expansion of masonry walls [Photo
taken from 2.7]
Figure 2.13 - Example of masonry cladding failing due to thermal/moisture movements
and insufficient connections (ties) to the support wall [Photo taken from 2.7]
In order to help to avoid these problems, technical applied knowledge, specifications
and detailing information should be available to technicians, in particular regarding
serviceability conditions for enclosure or partition walls. This will be deeply discussed
in Chapter 3.
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References
[2.1] Figure 2.3 (a): “Guest House”, Villa Grabau-Italy, photo by “PicDrops”,
20/9/2004. Figure 2.3 (c):“Oberbeuren”, Baviera-Germany, photo by “Pilot Micha”,
30/5/2010. Available at http://www.flickr.com/photos, under the license terms:
http://creativecommons.org/licenses/by-sa/2.0/. Figure 2.3 (d): “Terraced Houses”,
Crewe, England, photo by “Espresso Addict”, 4/4/2007. Available at
http://commons.wikimedia.org, under the license terms:
http://creativecommons.org/licenses/by-sa/2.0/.
[
2.2] CIB (2007) - “Enclosure Masonry Wall Systems Worldwide”, S. Pompeu Santos
(ed), Taylor&Francis/Balkema, London, UK.
[2.3] PAIVA, V. et al (1985) - “Patologia da Construção” (in Portuguese), 1º Encontro
sobre Conservação e Reabilitação de Edifícios de Habitação, Documentos Introdutórios,
LNEC, Lisboa, Portugal.
[2.4] DE VENT, I. (2011) - “Prototype of a Diagnostic Decision Support Tool for
Structural Damage in Masonry”, Supplement to the PhD thesis, Delft University of
Technology, Faculty of Architecture, Netherland.
[2.5] ABRANTES, A.; SILVA, J. (2012) - “Método Simplificado do Diagnóstico de
Anomalias em Edifícios” (in Portuguese), Livro de Obra, Gequaltec/Cadernos de Obra
(ed), Porto, Portugal.
[2.6] GASPAR, P. et al (2006) - “Técnicas de Diagnóstico e Classificação de Fissuração
em Fachadas Rebocadas” (in Portuguese), 2.º Encontro sobre Patologia e Reabilitação
de Edifícios (Patorreb2006), FEUP, Porto, Portugal.
[2.7] ARGILÉS, J. (2000) - “Arquitectura sin Fisuras” (in Spanish), Arquitectura e
Tecnologia (2), Munilla-Leria (ed), Madrid, España.
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3- Prevention of Cracking in Masonry Walls
3.1-
G
ENERAL CAUSE OF CRACKING
3
Masonry walls consisting of brick or block units (clay bricks or concrete blocks) and
their traditional finishes are able of fully meeting their performance requirements for a
long period of time. However, they often present develop cracking, humidity problems
and natural (or accelerated) degradation of materials (aging). In the last decades, various
features have been responsible for problems and distress of masonry walls and have
repercussions on their overall performance [3.1]. Amongst them, the most relevant are:
− Introduction of new materials;
− Not well evaluated enhancements of some masonry characteristics;
− Technological changes in respect of design criteria;
− Technological changes in respect to workmanship techniques and skills;
− Introduction of new building types of components;
− Compatibility issues with concrete structural elements, window sills, etc;
− Evolution of traditional rendering solutions and the compatibility of new
rendering and covering wall solutions.
Evolution of wall solutions is always linked to improvement of the wall performance as
well as faster construction but inevitably, in some cases, it will also result in new
unexpected defects. The growing expectation of end-users together with a growing
environmental awareness form new challenges for masonry wall solutions within the
construction sector (e.g. hygrothermal and acoustic code requirements).
Illustrating this, to achieve the requirements of the new thermal codes throughout
Europe, concerning the need to increase the thermal resistance concrete members in an
enclosure, designers and contractors adopted several methods, based on inconsistent and
unknown technology. Among these methods, the more relevant one promotes an
external overhang of the masonry wall of 50–80 mm, outwards from the structural
member surface (column, beam or slab), which assures an external protection of the
concrete members, thereby increasing the thermal resistance while preserving the
alignment and other aspects of the facade. This situation leads to a high concentration of
compression stresses locally which can be increased by the brick’s internal geometry. In
this case, cracking can be dramatic, even for very low levels of loading, depending on
the specific support conditions.
These poorly-supported walls can exhibit very severe cracking and, in the worst cases,
can move away from the building in the out-of-plane direction. External envelope wall
solutions using solid or perforated clay brick units are well known and they are
correctly built in many countries. However, the problem is different when the brick
resistance is very low and the percentage of horizontal voids is more than 60%,
delineated by thin clay webs of 8-9 mm thick [3.2].
The major concern is why these defects in masonry enclosure walls should occur so
regularly. Why do they recur so persistently, despite the better quality of masonry units
and the greater experience gained with this type of construction? Where is the benefit or
result of research and technological knowledge in common practice? The gap between
3
Romeu S. Vicente – Portugal
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practice and research is not effectively shaping design methods or workmanship
procedures (Figure 3.1).
Figure 3.1 - Building quality chain
Table 3.1 - Design and execution problems
Design Execution
Insufficient evaluation and knowledge
of
material properties and compatibility;
Misinterpretation of construction design
details and poor workmanship;
Insufficient detailing or access
to typical
construction details not adapted to the
construction case;
Insufficient embedment
depth of wall ties
and anchors;
Negli
gence in the estimation of potential
movement, especially for enclosure
masonry walls in the case of thermal and
moisture expansion-contraction joints;
Deficient execution of horizontal and
vertical mortar joints (influences
thermal
and acoustic properties
of the finished
wall);
Negligence in the estimation of main
structure deformations
and their effect
over masonry walls in terms of cracking
(induced stress and strain);
Incorrect execution of movement joints
and water tightness layer;
Negligence in the
case of wind loading,
special wall geometry and support
conditions (lack of specification of wall
ties, anchors, etc.);
Incorrect installation of flashings and
water barriers that compromise durability;
Misinterpretation of construction and
design codes.
Working conditions (high solar radiation,
wind, driven rain).
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The challenge is to strongly reduce or eradicate common defects in masonry walls, that
systematically occur: lack of movement joints, incorrect thermal bridge correction, lack
of wall ties, incorrect positioning of insulation in cavity walls, deficient application of
water barriers, rising damp and water tightness issues, tile and render detachment,
incorrect window sill projection, estimation of the main structure deformation, poor
seismic design including insufficient wall ties and / or stabilizing frame cramps.
Out-of-plane instability of the
external leaf due to poor support
conditions
Lack of movement joint to
accommodate thermal and
moisture movements
Seismic damage due to the lack
of connection to the backing
wall or structure (ties)
Figure 3.2 - Three major recurring defects of masonry enclosure walls
The encouragement of the use of simplified design to evaluate stresses and movements
due to various factors (wind and seismic action, thermal and moisture expansion) is
fundamental to identifying problems and expected behaviour. It is therefore important
to survey new constructions to learn more about their behaviour and special attention
should be given to very large walls. It is also very important to improve workmanship
practice [3.3].
Masonry design and verification must be promoted, particularly the use of correct
details. All the normative documents and design guidelines must give more prescriptive
solutions for validated and tested solutions.
3.2-
I
MPROVEMENT IN SERVICEABILITY BEHAVIOUR
4,5,6
3.2.1- Codes and design criteria
1,2,3
Serviceability Limit States (SLS) are related to deflection and cracking control, as well
as to any other possible structural behaviour related to comfort or functionality issues.
Changes in the appearance of non-structural masonry and finishes should also be taken
4
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Hipólito sousa – Portugal
6
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into consideration when checking SLS. The same should apply to structural masonry,
especially to unreinforced masonry, since the use of reinforced masonry tends to
decrease the occurrence of cracking problems.
There are fundamental tools for design of masonry that should be used (e.g. Eurocode 6
[3.4], North American Code [3.5], British Code [3.6]and Brazilian Standards, developed
in chapter 3.5), although they don’t analyse deeply the avoidance of cracking in SLS.
Recommendations associated with serviceability criteria are scarce, sometimes
permitting the serviceability limit state to remain unchecked. There can be few or no
specific limits for strength or deflection and references for detailing are only general, in
particular for unreinforced masonry. However, the information found in those codes
regarding SLS for structural walls may be used in non-structural walls as guidelines for
design, as well as other design codes, such as Eurocode 2 [3.7], the French code [3.8] or
the Brazilian code, which may be useful for partitions/enclosures influenced by
movements of concrete structures. Table 3.2 gives a general overview about
serviceability criteria found (x) or not found (-) for masonry in those design codes.
Table 3.2 - Overview of the SLS requirements associated to masonry
Design criteria
Codes of design
Non-structural masonry Structural Masonry
Eurocode
2
French
Code
Brazilian
Code
British
Code
USA
Code
Eurocode 6
Brazilian
standards
General
rules
Belgium
DNA
Strength/
Deflection
control
- - - X X X X X
Deformation
limits X X X X X X X
Tensile limits
- - - - - - - X
Ancillary
Reinforcement
(SLS)
- - - - - - - -
Movement
joints - - - X X X X X
Eurocode 2 [3.7] defines limits for the relative deflection of concrete structures
(span/500) in order to avoid damage in the adjacent parts, such as partition / enclosure
walls in general and applied finishes. Other limits may be considered, depending on the
sensitivity/fragility of those adjacent parts: the specific check on deflections may also be
omitted for common cases by limiting the span/depth ratios. However no specific limits
are established for structural members supporting masonry partitions or enclosure walls
in particular and there is no limit for the absolute deflections.
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The French concrete code [3.8] defines a similar philosophy; however it defines a more
demanding limit for deflections for members with a span higher than 5m
(span/1000+0,5cm) in order to avoid damage in fragile partition/enclosure walls and
applied finishes.
Eurocode 6 [3.4] states, in clause 7.1, that structures shall be designed and constructed
so as not to exceed SLS, therefore preventing cracks or deflections that might damage
partitions, finishings and technical equipment, as well as enclosures and their facings,
thus risking impairing water tightness. However, the serviceability of masonry
members should not be unacceptably impaired by the behaviour of other structural
members, such as the deformations of floors. Clause 7.2 defines general criteria for
unreinforced masonry walls and it specifies that allowance needs to be made for
differences in the properties of masonry materials so as to avoid overstressing or
damage where they are inter-connected. It also states that SLS regarding cracking and
deflection are satisfied if the Ultimate Limit States (ULS) are also satisfied, removing
the need to verify the members that comply with the span and depth ratios separately.
However, it assumes that some cracking could result when the ultimate limit state is
satisfied but no deformation limits are defined for SLS in order to avoid cracking in
structural masonry or in other non-structural elements.
Part 2 of Eurocode 6 [3.9] provides further information concerning the movement of
masonry and masonry movement joints in clauses 2.3.3 and 2.3.4, respectively. The first
clause specifies that movement joints should be used, or reinforcement should be
incorporated into masonry, in order to minimise cracking, bowing or distortion caused
by expansion, shrinkage, differential movements or creep. Clause 2.3.4 states that
positioning of movement joints must not affect the structural integrity of the building,
specifies what the design of the movement joints should take into account (type of
masonry, geometry of the structure, fire resistance, etc.) and the maximum spacing
between the movement joints for the several types of masonry in non-loadbearing walls.
The British code for the use of masonry [3.10-3.12] has a similar philosophy to EC6
[3.4, 3.9], however, it defines deflection limits for some cases. For example, it suggests
relative and absolute deflection limits (span/500 or 20mm, whichever is the lesser) for
reinforced masonry in order to avoid damage in partitions and applied finishes [3.11].
The North American Standard [3.5] follows the same EC6 [3.4, 3.9] design philosophy
as far as the SLS are concerned, and it states in the deformation requirements clause
3.1.5.2 that deflection calculations for unreinforced (plain) masonry members following
the Strength Design Method shall be based on uncracked section properties and a
general limit of span/600 is given for relative deflections. Drawings regarding
provisions for dimensional changes resulting from elastic deformation, creep, shrinkage,
temperature and moisture are also mandatory following clause 1.2.2 (h).
Regarding recent scientific research, there is some lack of guidance to support design
and detailing in SLS. Several references to avoid cracking can be found in scientific
research literature [3.13-3.21], mainly obtained from experimental studies. It is
difficult, however, to establish general references due to the difference between the
results obtained. For example, in these studies limits for relative deflections of the
supporting structure range from span/770 to span/3000 and tensile stress limits for
masonry range from 0.1 to 0.3 N/mm
2
. These deflection limits are more demanding than
the ones found in the design codes for masonry (ranges from span/500 to span/1000
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depending on the span dimension and support conditions), and no tensile strength limits
are found or considered in those design codes.
In conclusion it should be noted that, in order to reduce cracking, it is important to
better define and develop design criteria limits for serviceability behaviour of masonry
(SLS) such as deflection/strength limits, although the given references can be used as
important guidelines to design masonry in SLS. Also, in any design detailing aspects are
important, such as the movement joint detail or the use of ancillary reinforcement. This
is particularly important with unreinforced masonry or non-structural masonry since it is
almost impossible to eliminate tensile stresses in practical cases and it is important to
give more ductility to the masonry walls.
3.2.2- Detailing aspects of movements and joints
7
Owing to changes in temperature and moisture the volume of masonry units can change,
and if these movements are restrained (i.e confined), further stresses are imposed on the
structure which needs to be taken into account in the design process. Shrinkage and
accommodation of structural movements, creep, and deformation of horizontal members
and settlement of foundations also impose additional stresses.
The types of movement experienced by the different materials are shown in Table 3.3.
Eurocode 6 [3.4] states in clause 3.7.4 that the coefficients for creep, moisture and
thermal expansions shall be determined by test, either carried out or available from a
database, and proposes the deformation properties repeated in Table 3.4.
Table 3.3 - Types of movement of building materials [3.22]
Building
Material Thermal Reversible
Moisture
Irreversible
Moisture
Elastic
Deformation
Creep
Brick
Masonry X - X X X
Concrete
Masonry X X - X X
AAC
Masonry X X - X X
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Table 3.4 - Ranges of coefficients of creep, moisture expansion or shrinkage, and
thermal properties of masonry (Eurocode 6 [3.4])
a) Thermal movements
Contraction and expansion occur with temperature variation and the unrestrained
thermal movement of a given material is obtained by the product of the temperature
change, the thermal coefficient of the material and the length of the element. Eurocode 6
[3.4] proposes values for the thermal coefficient of several types of masonry, see Table
3.4, just as North American Standard [3.5] in article 1.8.3 that gives figures that also
have to be multiplied by the expected temperature change, see Table 3.5.
Table 3.5 - Thermal expansion coefficients (North American Standard [3.5])
Masonry type Thermal coefficient
Clay masonry
Concrete masonry
AAC masonry
b) Moisture related movements
The volume of most absorbent materials changes with the increase or decrease of
moisture and these changes can be reversible or irreversible, see Table 3.3. Clay
products begin to absorb moisture immediately after firing, in a complex chemical
reaction, which leads to an irreversible moisture expansion. This moisture expansion
occurs mostly in the first few weeks or months after production, see Figure 3.3.
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Figure 3.3 - Irreversible moisture expansion of fired clay units over time (Brick Industry
Association [3.22])
Eurocode 6 [3.4] stipulates a value for these changes that already takes into
consideration of long term effects, see Table 3.3, while the North American standard
only refers a single value for clay masonry brick in clause 1.8.4: k
e
=0,3mm/m.
The Masonry Society and Council for Masonry Research [3.23] states that the
irreversible expansion values range between 0.2 mm/m and 0.9 mm/m.
c) Shrinkage and creep
Shrinkage is important in concrete masonry, even though the process can take place in
other types of masonry in the mortar joints. It occurs during the cement hydration
process and, although upon wetting the units will expand to their original size, there is
an overall shortening under service conditions: if the units are wetted before
construction, they will expand and therefore the effects of shrinkage will be higher
when they dry out again. The shrinkage of concrete masonry blocks varies within rather
wide limits and the type of aggregate used and the manner in which the blocks are cured
strongly influence this process - see Table 3.6. Eurocode 6 [3.9] provides shrinkage
values for the different types of masonry - see Table 3.4, as the North American
Standard [3.5] in clause 1.8.5: k
m
=0,33mm/m.
Table 3.6 - Typical shrinkage of concrete masonry products [3.24]
Product Aggregate Curing Total Shrinkage - mm/m
Block
Dense gravel Low pressure steam 0.2-0.5
Dense gravel Autoclave 0.1-0.4
Lightweight Low pressure steam 0.4-0.8
Lightweight Autoclave 0.2-0.6
Brick Dense Low pressure steam 0.2-0.5
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Creep is a time-dependant volume change under load; it is barely of significance for
clay bricks. Loading at an early age, drying, and high water to cement ratio usually
increases the creep of masonry [3.25]. Eurocode 6 [3.4] provides a final creep
coefficient, see Table 3.4, while in clause 1.8.6 the North American standard [3.5]
provides creep coefficients dependant on the load, see Table 3.7.
Table 3.7 - Creep coefficients (North American standard [3.5])
Masonry type Creep coefficient
Clay masonry
Concrete masonry
AAC masonry
d) Movement joints
Vertical and horizontal movement joints need to be introduced in masonry in order to
accommodate the above mentioned movements and avoid the extra stresses. The
required location and thickness of those joints depend on building geometry, wall
composition, masonry material properties, and anticipated differential movements.
Clause 2.3.4 of part 2 of Eurocode 6 [3.9] defines the maximum horizontal distance
between vertical movement joints in non-loadbearing walls, see Table 3.8, but no
recommendations are made regarding loadbearing walls.
Table 3.8 - Maximum recommended horizontal distance, l
m
, between vertical
movement joints for unreinforced non-loadbearing walls (Eurocode 6 [3.9])
Type of masonry (m)
Clay masonry 12
Calcium silicate masonry 8
Aggregate concrete and manufactured stone masonry 6
Autoclaved aerated concrete masonry 6
Natural stone masonry 12
The North American Standard [3.5] does not give any details regarding movement
joints but The Masonry Society’s Masonry Designers’ Guide [3.23] separates them in
four different types: masonry control joints, which open to accommodate shrinkage of
concrete masonry and need to be placed in specific locations, see Figure 3.4; masonry
expansion joints, which close to accommodate expansion of clay or stone masonry;
construction joints, which seal the gaps between columns, windows and doors; and
building expansion joints, which isolate roofing and building framing systems.
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Figure 3.4 - Locations of movement joints [3.26]
The Masonry Society and Council for Masonry Research [3.23] states that vertical
expansions joints are not required in concrete masonry since drying shrinkage usually
exceeds thermal expansion. In clay brick masonry, however, vertical and horizontal
expansion joints need to be used as the clay masonry walls expand in both directions
due to the combination of thermal and moisture expansion. It also defines rules for the
spacing between vertical expansion joints and their size which should match the mortar
joint width (10 to 13 mm). Construction details can be seen in Figure 3.5. Drysdale and
Hamid [3.24] recommend that vertical movement joints create rectangular panels not
more than 7.6 m long in the case of masonry veneers.
Figure 3.5 - Vertical expansion joint details (The Masonry Society and Council for
Masonry Research [3.23])
Drysdale and Hamid [3.24] assume that the presence of vertical load eliminates the need
for horizontal expansion joints and The Masonry Society and Council for Masonry
Research [3.23] only relates horizontal joints to masonry and clay masonry non-
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loadbearing elements such as veneer and infills. In the former the joints are installed
below the shelf angles, see Figure 3.6, and in the later around the perimeter. The
Masonry Society and Council for Masonry Research [3.23] prescribes a width varying
from 10 to 13 mm, while Drysdale and Hamid [3.24] propose the equation:
Where is the joint thickness, is the calculated differential movement and is
the maximum cyclic deformation strain rating for the sealant.
Special attention should be given to construction joints between masonry walls attached
to structural frames. If the walls are not intended to provide lateral stiffness, joints need
to be provided, see Figure 3.7.
Figure 3.6- Example of support system showing provision for movement [3.27]
The importance of choosing the correct material for the sealant in all types of joints is
also highlighted in The Masonry Society and Council for Masonry Research [3.23] and
Drysdale and Hamid [3.23], both referring to water-tightness, durability, good
compression properties (expansion joints) and elongation properties (control joints) as
key aspects. Klingner [3.28] states that exterior sealants should be replaced every 7
years since ultraviolet light and ozone deteriorate the sealant’s properties.
Wall tie
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The wrong place for a control joint because
cracks may seek a path of less restraint
Control joints located at window opening to avoid
random cracking
Control joints at columns and pilasters
Figure 3.7 - Control joints [3.29]
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3.2.3- Permissible deviations and tolerances
8
Clause 9.1 of Part 1-1 of Eurocode 6 [3.4] states that all work shall be constructed in
accordance with specified details within permissible deviations and by skilled and
experienced personnel. It also states that, if the requirements of part 2 of Eurocode 6
[3.9] are followed, the above mentioned specifications are satisfied, and clause 3.2 of
the latter specifies that deviations of the constructed masonry should not exceed the
values specified in the design, and if they are not specified then the values should be the
lesser of: values on table 3.1 of Eurocode 6 [3.9] - see Table 3.9 and Figure 3.8 and
values from locally accepted practice.
Table 3.9 - Permissible deviations for masonry elements
The North American standard [3.30] defines a tolerance of ±3 mm for the mortar bed
joints of clay, concrete and stone masonry, which should have a thickness of 9.5 mm,
while head joints are permitted to vary by -6.4 mm to +9.5 mm. This same standard
refers that tolerances for alignment (on plan or elevation), for level (on elevation) and
for plumb (verticality) should be annotated in the contract documents together with
tolerances for the vertical expansion joints, which should be such that the minimum
sealant joint width is not greater than the specified width minus the negative tolerance.
8
Paulo B. Lourenço – Portugal
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Verticality (1-storey height; 2-building height)
Vertical alignment (1-intermediate floor)
Figure 3.8 - Maximum vertical deviations (Eurocode 6 [3.9])
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3.3-
C
RACKING PREVENTION IN MASONRY PARTITION WALLS
9
3.3.1- General
Interior walls have as their function the separation between different spaces (rooms).
They don’t have a structural role, so their thickness is generally only 5 to 10 cm. They
are often constructed in brittle masonry materials such as clay bricks or blocks, concrete
blocks (dense or lightweight), calcium silicate units, gypsum, etc.
This means that their ability to adapt to deformations in the building is very low - they
are building elements that can be exposed to cracking in various forms.
The cracks have an influence on the aesthetic function and on some of their physical
properties such as noise insulation.
In practice, the cracks in the interior walls can often cause litigation since repair costs
can be very high if properly done.
3.3.2- Origin of defects in interior walls (partitions)
Excessive deformation of slabs or beams supporting partitions is the most frequent
cause of damage to partitions. While the beam or slab can deflect without any damage,
the supporting brittle masonry elements cannot follow and will crack (Figure 3.9).
Figure 3.9 - Cracks in a partition due to the deformation of support
The form of these cracks depends on several factors:
− The ratio of length to the height of the wall;
9
Oscar Pfeffermann – Belgium
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− The type and quality of the masonry material in the partition;
− The presence of door and window openings in the partition;
− Any interaction with other walls, partitions, columns, etc.
Different situations may occur.
a) The deflection of the slab on the upper level of the partition is higher than that at
the foot of the partition (Figure 3.10).
Figure 3.10 - Cracks in a partition due to the deflection of the upper support
In this case the partition takes on a structural function. It will behave as a deep beam
under flexure but the partition was not designed for this function so if the tensile
stresses in the partition produced by such a deflection are higher that the tensile strength
of the masonry, cracks will occur (Figure 3.11).
Fig 3.11 - Partition is acting as a deep beam in flexure
These are similar to the cracks in a concrete beam under flexure. In reality a new
distribution of the loads occurs with the partition as a structural element. The part of the
load distributed to the partition depends on:
− The stiffness of the partition;
− The rigidity of the partition support;
− The position of the partition in relation to the other supports (walls, beams, etc.);
− The physical characteristics of the masonry of the partition.
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An example: a partition supported by a rigid slab situated half way between two
structural walls, will take 15 to 30% of the total load.
If the support of the partition is not stiff, the transmitted load will be only 2 to 11% of
the total load.
Physical elements such as shrinkage and expansion may influence 60 to 70% of the
movement if the support is not stiff. In case of a stiff support this value is only 10 to
15%.
b) The deflection of the slab at the foot of the partition is excessive
This is the most common masonry defect for partitions. A relatively stiff masonry
partition built on a slab or a beam cannot follow the deformation of its support without
cracking. The structural elements of reinforced concrete or steel may deflect without
disturbing the stability of those elements but this is not compatible with good
serviceability of the masonry partition. Cracks are situated at the foot of the partition
(Figure 3.12) or can often occur between the slab and partition (Figure 3.13).
Figure 3.12 - Crack pattern by slab deflection
Figure 3.13 - Crack between slab (beam) and partition
Tests conducted at the Belgian Building Research Centre (CSTC) [3.31, 3.32, 3.33]
showed that the cracks occur:
− By lack of shear strength within the mortar (Figure 3.14);
− By lack of bond between the mortar and support or the mortar and masonry unit
(Figure 3.15).
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Figure 3.14 - Crack in the mortar
Figure 3.15 - Crack between blocks and mortar (bond between block and mortar)
The tests also demonstrated other interesting points:
− After cracking, an arch (Figure 3.13) will form in the wall and the partition will
act as a “deep beam”;
− The cracking pattern will depend on the dimensions, the type of masonry units
used and the presence of any openings;
− A partition with a small l/h will behave as a “deep beam” and the crack will occur
between the slab and the partition (Figure 3.16);
− In the case of a door opening, the crack patterns will depend on the position of the
opening (Figure 3.17);
− In case of a central opening with masonry above the lintel, the cracks will have
the same form as for a plain wall with a discontinuity at the opening;
− In the case of a lateral opening, the first cracks occur at the opening dividing the
partition in two: one with the opening and one without the opening, this last one
being similar to the behaviour of a plain wall with the characteristic cracks at the
bottom (Figure 3.18).
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Figure 3.16 - Partition is acting as a beam crack pattern
Figure 3.17 - Different patterns of cracks (without opening; with opening in different
positions)
Figure 3.18 - Lateral opening
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3.3.3- Prevention of cracks
There are 2 ways:
− Limitation of the deflection of the supports (slabs, beams);
− Increasing the deformability of the partitions.
The two ways may be used together.
a) Limitation of the deflection of the support
In the past a lot of studies and experimental tests were conducted to determine the
maximum allowable deflection [3.31, 3.32]. The deflection is a movement of an element
under flexure between two states - A1-A2 [3.34] (Figure 3.19) or two time periods (T1
– T2). There is:
− the initial state or initial time period or the reference state (A1, T1);
− the measurement state or time period (A2, T2).
Figure 3.19 - Deflection of the support
The loads producing deflection may also be different:
− Self-weight (G);
− Self-weight and other permanent loads (G+P).
There can also be different design conditions:
− Self-weight, permanent loads and variable loads (G+P+Q).
A distinction is made between:
− The elastic deformation;
− The long term deformation due to creep in case of concrete.
The situation is complicated because of the different components of the load
(permanent, transient) and the long term deformation (which is increasing with time).
Let’s see which deformation (deflection) must be taken into account for partitions
(Figure 3.20)
(A1, T1)
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Figure 3.20- Components of the deformation of a support
i. Deflection (fa) of concrete slabs Deflection (fb) affecting the behaviour of the
partition.
In this case the following must be taken into account:
− An initial deformation due to construction (it can also be a camber introduced into
the formwork);
− A deflection under self-weight (may be a direct deflection and a deformation in
time (creep);
− A direct deformation (elastic deformation) and a long term deformation (due to
creep) due to the building construction elements such as non-structural elements;
− A deformation due to the mobile loads from the utilization of the floors.
ii. Deflection (fb) affecting the behaviour of the partition.
− Long term deflection under the already present permanent loads (self-weight,
other building elements);
− Long term deflection under the new permanent loads (self-weight of the wall,
other building elements);
− Elastic deflection under the permanent loads placed after the erection of the
partitions;
− Elastic deflection under the transient loads.
This deflection “fb” is at the heart of the problems associated with partitions. In
conclusion this deflection must be limited. This is not so easy. There is a complexity
due to the stages of load application, to the nature and erection of the partition and last
but not least the calculation of the deflection. We will see this in the next section.
iii. Total deflection “fmax” is the deflection under the total value of all the loads
(permanent, mobile) the elastic and the long term deformation.
iv. The deflection “fc” is a deformation under the mobile loads (static and dynamic
action).
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3.3.4- Calculation of the deflection
The deflection of a reinforced concrete slab or beam is made according Eurocode 2.
This document gives the information concerning the elastic and long term deformation
(due to creep). The calculation must take into account:
− The geometry of the compartments (rooms);
− The erection stages of the different construction components.
In the calculation of the deflection, a method that is often used is to consider a part of
the service loads as permanent loads. In Belgium, the advice is to take as permanent
load:
− ¼ of the service loads, if they are not higher than 5 kN/m²
− ½ of the service loads if they are higher than 5 kN/m²
− ¾ of the service loads for rooms used as book storage, archives, etc.
3.3.5- Limitation of the deflection
As already mentioned, it is not easy to determine limit values for the deflection. A lot of
factors influence the amount of deformation which partitions can sustain. A recurring
theme is the lack of research concerning this subject. This may be partially due to the
fact that the problem can’t be solved with theoretical considerations. Different practical
observations on buildings with cracks on the partitions and different laboratory tests on
the deformability of the partitions [3.33, 3.34, 3.35] were made in the frame of the
Belgian Building Research Station (CSTC). The tests were conducted in the Laboratory
of Civil Construction of the University of Brussels.
The conclusion was that, parallel with some “guidance” values for the deflection, it
must also be considered how to increase the deformability capacity of the partition.
It is impossible and not economic to provide supports stiff enough to exclude cracks
occurring. It is also important to improve the construction details. Some advice will be
given later concerning this technical aspect.
The “empirical” values that were proposed [3.34] and were also taken over by different
countries can be summarized as follow:
− Walls without openings on their surface fb ≤ L/500
− Walls with openings fb ≤ L/1000
− Walls with openings but with special technological means, to avoid cracks fb ≤
L/500
Where L is the span and fb the deflection produced after the erection of the partition.
3.3.6- Practical means to protect partitions from cracking
a) Make the partition independent of the structure
This is the most efficient method (Figure 3.21) and is taken from the Belgian Standard
NBN EN 1996 [3.36].
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Figure 3.21 - Partition separated from its support and reinforced in the joints
The partition is separated from the bearing slab or beam with a damp proof membrane
(dpc/dpm) or some other layer and with reinforcement placed in the mortar joints of the
wall. Also the top of the wall must be separated to allow the deflection of the upper slab
to take place without any significant loading on the wall, and the lateral stability should
be ensured. The partition then behaves like a separate, reinforced wall beam and no
longer follows the movement of the floor or the beam.
The eventual opening between floor and partition is covered by a decorative strip at the
bottom.
b) Opening in the wall
Provide joint reinforcement above the opening (Figure 3.22). Try to make a joint close
to the opening (Figure 3.23). In this case the two walls will deform separately, thus
avoiding corner cracks.
Figure 3.22- Reinforcement above the opening
h
B
A
L
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Figure 3.23 - Joint close to the opening – opening reinforced in the joints
c) Erection of the walls
Try to do it as late as possible after the construction of the structure so that part of the
deflection has already occurred. When walls are built above each other on different
levels, Figure 3.24 shows two possible ways to progress the masonry construction.
Masonry to be built after the conclusion of the concrete structure
Figure 3.24 – Examples of two alternative ways of constructing masonry partitions
walls in different levels of concrete framed buildings [adapted from 3.25]
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3.4-
C
LADDING CRACKING IN
UK
AND
I
RELAND
10
The combined moisture and thermal expansion of clay masonry units is one of the main
reasons for potential cracking distress to masonry cladding to framed buildings. In the
UK and Ireland, the use of concrete masonry or calcium silicate units in external
cladding is generally less than that for clay and combines moisture shrinkage with
thermal movement. In the UK and Ireland either steel or reinforced concrete frames are
commonly used depending on the cost at the time of building and the site constraints
present. The use of timber frame construction is also popular for residential - type
construction of up to 5-7 floors.
Distress in cladding has been witnessed and remedies developed since the late
1950s/early1960s when a discernible trend of multi-storey construction was seen. The
commonest form of distress seen on cladding to framed buildings is the vertical or
inclined crack – indicative of tension failure when the cladding is wishing to contract
but restrained from doing so. Furthermore, the movement becomes apparently greater
with walls of small height - such as parapets. In almost any city or urban scene
throughout Europe, the trained eye can find some degree of cracking distress with
masonry parapets, Figure 3.25.
Figure 3.25 - Movement failure of parapets in SE Europe
In a similar way, distress can be seen on the odd building in any city in both Europe and
North America, Figure 3.26 and 3.27.
On standard storey height walls, this can take the similar form of a vertical/near-vertical
or an inclined crack. This is common when the distance between vertically aligned
movement joints is large. Another form of distress seen is where horizontally aligned
movement joints appear to have closed causing either visible cracking distress or,
indeed, signs of a visible repair. In the UK and Ireland, this form of distress is not
uncommon.
10
John Morton – UK
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Figure 3.26 - Movement failure of façade to framed building in USA.
Figure 3.27 - Movement failure of parapets in a more modern building in USA
Figure 3.28- Micro cracking -in render on blockwork sub-panels within a clay brick
enclosure wall. This cracking will only be detectable by professionals and, in terms of
movement design, such an outcome can be considered a success
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Figure 3.29 - Insufficient provision for movement has been made resulting in the joint
closing allowing a build-up of stress in the brickwork façade. This will have been
caused either by a poor design detail or poor workmanship
The route to avoid distress and to achieve successful cladding on framed buildings can
be summarised as follows:
1) Acknowledge that there will be movement in the external masonry cladding and then
form a plan to accommodate this movement successfully;
2) One way to achieve this is to place regular joints in the masonry by introducing
horizontal and vertical joints at appropriate centres. In the design guidance available
in any country/region, there is normally a recommended maximum horizontal
distance between vertical joints so that the maximum length of any panel is restricted
(such lengths can usually be exceeded somewhat when bed-joint reinforcement is
used);
3) Depending on the type of frame and the detail of the panel support, horizontal joints
may be required at regular intervals;
4) It is important that, in both the vertical and horizontal joints, the width of the joint is
appropriate to the panel height/length – i.e. the joints don’t ‘close’ because they are
too narrow or otherwise become ineffective;
5) It is important too that the joint detail allows movement to take place – i.e. highly
compressible fillers are specified and installed;
6) The designer may find it surprising when considering design aspects, that over the
years, the writer has found that workmanship can be responsible for the joints
becoming ineffective. Inclusion of mortar in horizontal joints can be quite common
when forensic examination of masonry is done to establish the reason for cracking
prior to repair; similarly, it is not uncommon to find that incompressible filler
material has been used in the joints: this can be seen more than might be imagined or
expected – often where correct joint details are given in the drawings;
7) A current trend which has some potential to cause future problems is the use of shelf
angles at every 2nd or 3rd floor. In itself this should be perfectly feasible with
adequately sized horizontal joint widths; some experience gleaned demonstrates that
some cladding when constructed has unrealistically small joint widths when shelf
angles are positioned at 10 - 12m vertical height – particularly with shrinking frames;
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8) Additional simple ‘rules’ exist which are born more out of experience than theory;
They are ‘almost’ universal although depending on the region, the odd parameter
may vary – such as the maximum length of masonry between vertically aligned
movement joints; These rules include:
− introduce a vertical joint at positions where the wall height changes significantly;
− introduce a vertical joint at positions where the wall thickness changes
significantly;
− take appropriate care when mixing two different materials such as (expansive)
fired clay units with (shrinking) concrete or calcium silicate units in solid walls;
− in a solid wall, take appropriate care when mixing two different types of the same
material – such as (expansive) fired clay units – both of which may have different
moisture movement characteristics;
− take appropriate care when mixing two different materials such as (expansive)
fired clay units with (shrinking) concrete or calcium silicate units in cavity
walling; It is possible when using solid metal ties to find the wall develops a
‘bend’ when an inner concrete block leaf is joined to an outer clay unit leaf using
ties which cannot flex or accommodate moment in the vertical direction;
− with units which have a propensity to shrink be careful with the sub panels which
are formed under windows that their length does not become excessive compared
to their height;
− take appropriate care when the introduction of a movement joint might introduce
structural weakness – such as at the junction between a panel and a pier in a free
standing wall;
− any ‘fixings’ placed across a movement joint must be capable of accepting the
expected movement within the joint width;
9) Long term performance of the masonry can reasonably be expected when simple
procedures such as those above are followed – modified as necessary to suit the
location of the building.
Other major approaches to designing cladding on tall buildings exist which are quite
different from some of the suggestions given above. One approach – off-the-frame-
cladding – has been used selectively for decades and successful buildings have been
constructed in Switzerland and USA. Some 30 years or so ago a few buildings were
constructed in UK. This form of design approach has not caught on in the imagination
of designers despite the additional freedom that it offers: it is, however, an alternative
method. A greatly undervalued benefit is the almost zero propensity to workmanship
‘error’ due to the basic simplicity of the approach.
Finally, an aspect worth mentioning is the topic of education. Where, one wonders,
does a young designer learn of the concept of ‘making masonry work’ in buildings. In
engineering schools in the UK and Ireland, engineers may be taught the calculation
methods to satisfy design codes. Having said this, most schools spend a majority of the
time teaching Steel and Concrete structural design; there is usually far less content on
structural Masonry and Timber design. In terms of being introduced to designing and
detailing masonry cladding, one suspects that it is down to be learnt during the first job
to be tackled in anger in practice; it is usually learnt from colleagues in the same office.
The quality of learning is therefore really down to the quality of existing knowledge
within the practice which suggests in part a hit-or-miss approach. In a particular office
or region, for example, if the design approach with masonry is not well understood, the
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poor level of design knowledge becomes self-fulfilling in the next generation of
designers. In some areas/countries, there is a role for the educational community to pick
this up – were this possible. In other areas/countries it is reasonable to expect that it is
being adequately or well provided by the various schools.
3.5-
B
RAZILIAN
S
TANDARDS FOR
P
REVENTION OF
C
RACKING IN
M
ASONRY
11,12,13
3.5.1- Introduction
Good structural performance is related to the prevention of reaching both Ultimate
(ULS) and Service Limit States (SLS). The SLS are usually related to preventing the
following:
a) damage that jeopardizes construction aesthetics, durability, sound and heat
insulation or produces water ingress;
b) excessive displacements that affect the structural behaviour or the aesthetics;
c) excessive or uncomfortable vibrations.
Usually, national or regional Standards establish criteria that should be followed in
order to avoid, or at least minimize, the aforementioned situations. Those criteria are in
place to ensure that a minimum standard of working methods for the constructions is
achieved. Regarding masonry buildings, detachment and cracking are the most likely
causes of failure, which are directly related to SLS and briefly described in (a) and (b)
below. Independent of their classification [3.38] regarding type of element and material,
position and cracking pattern, cracks should not be discernible and jeopardize the
building performance, despite the fact that in many cases it is inevitable, due to the
intrinsic brittle behaviour of masonry. As cracking is associated with masonry
deformation, the current standards normally establish parameters relating to:
a) mortar deformability;
b) limit of dimensions and number of chases in structural elements;
c) movement joints;
d) deformation limits of both masonry walls and bearing components.
The following sections show some requirements found in the Brazilian Standards for
structural masonry: ABNT NBR 15961-1 [3.39] and ABNT 15812-1 [3.40] for concrete
block and clay block masonry, respectively.
3.5.2- Masonry deformability
Due to lack of experimental data, the following safe parameters can be adopted (Table
3.10):
11
Márcio Corrêa - Brazil
12
Ercio Thomaz - Brazil
13
Humberto Roman – Brazil
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Table3.10 - Properties of masonry deformation
Property Value
Concrete Clay
Modulus of elasticity 800 f
pk
≤ 16 GPa (*1)
600 f
pk
≤ 12 GPa
Poisson coefficient 0,20 0,15
Coefficient of thermal expansion 9,0 x 10
-
6
o
C
-
1
6,0 x 10
-
6
o
C
-
1
Coefficient of moisture expansion - 300 x 10
-
6
mm/mm
Shrinkage coefficient 500 x 10
-
6
mm/mm (*2) -
(*1) f
pk
is the 2 blocks prism characteristic compressive strength
(*2) shall be increased to 600 x 10
-3
mm/mm when blocks are produced with natural curing
To verify the Serviceability limit state the following is recommended:
reduce by 40 % the deformation modulus in order to approximately consider the
masonry cracking effect;
double the estimated elastic deformation associated to loading to obtain the
approximated creep (dead load).
3.5.3- Limits for dimensions and cuts in masonry
a) Effective thickness
The standard code does not allow effective thickness smaller than 140 mm for two or
more story buildings, and never less than 115 mm.
b) Slenderness ratio
The slenderness ratio, (height / effective thickness) must follow the limits described in
Table 3.11.
Table 3.11 - Maximum values of slenderness ratio for structural walls and columns
Unreinforced elements 24
Reinforced elements 30
Note: For masonry partition walls the maximum slenderness ratio is 30.
c) Wall chases and recesses
Horizontal individual chases longer than 400 mm or more than one chase in a same wall
adding up to more than 1/6 of the wall’s total horizontal length are not allowed in walls
with a structural function; vertical chases higher than 600 mm in walls define a joint
between two distinct walls; water pipes shall not pass inside structural walls, except
when the installation and maintenance do not require chases.
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3.5.4- Control and movement joints
a) Movement joints
Movement joints should be placed at least every 24 m in a façade’s length. This limit
may change if a more precise evaluation of the thermal and shrinkage effects over the
structure is carried out. The presence of bond beams or reinforcement in the bed joints
and a more precise evaluation of the temperature and shrinkage variation effects can
allow changes on this limit.
b) Control joints
The need for vertical control joints should be evaluated to avoid cracks due to
temperature changes, shrinkage, sudden changes in loading and thickness or wall height
changes; for single plane masonry walls, vertical control joints not exceeding the limits
of Tables 3.12 and 3.13, for concrete and clay blocks respectively, shall be provided if
and when there is no accurate assessment of the specific conditions.
Table 3.12 - Maximum distance between vertical control joints – concrete block
masonry
Wall
Position
Limit (m)
Unreinforced
masonry
Masonry with reinforcement rate higher or equal to
0.04% height versus thickness
External 7 9
Internal 12 15
NOTE 1 The above limits shall be reduced by 15% if there is an opening in the wall
NOTE 2 If the blocks are cured in the
natural environment the limits shall be reduced by 20% if there is
no opening in the wall
NOTE 3 If the blocks are cured in the natural environment the limits shall b
e reduced by 30% if there is
an opening in the wall
Table 3.13 - Maximum distance between vertical control joints – clay block masonry
Wall Position Limit (m)
Wall thickness ≥ 140mm Wall thickness = 115mm
External 10 8
Internal 12 10
NOTE 1 The minimum control joint thickness shall be of 0.13 % of the distance between joints
NOTE 2 The above limits shall be reduced by 15% is there is an opening in the wall
NOTE 3 The above limits may be changed if technically justified horizontal reinforcements
are placed
into the bed joints
3.5.5- Deflection limits
The final deflections of any element, including effects of cracking, temperature,
shrinkage and creep are related to its span L. They shall not be higher than L/150 or 20
mm for cantilever and L/300 or 10 mm for all the other cases (Note 1: Those values
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should be revised in a future issue of the Brazilian Standards, since the consensus
reached is that they are too large). These displacements may be partially compensated
by in-built deformations not higher than L/400 (Note2: The efficiency of in-built
deformations is questionable).
Structural elements such as beams, slabs, etc., bearing masonry walls shall not have
displacements greater than L/500, 10 mm or θ = 0.0017 rad after being loaded by the
walls.
3.5.6- Observations regarding reinforced concrete structures
Reinforced concrete structures are currently being used in approximately 68 % of
Brazilian residential buildings [3.41]. The standard code for structural concrete design,
ABNT NBR 6118 [3.42], establishes displacement limits according to their effects, as
shown in Table 3.14.
Table 3.14- Deflection limits – ABNT NBR 6118 [3.42]
Type of effect Example Displacement to
consider Limit
Effects on non-
loadbearing
elements
Masonry, window
frames and rendering
After wall Construction
L/500
(*1)
, 10 mm or
θ = 0,0017 rad
(*2)
Light panels and
Telescopic window
frames
After panel installation
L/250
(*1)
or
25 mm
Lateral building
movement
Due to frequent
combination of wind
actions (Ψ
1
=0,30)
H/1700 or
Hi/850
(*3)
between
floors
(*4)
Thermal vertical
movements
Due to temperature
differences
L/400
(*5)
or
15 mm
(*1) – Span L measured in the plane of the wall; (*2) – Rotation of bearing load elements; (*3) – H is the
total building height and H
i
is the level difference between two closed pavements; (*4) – This limit
applies to lateral displacement between two neighbouring floors due to horizontal forces. The
displacements due to axial deformation of columns shall not be included; (*5) – The value L refers to the
distance between the external column and the first internal column.
3.5.7- IPT Recommendations
IPT (Technological Research Institute of São Paulo/ Brazil) proposed a document to be
discussed within the building sector. This document recommends displacement limits
for structural elements and foundations that support clay block partition walls,
highlighting that cracking and creep effects should be taken into account. They are
summarized in Table 3.15.
Special building details should be provided to separate or reinforce the interfaces
between the structural element and the partition wall, when the recommended limits are
exceeded.
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Table 3.15 - Displacement limits - IPT [3.43]
Cause Displacement to consider Limit
Foundation settlements Total L/400
(*1)
Deflection of slabs and
beams
Total
After wall construction
L/400
(*2)
L/600
Beam and slab torsion Rotation of the support
element on the wall plane θ = 0,0017 rad
(*1) – L is the distance between foundation elements or the wall length when the foundation is
continuous; (*2) – L is the structural element span
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References
[3.1] SILVA, J. (2002) - “Alvenarias Não Estruturais. Patologias e Estratégias de
Reabilitação” (in Portuguese), Seminário - Paredes de Alvenaria: Situação Actual e
Novas Tecnologias, FEUP, Porto, pp.187- 206.
[3.2] VICENTE, R.; SILVA, J (2007) - “Defects of Non-Loadbearing Masonry Walls
Due to Partial Basal Supports”, Journal of Construction and Building Materials, 21, pp.
1977-1990.
[3.3] Vicente, R.; Rodrigues, H.; Varum, H.; Costa, A.; Silva, J (2012) – “Performance
of Masonry Enclosure Walls: Lessons Learnt from Recent Earthquakes”, Earthquake
Engineering and Engineering Vibration, 10 (4).
[3.4] CEN (2005) - “Eurocode 6 - Design of Masonry Structures - Part 1-1: General
Rules for Reinforced and Unreinforced Masonry Structures (EN 1996-1-1)”, CEN,
Brussels, Belgium.
[3.5] MSJC (2005) - “Building Code Requirements and Specification for Masonry
Structures” (ACI 530/ASCE 5/TMS 402 and ACI 530.1/ASCE 6/TMS 602), USA.
[3.6] BSI (2005) - "Code of Practice for the Use of Masonry” (BS 5628- Part1, 2 and 3),
BSI, London, UK.
[3.7] CEN (2004) - “Eurocode 2: Design of Concrete Structures. Part 1-1: General
Rules and Rules for Buildings (EN 1992-1-1), CEN, Brussels, Belgium.
[3.8] BAEL (2000) - “Règles Techniques de Conception et de Calcul des Ouvrages et
Constructions en Béton Armé Suivant la Méthode des États Limites“ (DTU P 18-702)
(in French), Règles BAEL 91 Révisées 99, Fascicule 62, titre 1
er
du CCTG - Travaux
Section 1 : Béton Armé, CSTB (CD-Reef V3 - Edition 156), France.
[3.9] CEN (2006) - “Eurocode 6: Design of Masonry Structures - Part 2: Design
Consideration, Selection of Materials and Execution of Masonry (EN 1996-2)”, CEN,
Brussels, Belgium.
[3.10] BSI (2005) - “Code of Practice for the Use of Masonry – Part1: Structural Use of
Unreinforced Masonry (BS 5628-1)”, BSI, London, UK.
[3.11] BSI (2005) - “Code of Practice for the Use of Masonry – Part2: Structural Use of
Reinforced and Prestressed Masonry (BS 5628-3)”, BSI, London, UK.
[3.12] BSI (2005) - "Code of Practice for the Use of Masonry – Part3: Materials and
Components, Design and Workmanship (BS 5628-2)”, BSI, London, UK.
[3.13] PFEFFERMANN, O. (1969) - "Fissuration des Cloisons en Maçonnerie Due une
Déformation Excessive du Support - Part 1 (in French)", CSTC, Revue, Bruxelles.
[3.14] PFEFFERMANN, O.; PATIGNY, J. (1975). "Fissuration des Cloisons en
Maçonnerie Due a une Déformation Excessive du Support - Parte 2 (in French)", CSTC,
Revue, Bruxelles.
[3.15] DIAS, J. (1994) - “Fissuração de Paredes de Alvenaria Devido ao Movimento
dos Elementos de Suporte (in Portuguese)”, 2.º Encontro sobre Conservação e
Reabilitação de Edifícios, Lisboa, Portugal, p.785.
Defects in Masonry Walls.
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[3.16] PFEFFERMANN, O. (1968)- “Les Fissures dans les Constructions: Conséquence
de Phénomènes Physiques Naturels (in French)“, Annales de L'Institut Technique du
Bâtiment et des Travaux Publics, Bruxelles.
[3.17] PEREIRA, M. (2005)- “Anomalias em Paredes de Alvenaria sem Função
Estrutural (in Portuguese)”, Msc Dissertation, University of Minho. Portugal.
[3.18] PAGE, A. (2001)- “The Serviceability Design of Low-Rise Masonry Structures”.
Prog. Struct. Eng Mater., 3, pp.257-267.
[3.19] HOLANDA, G.; RAMALHO, M.; CORRÊA, M. (2007)- “Experimental and
Numerical Analysis of Masonry Walls with Openings Subjected to Differential
Foundation Settlements”, 10th North American Masonry Conference, St.Louis,
Missouri, pp.26-27.
[3.20] BERANEK, W. (1987)- “The Prediction of Damage to Masonry Buildings
Caused by Subsoil Settlements”, Heron, 32(4), pp.55-93.
[3.21] MEYERHOF, G. (1953)- “Some Recent Foundation Research and its
Application to Design”, The Structural Engineer, 31, pp.151-167.
[3.22] BRICK INDUSTRY ASSOCIATION (1991) - “Movement Volume Changes and
Effect of Movement”, Technical Notes 18 Revised, Reston, Virginia.
[3.23] THE MASONRY SOCIETY AND COUNCIL FOR MASONRY RESEARCH
(2005)- “Masonry Designers' Guide”, Boulder, Colorado.
[3.24] DRYSDALE, R., AND HAMID, A. (2008)- “Masonry Structures Behaviour and
Design”, Boulder, Colorado.
[3.25] SAHLIN, S. (1971)- ” Structural Masonry”, Prentice-Hall, Inc.
[3.26] BEALL, C. (1987)- “Masonry Design and Detailing”, McGraw-Hill, New York.
[3.27] BSI (2005) – “Code of Practice for the Use of Masonry – Part 3: Materials and
Components, Design and Workmanship (BS 5628-3)”, BSI, London, UK.
[3.28] KLINGNER, R. (2009)- “Masonry Structural Design”, McGraw Hill.
[3.29] PANARESE, W.; KOSMATKA, S.; JR., F (1991) - “Concrete Masonry
Handbook”, Portland Cement Association, Skokie, Illinois.
[3.30] MSJC (2008)- “Specification for Masonry Structures (ACI 530.1/ASCE 6/TMS
602)”, USA.
[3.31] PFEFFERMANN, O. (1975) - “Fissuration des Cloisons en Maçonnerie Due à
une Déformation Excessive du Support - Part 1” (in French), CSTC, Revue, Bruxelles.
[3.32] PFEFFERMANN, O.; PATIGNY, J. (1975) - “Fissuration des Cloisons en
Maçonnerie Due à une Déformation Excessive du Support – Parte 2” (in French),
CSTC, Revue, Bruxelles.
[3.33] PFEFFERMANN, O. (1968) – “Les Fissures dans les Constructions:
Conséquence de Phénomènes Physiques Naturels“(in French), Annales de l’institut
Technique du Bâtiment et des Travaux Publics, Paris.
[3.34] PFEFFERMANN, O. (1980) – “Déformations Admissibles dans les
Bâtiments“(in French), CSTC – N.I.T. 132, Bruxelles, Belgium.
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[3.35] O. PFEFFERMANN (1967) – “Fissuration des Maçonneries” (in French), CSTC,
NIT65, Bruxelles, Belgium.
[3.36] CEN (2012) - “Eurocode 6: Design of Masonry Structures - Part 2: Selection of
Materials and Execution of Masonry (Belgian Standard NBN EN 1996-2)”, Bruxelles,
Belgium.
[3.37] SILVA, R. et al. (2009) – “Manual da Alvenaria de Tijolo - 2ª edição” (in
portuguese), APICER/CTCV (eds), pp. 163-208.
[3.38] GRIMM, C. (1997) – “Masonry Cracks: Cause, Prevention and Repair”,
Masonry International, 10 (3).
[3.39] ABNT (2011) - “NBR 15961-1 (Ed. 1): Structural Masonry - Concrete Blocks.
Part 1: Design”, Rio de Janeiro, Brazil.
[3.40] ABNT (2010) - “NBR 15812-1 (Ed. 1): Structural Masonry - Clay Blocks. Part 1:
Design”, Rio de Janeiro, Brazil.
[3.41] CONSTRUCTION COMMUNITY (2008) - “Technological Level Poll. São
Paulo,2008”,http://www.abcp.org.br/downloads/arquivos_pdf/Comunidade_da_Constru
cao_Pesquisa_Nivel_Tecnologico_2008.pdf (Accessed on: 30/01/2012).
[3.42] ABNT (2003) - “NBR 6118 (Ed. 1). Design of Structural Concrete - Procedure”,
Rio de Janeiro, Brazil.
[3.43] IPT (2008) - “Clay Block Partition Walls - Good Practice Code”, Technological
Research Institute of São Paulo, Brazil.
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4- Repair Strategies for Cracking in Masonry Walls
4.1-
P
ROBLEM ASSESSMENT AND STRATEGIES
14
The cracking of masonry walls results when quality standards or serviceability
requirements are unsatisfactorily complied with. The selection of repair strategies is
conditioned by the type of defect, its causes and the features that are intended to be
improved (stability, structural and fire safety, thermal and acoustic comfort, energy
efficiency, water-tightness, or others).
There are two main strategies to repair masonry walls; they can be used alternatively or
combined:
− repair, locally, any single defect with a specific technique (example - local crack
sealing or tying, controlled demolition and reconstruction, reinforcement of corner
angles - high stress areas, etc.);
− global improvement of masonry performance, with an extended and multi-purpose
repairing technique (example - global tying and bed joint reinforcement, general
grouting or reinforced coating layer, external insulation, etc.).
Figure 4.1 - Flowchart for typical procedures of cracking repair
Choosing one or both of these strategies depends on several factors:
− the number and spatial distribution of the defects in the wall;
− the diversity of defects observed;
− the existence of a multi-purpose repairing technique, for the multiplicity of
defects, compatible with the construction of the masonry, its coating and finishing
solution.
The most frequent groups of defects are cracking, water penetration, ageing and local
degradation. The structural stability is only affected in a few cases of cracking but,
when it happens, it is the most important factor concerning the repairing strategy and
the repairing techniques [4.1].
For all the defects not having structural consequences, there are several approaches that
can be taken together to obtain a more durable versus economic solution: suppression of
the defect, replacement of the affected materials, concealing or hiding of the defects,
14
José M. Silva – Portugal
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protection against aggressive agents, elimination of causes and upgrading of specific
features.
Soft techniques, such as repairing coatings and finishing - like thin reinforced mortar
layers (eventually, over external insulation boards / ETICS), elastic and water-tight
paints coats – are used when the main defects affect all of the wall but only its external
surface (cracking, humidity, ageing, etc.). They are often used as supplementary
corrective action after the local repairing of cracks using wall ties, embedded steel bars,
anchors, etc.
Considering structural walls, the selected repairing techniques must re-establish the
continuity that allows the correct (and, if possible, the original) transmission of
compressive, tensile, shear and flexural forces, without exceeding masonry strength and
avoiding local stress concentration under the expected loads and imposed deformation,
although an upgrading of strength cannot be neglected if the actions responsible for the
previous failure are not reduced and will remain effective [4.2]. In these situations, the
repairing strategy should involve other construction components related to the masonry
walls, such of slabs, beams and foundations.
For non-structural walls, if their stability is guaranteed, cracking repair should achieve
the repair of other wall features – such as aesthetics.
The correct selection of repairing techniques for cracking of masonry walls should be
supported by a correct diagnosis, an extended identification and characterisation of the
cracks (their thickness, length, pattern, age, etc.) and also should be based on their
expected development. Many authors have established a check list for assessing
masonry cracking in order to assure an accurate diagnosis and repairing strategy [4.3-
4.6].
A main cause of masonry cracking is thermal movement and the stresses it induces.
This behaviour will be both cyclical and seasonal. Whatever the cause, cracks constitute
involuntary expansion joints [4.7]. In fact, most masonry cracks change over time, for a
variety of reasons:
− the crack reflects natural movements of the wall caused by temperature and
humidity variation;
− the cause is cyclic or acts randomly over time;
− the cause is permanent, persistent or increases over time;
− the edges of the crack are progressively destroyed by erosion or other physical or
chemical actions;
− the crack is progressively filled with particles, dust, salts, detritus etc.
The repair techniques for this situation are often aligned with one of these principles or
strategies:
− if there is a high level of internal thermal or moisture induced stress, the formal
creation of an expansion joint, instead of cracking repair, should be considered;
− if the transmission of forces and movements between crack sides is relevant,
fixing anchors or embedded steels bars should cross the crack;
− if the expected movements are reduced and become innocuous, but can affect the
final coating, a non-bonded strip repair should be used.
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A clear situation for cracking repair occurs when the water-tightness of the wall should
be restored. It is often necessary to enlarge the crack in order to get the ideal shape to
install a water barrier, like a flexible sealant strip (mastic), before repairing the crack. It
is essential to remember that the accuracy needed for the initial estimation of crack
width is much lower than when it is required for monitoring its evolution. Firstly, a
thorough visual inspection can distinguish between thin cracks (under 0,5 mm) and
medium (up to 2 mm) or large cracks, but their evolution cannot, in general, be
observed without precision equipment, able to detect and record 0,01 mm movements.
Table 4.1 - Monitoring techniques for masonry cracks
Name Description Specific notes
Gypsum mark
The gypsum mark crosses
the cracks. If the
mark is unbroken, the crack did not move.
If the crack has moved, the gypsum mark
will have cracked. Sometimes it is possible
to estimate the extension and direction of
the movement (low precision).
Recommended shape
5x50x100mm.
Pure gy
psum mixed with
water (70%). For outside
walls, lime and/or portland
cement are also used.
Glass mark
The glass mark is rigidly bonded on both
sides of the crack. The smallest movements
of the crack will break the glass mark.
Extremely fragile. It is
very
difficult to estimate the
extension and direction of the
movements
Paper mark
The paper mark is bonded to both sides of
the crack and breaks or gets wrinkled.
Only for large movements.
The results are quite
influenced by humidity
conditions.
Graduated ruler
(with or without
amplification lens)
The operator places the crack test ruler on
the crack and selects the width of the line
that corresponds to the crack opening.
Used only to estimate the
initial width of the cracks.
Precision less than 0,1 mm.
Optical micrometric
equipment
This device measures crack openings with a
hundredth of a millimetre precision.
The equipment includes an
internal graduated ruler or
scale and self-illuminated.
Paper gauges
Two plastic or paper graduated components
can slide one
over the other and clearly
show the extent and direction of
movements.
Very easy to use. Medium
precision. Affordable
solution.
Electrical gauge
Special strain gauges with different kinds
of filaments, eventually breakable. Any
small movement i
s detected and can be
automatically recorded.
As they are flexible, they
inefficient to detect width
decreasing of cracks.
Potentiometric
sensors
Several high precision methods
use this
kind of sensor. Reference
spots are placed
near the cracks and the distance
between
them
is measured with high precision
(0,002 mm).
The equipment can be hand
used periodically (hand
held
versions) or permanently
installed on the wall.
Digital calliper with
measurement base of
3 points (
stainless
steel)
The change in the d
istance between the 3
screws (measurement base) gives the
information to estimate the extent and
direction of crack movements with good
precision (0,01mm)
Useful for large or complex
movement monitoring.
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Facing brick masonry walls are quite unique, making their defects even more complex
to treat. Therefore choice of appropriate repair techniques must preserve the aesthetics
and colour, leaving little evidence of the repair.
The majority of defects in masonry walls can be repaired with standard techniques that
are quite efficient if they are supported by a correct diagnosis and clear strategy.
4.2-
B
RAZILIAN CRACKING REPAIR TECHNIQUES
15,16,17
4.2.1- Introduction
Masonry is a building construction system frequently used in Brazil, competing with
other ones such as reinforced and prestressed concrete, concrete walls, steel and timber
frames. The use of masonry is seen throughout the country, demonstrated by the
assorted types, shapes, materials, etc. The units are typically clay bricks or blocks made
of fired clay, concrete, calcium silicate, autoclaved aerated concrete and cement/soil.
Both reinforced and unreinforced masonry are used in buildings, usually with 140mm
thick single leaf walls. Masonry is also used for non-loadbearing walls, predominantly
made of fired clay or concrete blocks, competing with internal partition dry-walls,
generally with better sound and heat insulation properties.
Presently the Brazilian population is around 200 million inhabitants, with an estimated
housing deficit of 5.5 million. According to Corrêa [4.8], a study developed by the
Construction Community (2008) over three years and monitoring 200 Brazilian building
companies throughout the country, showed that the building sector (Civil construction
represents 16% of the Gross Internal Product) uses mostly reinforced concrete structures
(68%), while 20% represents the participation of structural masonry (Figure 4.2).
20%
68%
9%
1% 1%
Structural masonry
Reinforced concrete
Prestressed concrete
Pre-fabricated concrete
elements
Concrete walls
Figure 4.2 - Different structural systems used in Brazil
Roman & Antunes Silva [4.9] summarized the results of a wide range of research
studies in Brazil that have pointed out failures during the whole building process. Figure
4.3 shows the main causes of defects in Brazilian constructions.
15
Márcio Corrêa - Brazil
16
Ercio Thomaz - Brazil
17
Humberto Roman – Brazil
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Manag ement
20%
Design
11%
Tecn ics
17%
Planning
44%
Execution
8%
Technics
Techniques
Figure 4.3 - Causes of defects in Brazilian construction industry [4.9]
4.2.2- Prevention and repair
Different aspects of prevention and repair can be considered, since the problem is
complex and various and simultaneous causes may be identified. The most common
failures observed in Brazilian constructions are caused by: a) foundation differential
settlements; b) interaction with other structural elements; c) poor design and inadequate
execution procedures, and d) walls under roof slabs. The following tables summarize
both prevention and repairing techniques, with some examples of common solutions
applied in construction sites.
Table 4.2 - Prevention of damage and its repair related to foundation differential
settlements
Prevention Repair action
Evaluating soil parameters: increase the
geotechnical investigations
Observe dimensions and shapes of the
buildings: provide joints
Effect of: long dimensions in plan
view,
sudden change of shape, very different
loads, changes in soil and foundation types,
different construction periods of adjacent
buildings (Figure 4.4).
Attention to existence of soft/deep soil
layers, fluctuations of the water table and
leaking of t
he drainage system that
saturates the soil around shallow
foundations
Consolidation of soils and/or
increase
stiffness of foundation elements
Insertion of joints, allowing the building
parts to perform as independent rigid bodies
Use of deep foundation
when the water
table fluctuates or when there are soft/deep
soil layers.
Fix the drainage system.
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Plan view Plan view
(a) (b)
(c) (d) (e)
(a) One long dimension; (b) Change of geometry; (c) Different loading; (d) Building founded
on different layer depths; (e) Different types of foundation
Figure 4.4 - Joints to prevent cracks caused by differential foundation settlements
(adapted from [4.10])
Table 4.3 - Prevention of damage and its repair related to interaction between structural elements
Prevention Repair action
Limit deformation of materials and
beam/slab deflections to avoid high stresses
in masonry (design).
Separate structural elements and masonry
walls to discontinue stress flow.
Provide special building details in the
structural element/masonry interfaces
(Figures 4.5 and 4.6).
Include soft joints (Figure 4.7).
Increase stiffness of supporting elements
Relief of stress and introduction of resilient
materials between top of walls and base of
beams and slabs
Repair
detachment of masonry walls from
other interacting structures (Figure 4.8)
Repair or strengthen structural elements.
Steel mesh
Steel
rebar
Figure 4.5 - Typical details of interfaces between RC columns and masonry walls [4.11]
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Figure 4.6 - Typical details of interfaces between steel columns and masonry walls [4.11]
Φ 5 mm every even course
sealant
Soft
material
> 20mm
Figure 4.7 - Typical joint [4.11]
> 200mm
> 200mm
Old coating
Steel mesh
Old coating
RC column
New coating
Figure 4.8 - Typical repair of detachments of RC column and masonry walls (adapted
from [4.10])
140
3560
1402610
2210
140
140
1210
800
200
390
540
10
190
340
140
140
1210
1800
Dimensions (mm)
Odd course
Even course
Figure 4.9 - Walls in running bond – plan view
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Figure 4.10 - Last courses of partition walls of a multi-storey building
Concrete slab
Steel rebars
Completed after major shrinkage effetcs
Temporary joint
(breadth depends on splice length)
(at least 7 days)
Figure 4.11 - Temporary joint to reduce shrinkage effects on concrete slabs (adapted
from [4.10])
Last course to be filled
after top floor is built and
from top to base
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Table 4.4 - Prevention of damage and its repair related to poor design and inadequate
execution procedures
Prevention Repair action
Special care with production,
transport and storage of
materials. Special care with the characteristics of building
materials.
Precise specification of materials used, especially for the
mortar, as the mortar joint is the component that has the
greatest capacity to absorb deformations.
Proper compatibility of the properties of the masonry
components, with special attention to the use of units and
mortar with the modulus of elasticity as low as possible to
accommodate deformations.
Observe the modular coordination, preferably using a
running bond (Figure 4.9).
Use control joints and movement joints.
Provide lintels and sills with sufficient lateral penetration
and appropriate reinforcement. Special attention to the
tallest buildings, in particular the behavior of elements near
openings since they connect adjacent walls.
Special care with the transmission of loads between
successive floors (Figure 4.10).
Introduce appropriate construction details.
Special attention with tall buildings, where sealing masonry
often has an important
role to protect against horizontal
actions.
Removal and replacement
of damaged sections.
Eventual demolition of part
of the structural element to
substitute materials with
more suitable ones.
Introduction of additional
control joints.
Repair cracks.
Concrete
Slip joint
Lintel block
Soft material
grout
Concrete
Slip joint
Lintel block
grout
(upper course)
(upper course)
Figure 4.12 - Slip joints under roof slabs
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Table 4.5 - Prevention of damage and its repair related to walls under roof slabs
Prevention Repair action
Serious problem caused by shrinkage and/or
thermal movement of the roof slabs. This
is a very
serious problem in a tropical country such as
Brazil.
For the shrinkage of the slab, besides good curing
,
temporary joints can be inserted in the cast
slab
(later concreted) to reduce shrinkage
or permanent
joints can be placed in suitable locations
(Figure
4.11).
As for the thermal movement of the slabs, attention
should be given to minimize the causes such as
roof ventilation, shading of slab, painting the roof
top with white or reflective paint, thermal
insulation on the roof slab. Their effec
ts can be
minimized with the following measures: place
expansion joints in the slab, cast sliding joints in
the slab/wall interface (teflon, neoprene, double-
layer of PVC lining or strips of melamine material,
etc.) (Figure 4.12).
Use reinforcement on th
e top layers of the walls (in
support straps and/or reinforcement lo
cated in the
horizontal joints)
Subsequent insertion of expansion
joint in the slab, carefully cutting
and filling the empty space with
deformable material (Figure 4.13).
Implement
measures to mitigate the
causes (Figure 4.14).
Arrange additional horizontal
reinforcement along the upper
courses.
Repair the cracks (Figure
4.15).
by soft material
Cut part substituted
>20mm Concre te
Slip joint
Lintel block
gro ut
(up pe r course)
Figure 4.13 - Control joint
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S
hading
Ventilation
g
Insulation
g
Slip joint
Flexible joint Mesh inside
coating
Refle
c
tive
paintcoating
Figure 4.14 - Typical details for reducing the thermal effects on walls under roofs [4.11]
Steel mesh
> 30 mm
> 300 mm
Crack
Adhesive tape
New mortar fillingOld coating
Cotton twine
> 20 mm
Crack
Sealant
Mortar with acry lic resin
> 40 mm
Cotton twine
600 to 800 mm
Reinforcing steel
inserted in bed joints
Area of substituted units
Figure 4.15 - Repairing techniques (adapted from [4.12])
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4.2.3- Repair Methods
Deciding how the repair should be done depends on the cause of the problem and its
implications. The problem may be aesthetic or it could point to a serious structural
impairment. In any case, a well monitored inspection is required to stabilize the
problem. Having confirmed the stabilization, according to Page [4.13], three repair
methods can be chosen, summarized in Table 4.6. Note that these methods can be used
together depending on the problem at hand.
Table 4.6 - Repair Methods
Method Applicability Observations
Raking and
Re-pointing
Usually applied to cracks
localized in the mortar joints.
Effective for cosmetic reasons
only. Requires a skilled
bricklayer and correct
specification of a compatible
mortar.
Difficulty to completely fill the joint.
Long term shrinkage of fresh mortar
can cause cracking to re-
appear at the
same interface. The us
e of a polymer
modified cement mortar can allow
better penetration and bonding
characteristics. Special care should
be taken with facing brick masonry,
in order to preserve aesthetics.
Re-
construction of
Selected Areas
Usually applied to restore
structural integrity, including
demolition and re-
building of
the damaged area. Also
requires skilled tradesmen
and the correct specification
of materials.
Difficult to guarantee bond between
new and old masonry unless a control
joint is provided. The use
of a new
reinforced coating, when possible, is
recommendable.
Resin injection
Usually applied to cracks in
masonry units and to mortar
joints. Requires specialized
equipment and personnel.
Epoxy infection, despite the extra
cost compared with conventional
methods, provides mostly full
penetration and effective bond.
The resin must have compatible
stiffness to the repaired material, to
avoid local stress concentrations
under future movements.
Exposed resin must be resilient.
4.2.4- Case study
In some regions of Brazil, especially in the Northeast, some residential buildings are
built without frames. They are in general 4 storeys high and similar to structural
masonry, but with horizontally cored hollow blocks to both the walls and the
foundations. This has caused a very serious problem. Up to now, eleven of these
buildings have collapsed and more than 200 have been condemned (Figure 4.16 shows
two of these buildings).
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Figure 4.16 - Two types of the buildings which collapsed
Figure 4.17 illustrates the foundation of one of the buildings. These foundations
normally are from 0.4 to 2 m high and are normally built in a water saturated soil. The
water generally contains high levels of sulphates which increases the problem.
Figure 4.17 - Typical foundations of the collapsed buildings
Figure 4.18 shows one of the buildings after collapsing due to the foundation settlement.
Defects in Masonry Walls.
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Figure 4.18 - One of the buildings after collapse
Much research work has been done to establish the causes of the failures and also the
safety level of the remaining buildings. Signor and Roman [4.14] proposed a new safety
assessment methodology for the analysis of these buildings. Carvalho [4.15] has done
experimental and numerical research applied to one cracked building in Recife.
Dynamic, flat jack and acoustic emission tests have been conducted in the building.
Furthermore, tests were performed in laboratories on blocks, mortar, prisms, creep and
samples taken from the walls.
The main conclusion in both cases was that mortar rendering of the walls is crucially
important for the buildings of the metropolitan area of Recife, although they have not
been, nor should they be, designed with structural functions. This phenomenon, which
is real, might be masking problems arising in the design and construction of such
buildings.
Some attempts have been made to find ways to repair these buildings. The best one
seems to be the proposal to enclose the foundations within another reinforced concrete
system and to create a concrete framed structure to support the walls. This may solve
the problem, although it has proved to be very expensive in many cases.
4.2.5- Remarks
Identification, prevention and repair are mandatory to deal with defects in masonry
walls, always keeping in mind Grimm’s [4.16] recommendation: “Avoidance is the
goal. Control is the next best objective”.
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References
[4.1] PAIVA, V.; et al. (1985)- “Patologia da Construção”, 1º Encontro sobre
“Conservação e Reabilitação de Edifícios de Habitação” (in Portuguese), Documentos
Introdutórios, LNEC, Lisboa, Portugal.
[4.2] VICENTE, R.; SILVA, J. (2007)- “Defects of Non-Loadbearing Masonry Walls
Due to Partial Basal Supports”, Journal of Construction and Building Materials, 21 (11),
pp. 1977- 1990.
[4.3] BONSHOR, R.; BONSHOR, L. (1996)- “Cracking in Buildings”, BRE, Garston,
UK.
[4.4] THOMAZ, E. (1989) - "Trincas em Edifícios. Causas, Prevenção e Recuperação"
(in Portuguese), IPT/EPUSP/PINI, S. Paulo, Brasil.
[4.5] DRÈGE, J. et al. (1997) - "La pathologie des Ouvrages de Batiment" (in French),
Éditions WEKA, Paris.
[4.6] GRIMM, C. (1988) - "Masonry Cracks: A Review of the Literature", ASTM STP
992, American Society for Testing and Materials, Philadelphia.
[4.7] SILVA, J. (1998) - "Fissuração das Alvenarias. Estudo do Comportamento das
Alvenarias sob Acções Térmicas" (in Portuguese), PhD thesis, University of Coimbra,
Portugal.
[4.8] CORREA, M. (2012)- “The Evolution of the Design and Construction of Masonry
Buildings in Brazil”. Design Management and Technology, São Carlos, 2012, V.7, N.2,
p. 3-11.
[4.9] ROMAN, H.; ANTUNES SILVA, D. (2007) - “Typical Masonry Wall Enclosures
in Brazil”, In: CIB (2007) - “Enclosure Masonry Wall Systems Worldwide”, S. Pompeu
Santos (ed), Taylor & Francis/Balkema, London, UK.
[4.10] THOMAZ, E. (1998)- “Prevention and Repair of Masonry Cracks”, Journal of
Construction Technology, 37, pp.48-52.
[4.11] I.P.T. (2008)- “Clay Block Partition Walls - Good Practice Code”, Technological
Research Institute of São Paulo, Brazil.
[4.12] THOMAZ, E. (1979)- “Cracks in Buildings: Causes, Prevention and Repair”.
IPT/ Epusp/ Pini, São Paulo, Brazil.
[4.13] PAGE, A. (1993)- “Cracking in Masonry Housing”, Research Report N.
085.05.1993, University of New South Wales, UK.
[4.14] SIGNOR, R.; ROMAN, H. (2010) - “New Safety Assessment Methodology for
the Analysis of Masonry Buildings in Brazil”, 8th International Masonry Conference –
IMC, Dresden, Germany
[4.15] CARVALHO, J. (2010) - “Experimental and Numerical Investigation Applied to
a Building of the Metropolitan Area of Recife”, PhD Thesis, PPGEC-UFSC.
Florianopolis, Brazil.
[
4.16] GRIMM, C. (1997) - "Masonry Cracks: Cause, Prevention and Repair", Masonry
International, 10(3), pp. 66-76.
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5- Conclusions and Guidance to Prevent and Repair Cracking in Masonry Walls
5.1-
G
ENERAL
R
EMARKS
From the issues exposed and presented in Chapters 1 to 4, some general remarks can be
made:
• Masonry walls perform several roles in buildings: they can be structural or
infilling, enclosure or partition, they can have different finishes or be the final
finish and they may contribute to other functional requirements;
• The control of all functional requirements and the behaviour of masonry walls is
yet far from being perfect, taking into account the relevance of materials
properties and workmanship;
• The influence of regional practices, materials, and architectural solutions
increases the difficulty of global approaches - common for other building
components;
• Codes and standards, despite the important improvements made in recent years,
have few guidance on how to minimize serviceability problems such as
cracking;
• Among structural and non-structural solutions in a building, masonry is possibly
the one that is given less attention in undergraduate courses in architecture and
engineering despite its economic and functional importance;
• Probably the most common masonry defect is cracking. This defect has different
manifestations, between those that must be considered as unavoidable and only
with aesthetic implications, to those that are clearly unacceptable for aesthetic
and functional reasons. The range of accepted cracking defects is very different
in different cultures;
• Cracking repair depends on a correct diagnosis of the source of the movements
producing the cracks and if this movement is stabilized or not;
• Cracking repair is frequently not efficient. To achieve the repair objective a
strategic approach, methodology and technique should be adopted;
• It is important to consider that, due to the development of steel and concrete,
reinforced concrete structures are increasingly flexibility. This leads to an
increase in deflections and, therefore, an increase in cracking.
• Practices such as walls bearing on thin slabs, exclusion of mortar in vertical
joints, use of 10 mm thick mortar rendering and the use of brittle materials such
as rendering also have contributed to the appearance of problems with partition
and enclosure walls.
• A better understanding of masonry service behaviour and the capacity for
preventing defects needs more research - mainly experimental.
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5.2-
G
UIDANCE TO PREVENT CRACKING
Some design aspects, such as the positioning of movements and limiting deflections as
well as limiting tensile stresses, are key factors to prevent cracking. Also controlling the
relationship of masonry walls with other constituents and the execution of works can
help to decrease this problem. Therefore, some aspects are important to consider in the
design for Serviceability Limit State (SLS) of masonry:
• Partitions and enclosure walls on deformable supports (beams or slabs):
− The support (beams and slabs) of non-structural walls can require more
demanding deformation limits than the ones specified in structural codes and
should be established according to the quality of the wall and the presence of
openings for SLS combined loading (permanent, live and variable loading),
considering the long term effects (creep);
− Some acceptable deformation limits to help avoid cracking in partitions could be
(Figure 5.1):
i) deflection fb ≤ span/500 for walls without openings or with
constructive measures to avoid cracking;
ii) deflection fb ≤ span/1000 for walls with windows and doors;
iii) rotation θ ≤ 0,0017 rad;
Figure 5.1 – Recommended deformation limits
to help avoid cracking in partitions (fb is
the deflection affecting the behaviour of the partition after the construction of the
partitions)
− Non-structural and structural partitions and enclosure masonry walls should
be checked to ensure that tensile stresses are low (e.g. through a model
based on the uncracked masonry section, in which the tensile strength of
masonry can be considered);
− The use of low amounts of reinforcement for crack control is recommended
to increase the deformation ability of unreinforced masonry without
sustaining any visible cracking, given that severe deflection limits may be
unaffordable. (e.g. use of bed joint reinforcement in horizontal mortar
layers and mesh reinforcement renderings in general, near openings,
intersection of walls or other interfaces with other elements);
− The above measure can be combined with provision of joints at the
top/bottom of the partition/infill walls, in order to allow the deformation of
the support structure, without compromising the stability of those walls;
θ
f
b
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• Dimensional variations of the walls due to humidity or temperature:
− Movement joints should be designed by considering the different types of
phenomena (creep, moisture, thermal nature of masonry, reversible and
irreversible expansion) and masonry unit types (clay, concrete, AAC…), the
dimension of walls and relationship to other elements (e.g. near large span
openings or elements with different geometry);
− Reference values for the horizontal distance of movement joints should be
respected; these values can be increased by the use of reinforcement in the
bed joints and/or mesh reinforced rendering;
− The movement joints can be designed according to design codes or other
technical documents referred to in this document (e.g. the distance between
the movement joints is given in EN 1996-2 [3.9], according to the quality of
the masonry material, the presence or not of openings and bed joint
reinforcement in the wall);
− The thermal movements of the roof slabs must be carefully considered to
avoid common problems in the top floor walls, thus design procedures
should provide adequate construction details to avoid problems involving
thermal insulation of slabs by shading and/or reflective paintings,
introduction of control joints in walls, etc.;
• Relationship of masonry walls with other constituents:
− There is a difference between the properties of the support structure and
masonry partitions/enclosure walls (except for structural masonry). As a
consequence, a crack will occur at the interface of those 2 materials. There
are 2 solutions:
i) make a visible joint between the 2 elements;
ii) cover the joint, giving the possibility for the covered joint for
move (very important);
− The openings in the wall are weak points with concentration of tension in
the corners and the first cracks in case of a movement in the walls will occur
from the corners of the opening (this fact is well understood by engineers in
practice). Solutions to prevent this problem may include:
i) providing joint reinforcement at the corners - effectively
above the opening;
ii) in case of a door, in some countries (Belgium, Netherlands)
the opening continues till the upper part of the wall, dividing the
wall in two (in this case, there is no masonry corner anymore);
− Regarding structural masonry, tall buildings (e.g. in Brazil up to 70 m) may
cause high bending stresses related to out of plumb deviations due to
construction errors; also the adoption of rooms with spans from 6 to 8 m
without adequate stiffness and correct bearing details for the slabs has
produced bending moments in the masonry walls resulting in cracks in the
top region;
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• Execution of works
:
− Despite some trials with prefabricated masonry, masonry is still executed by
masons and has been for thousands of years. The quality of the masonry still
depends on the quality of the masons and their workmanship;
− Some practical concepts may help on site to help prevent cracking in
partitions or enclosure walls:
i) try to build the walls after the construction of the structure
so that a part of the structural deflection can occur;
ii) when walls are be built above each other on different levels
execute them on alternate levels (see figure 3.24);
iii) form a joint between the upper part of the wall and the
support so that the deformation of the support will not affect
the walls;
− These 2 methods avoid the increase of deformation on the lower levels, but
in any case the partitions must be constructed after removing the formwork
supports for the fresh concrete structure.
5.3-
R
EPAIR STRATEGIES
The prevention of problems is concerned with design, construction and workmanship
control procedures which are given in this manual.
Repair must always be based on a correct diagnosis of the real causes of each problem
seen. The aim should always be to restore the wall to its original condition.
No repair process should ever merely conceal or cover up the original problems – since
in time this might lead to a lack of structural safety or stability
5.4-
RESEARCH NEEDS
Some aspects of the behaviour of masonry in service (SLS) should be the subject of
research since there are no relevant recent studies in this area. Aspects that should be
thoroughly investigated by experimental testing and numerical simulations could be:
• Analysis of the effect of the support deformation on non-structural partitions and
enclosures, considering different materials and the use of reinforcement;
• Analysis of the behaviour of different interfaces masonry/support structures and
the influence of different connection systems for reinforced concrete and steel
structures;
• Numerical modelling of the mechanical behaviour of buildings with framed
structures and infilling masonry, considering different sequences of masonry
erection and the influence on the SLS.
11/11/2014
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