Seismic Assessment of AltoRio Building Collapsed in the Recent Earthquake of Chile, 2010

Abstract

This paper considers the seismic assessment of a 15-storey RC structural wall building, AltoRio,
located in the city of Concepción, collapsed in the M8.8 Chile earthquake, Feb 27th 2010. Different
methods of assessment, based on FEMA356, are applied to examine if the observed damage could

have been anticipated. Results show that FEMA356 assessment methods would have been identified
that the building was likely to be damaged in a major earthquake. Severe irregularities and discontinuity of walls in the base of the structure, in general, and lack of ductile detailing in walls and coupling beams are identified as the likely reasons for the damage. In addition to this assessment, the design procedures that are expected to have been used for the original design of the building are reviewed. The results showed that in applying the code design procedure, wall axial tensile forces were probably underestimated and improved capacity design procedures should be implemented.

Full text

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Seismic Assessment of a 15-Story Building Damaged in
the Chile Earthquake of February 27th 2010
M. Kohrangi
ROSE School, IUSS Pavia, Pavia, Italy
T.J. Sullivan
University of Pavia, Pavia, Italy
G.M. Calvi
IUSS Pavia, Pavia, Italy
SUMMARY
This paper considers the seismic assessment of a 15-storey RC structural wall building, Alto Rio,
located in the city of Concepción that collapsed in the M8.8 Chile earthquake of Feb 27th 2010. Different
methods of assessment, based on FEMA356, are applied to examine if the observed damage could
have been anticipated. Results show that FEMA356 assessment methods would have identified that
the building was likely to be damaged in a major earthquake. Severe irregularities and discontinuity of
walls at the base of the structure, in general, and lack of ductile detailing in walls and coupling beams
are identified as the likely reasons for the damage. In addition to this assessment, the design
procedures that are expected to have been used for the original design of the building are reviewed.
The results showed that in applying the code design procedure, wall axial tensile forces were probably
underestimated and improved capacity design procedures should be implemented.
Keywords: Seismic assessment, Chile earthquake, AltoRio building
1. INTRODUCTION
Seismic assessment of the Alto Rio building that collapsed in the Chile earthquake of 27th Feb 2010 is
provided in this paper. The earthquake was the sixth largest earthquake ever to be recorded. The
building was located in the city of Concepcion 100km from the epicentre of the earthquake. At the
time of the earthquake, 87 people were inside the building among whom eight people died and 79
survived (52 escaped on their own efforts, 27 were rescued) (Elnashai et al., 2010).
A number of buildings in the vicinity of the Alto Rio building were badly damaged by the very intense
and long shaking duration, but did not collapse like the building as shown in Figure 1.1. As reported
by (Elnashai et al., 2010), the building appears to have structurally failed at the connections between
the first floor and the two basements. Subsequent motions then caused the building to collapse on its
side as shown.
The question was raised whether the collapse of this building was caused by the large co-seismic
displacement that may have generated a global overturning of the building in a manner similar to
toppling of a chair when the rug under it is suddenly pulled away; or if the inertial earthquake forces

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that caused failures of other buildings in Concepción and elsewhere in Chile were the main cause of
the collapse. However, Alimoradi and Naeim (2010) showed that the co-seismic displacement was
most probably not the cause of the building collapse.
Figure 1.1 Picture of Alto Rio building before and after the Chile earthquake, Feb 2010 (Concepción under
Construction, 2010 left; El Periodista, 2010 right)
Investigating the latter type of collapse, which is the more probable type, is the purpose of this study.
In order to examine if the available code based assessment methods would have been capable of
anticipating the observed failure, a code based assessment according to FEMA356 is performed. Both
the Linear Static and Nonlinear Static analysis methods are applied in order to address the problem as
well as to gauge the applicability of the methods. In addition, in order to examine the reason why the
observed fragility of the building was overlooked in the original design, the design procedure that
might have originally been applied by designers of the building is reviewed.
2. DESCRIPTION OF THE STRUCTURE AND SEISMIC ACTION
2.1. Alto Rio Building
The Alto Rio building possessed two basements surrounded by retaining walls of thickness 25cm and
15 stories above the ground level consisting of shear walls with thickness of 20 cm, seen in Figure 2.1.
a)
c)
b)
Figure 2.1 Building geometry: a) Typical story plan, b) Most critical elevation (Elevation I) with wall discontinuity to
the foundation, c) Typical wall cross sections (e.g. W8-1 and W20-1)
Discontinuous walls
in the first level
Wall discontinuity to the foundation
X
Y
W8-1
WI-1
W5-1
WI-2
WI-3
WI-4
W20-1
W5-3
Transfer beam

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The story height was 252cm, except for the first storey which was 306cm. The floor system is concrete
two-way slab with 15 cm thickness. The typical building plan and what the authors consider to be the
most critical building elevation are shown in Figure 2.1. In the X direction, the system is more a
coupling wall system with strong beams that connect the walls. In the Y direction, two single walls in
each elevation form the structure. In this direction, the connection of slabs to the wall is expected to
have provided a coupling effect between the walls.
The structure is irregular in height because over the upper stories (12 to 15) it is set back in plan (see
Figure 2.1). The plan of the structure in the underground levels is rectangular with dimensions of
45.6x22.8m whereas the typical stories above the ground level have plan dimensions of 39.3x11.8m.
2.2. Seismic Action
Forthisstudy,agroundmotionrecordedinstation“Colegio San Pedro de la Paz”8kmawayfromthe
epicenter of the earthquake and 102 km away from Alto Rio building has been used. The location of
the building with respect to the epicenter and record station are shown in Figure 2.3.
Figure 2.2 Response and Design spectra according to
Chilean seismic code
Figure 2.3 Location of Colegio San Pedro de la Paz
station with relation to the site (Google earth)
Two response spectra of the records in the perpendicular directions (named as X, Y) are compared
with the design spectrum of the Chilean code (NCh-433/96) in Figure 2.2. In calculating the design
spectrum for this study, zone 3 with soil type III according to the Chilean seismic code is considered.
An interesting observation is that the design spectrum of NCh-433/96 matches closely with the
response spectrum obtained from a recording of the earthquake 8km from the site. The 27 February
2010 event could be considered a design intensity scenario for the city of Concepcion.
2.3. Modeling assumptions
SAP2000 (computers and structures, 2010) is used in order to conduct various analyses of the
building. A 3D model is developed for the modal and linear analysis. Nonlinear Static Analysis is
performed for two separate 2D models for the X and Y directions. For modelling the wall elements
and the coupling beams, frame elements are used and each element is positioned at the centroid of the
section. The cracking effect in RC elements was taken into account by a reduction factor of 0.5 of the
cross section stiffness (0.5Ec Ig). It is noted that more accurate estimates of the cracked stiffness could
be obtained (see Priestley et al. 2007) but the 50% reduction was adopted here as an approximation
that was considered reasonable given the other arguably greater uncertainties in the seismic
assessment. A global view of the 3-D model in SAP2000 is shown in Figure 2.4.
0
0.5
1
1.5
2
2.5
0 1 2 3 4
Sa [g]
Period (Sec)
X Direction
Y Direction
Chilean Code, SOIL III

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In order to take into account the effect of intersecting walls acting as T-shape, L-shape and U-shape
sections, the vertical beam elements (walls) are linked together by rigid arms (rigid link beams) at
each floor level. It is important that these rigid arms are modeled with the properties that are relatively
rigid in the plane of each wall panel but not out of plane. To achieve this, a reasonable starting point is
to assume that the rigid arm properties are based on a section with depth equal to the floor to floor
height or vertical spacing of rigid arms and thickness equal to that of the wall, and then adjust the
properties of the rigid elements as follows (in line with the recommendations of Arnott, 2005): 1) Ix-
Torsion constant (out of plane effects) is reduced by a factor of 10 and 2) Iy- In plane stiffness is
increased significantly by a factor of 100.
Figure 2.4 3D view of the model in SAP2000
The coupling effect of the slabs and the beams with T shape cross section are not considered in the
modeling. The building in the underground levels is surrounded by retaining walls with a thickness of
25 cm and therefore the retaining walls up until ground level would provide a relatively rigid support
for the structure. As such, in the model the first two stories are laterally restrained.
3. Analysis Results
From Eigen value analyses of the structure model described in the previous section it is found that the
first mode of the structure is translational in the X direction (longer side) with a period of 1.09s. The
second mode is translational in the Y direction (shorter side) with a period of 1.07s and the third mode
is determined as rotational with a period of 0.83s. The relatively short periods of the 15-storey
structure obtained from the modal analysis are typical of the constructional practice in Chile
(Boroschek, 2010), since by the application of many structural walls, the stiffness of structures in
Chile tends to be very high and consequently short periods are observed.
3.1. Linear Static Procedure
According to FEMA356, the pseudo lateral load in a given horizontal direction of the building is
calculated according to the following equation.
   (3-1)
The values of the coefficients  are defined according to FEMA356 and the definition of
each one can be found in the code, Sa is the spectral acceleration and W is the total weight of the
building. For the current structure, the base shear is calculated using the following coefficients: C1
=1.0, C2 =1.0, C3 =1.0, Cm =1.0, Sa = 0.68.

5
The deformation controlled actions of each element can be calculated as follows:
  (3-2)
In which,  is the design action due to gravity loads and earthquake loads,  is the action due to
the design earthquake loads and  is the action due to design gravity loads. Therefore, the Demand
Capacity Ratio (DCR) for the deformation controlled actions can be calculated according to the
following equation:
  
 (3-3)
In which,  is the Component or element demand modifier (factor) to account for expected ductility
associated with the action at the selected Structural Performance Level which is an indirect measure of
the nonlinear deformation capacity of the component or element. The m factors are adopted from
FEMA356 considering the CP (Collapse Prevention) limit state (and are shown later in Table 3.1). k is
the knowledge factor which for the case of the current structure is considered equal to one, finally,
 is the Expected strength of the component or element.
On the other hand, force controlled actions, , can be calculated using a number of methods. It shall
be taken as the maximum action that can be developed in a component based on a limit-state analysis
considering the expected strength of the components delivering load to the component under
consideration, or the maximum action developed in the component as limited by the nonlinear
response of the building. Alternatively, , can be calculated according to the following equation:
  
 (3-4)
In which  is the action due to the design earthquake loads and  is the action due to design gravity
loads. C1, C2 and C3 are the values defined in FEMA356 which are the same as indicated in Eq. (3.1).
J is a Force-delivery reduction factor, greater than or equal to 1.0, taken as the smallest DCR of the
components in the load path delivering force to the component in question. Alternatively, values of J
equal to 2.0 in Zones of High Seismicity, 1.5 in Zones of Moderate Seismicity, and 1.0 in Zones of
Low Seismicity shall be permitted when not based on calculated DCRs. In this study, a value of J=2 is
used. According to FEMA356, in the case of concrete structural walls, moment and shear actions are
considered as deformation controlled actions and axial load as a force controlled action. However, in
the case of concrete beams, only moment is suggested to be deformation controlled and shear should
be considered as a force controlled action.
The results of Linear Static Assessment are shown in Table 3.1. The name of each wall and beam was
indicated earlier in Figure 2.1. The results indicate the evaluation of the wall sections in the first floor
of the building, where the formation of plastic hinges and expected failure is more likely to occur. The
analysis is performed for both positive and negative directions and the results for the most critical
cases are shown here. The main problem observed in the wall sections in the X direction emerges from
the axial tension forces developed in the coupled walls. For example, in walls WI-1 to WI-4, the axial
tension demand coming from earthquake and gravity loads are higher than the maximum axial tension
capacity of the wall calculated using the longitudinal reinforcement indicated in construction
drawings. The tension yielding of the reinforcing bars could cause significant bar elongation and
probably, in the next cycle of oscillation, the reinforcing bars would then have experienced a buckling
failure in compression leading to the failure of the whole section. In some exaggerated cases, the
tension force in the wall is so high that the rupture in the reinforcing bars is likely which can be
considered as the wall failure. On the other hand, even for the cases where the axial tension demand

6
doesn’t surpass the axial tension capacity, the flexural capacity of the section reduced to very low
values.Thesameissueisobservedforthewallsinelevation“A”and“C” where, similarly, the walls
are not continuous into the foundations.
Table 3.1 Results of Linear Static Analysis According to FEMA356
Demand1
Capacity
Demand/Capacity (DCR)
Wall Name
P 6
M
V
P2
M 3
V 4
m
P
M
V
W-I1
6417
3245
1148
1577
0
853
2.0
3.9
NC 5
0.7
W-I2
1924
1357
1576
1493
0
694
4.0
1.1
NC
0.6
W-I3
2233
3122
1229
1493
0
788
2.0
1.3
NC
0.8
W-I4
1928
534
487
874
0
265
2.5
1.9
NC
0.7
W5-1
2278
790
144
937
0
338
2.0
2.2
NC
0.2
W5-3
1840
874
282
937
0
338
2.0
1.7
NC
0.4
W8-1
-50
28815
1578
2541
13396
2594
3.0
-
0.7
0.2
W20-1
-68
25267
2546
2541
14550
2695
3.0
-
0.6
0.3
1- Axial load, moment and shear demands derived from linear analysis (kN, kN. m)
2- Maximum axial tension capacity of the wall
3- Maximum moment capacity of the wall corresponding to the axial load derived from moment-axial load interaction curve
4- Shear capacity of the member according to ACI-318-02
5- NC=No moment Capacity due to excessive axial load
6- Positive values are tension and negative values are compression
For the walls in the Y-direction, in elevations 8, 13, 20, 26, 34 and 35, which have two walls of length
540 cm without many effective discontinuities and irregularities, the values of DCR for flexure and
shear are less than 1.0 except for the walls in elevation 5. For example, in walls W8-1 and W20-1, the
expected seismic axial forces are very small and thus negligible. Even though minimum shear
reinforcement was typically provided to the walls, it was found that for the walls under consideration
in the first floor there were only three cases in which a shear DCR of higher than 1.0 is observed.
Therefore, it can be concluded that the occurrence of shear failure should not be expected to have
preceded the axial-flexural failure of the examined cases.
3.2. Potential impact of the Chilean Code on the design of the Alto Rio Building
In order to examine the probable design procedure that was used for the original design and
construction of the building, a code based design approach is adopted in this section and then
comparisons are made with FEMA356 linear assessment method. Chilean seismic code (NCh043,
1996), suggests a Modal Response Spectrum analysis method rather than linear analysis for structures
higher than 6-stories. Therefore, in the following, the MRS method has been applied for the analysis
of the structure as this is likely to have been the method used for the design of the building. The design
spectrum according to NCh-043 can be derived as follows:

 ,  


 (3-5)
In which, Sa is the design spectral acceleration, I is the importance factor which for the residential
buildings can be considered equal to 1.0. A0 is the maximum effective acceleration according to the
national seismic zoning. For the city of Concepcion (zone 3) A0=0.4g can be considered, α is the
amplification factor which accounts for the spectral shape. In which, Tn is the vibration period of mode
n, T0 and p are parameters relative to the foundation soil type. According to NCh-043, these values can
be assumed equal to 0.75 and 1.0, respectively. R*, is a reduction factor that for structural wall systems
can be calculated as follows:

7
   
 (3-6)
In which, N is the number of stories and R0 is a modification response factor. For structural wall
buildings a value of 11 is suggested for R0. Using N=15 and T0= 0.75, a value of R*=4.43 is obtained
and with the application of the design spectrum an MRS analysis is performed. The two load
combinations of       adopted from ASCE7-05 were observed to be the most
critical load cases and thus the results of these two load combinations are reported in Table 3-2. The
last three columns in the table show the capacity over demand ratio of the walls in shear and flexure.
Table 3-2 Simulated design summary of walls I-1 to I-4 and 5-1 to 5-4 according to Chilean code, NCh-043
Wall
Name
PD, T1
PD, C2
MD3
VD4
MN, T5
MN, C6
VN






WI-1
1692*
-3270
843
266
0
3374
872
0.0**
0.28
0.40
WI-2
47
-1137
933
422
4234
4550
678
0.24
0.23
0.83
WI-3
27
-1193
185
327
355
630
702
0.59
0.32
0.63
WI-4
220
-1471
149
146
264
670
436
0.63
0.24
0.45
W5-1
216
-1018
133
118
244
550
387
0.63
0.27
0.40
W5-3
118
-920
219
123
255
560
395
1.00
0.43
0.42
1-Axial load, load combination U2, kN
2-Axial load, load combination U1, kN
3-Design Moment, kN. m
4- Design shear force, kN
5-Nominal moment resistance for load combination U2, kN. m
6-Nominal moment resistance for load combination U1, kN. m
* Positive values are tension and negative values are compression forces
** Axial tension force exceeds the axial tension capacity; therefore, no flexural resistance is expected.
As can be seen, except for the case of wall WI-1, the ratio of demand over capacity is less than one.
This general trend could raise doubts as to whether a force reduction factor of 4.4 was actually adopted
because if it had been, one could expect the demand to capacity ratios to equal 1.0. However, lower
values may be indicative of the typical practice of providing more strength than necessary when sizing
reinforcement and seeking standardized construction details. Note also that in the linear assessment
procedure of FEMA356, the m factors suggested for the consideration of the nonlinear behavior of the
wall elements were in range of 2-2.5 for most of the cases, which does appear to match the
construction solution well. This value (R*) is used to reduce all actions consisting of axial load,
moment and shear.
As it was mentioned before, according to FEMA356, the axial load action in the structural walls is
considered force-controlled and therefore it is suggested to reduce the axial force coming from
earthquake by a J=2 factor for assessment of the element. As it was observed in Table 3.1, in most of
the critical walls, the axial tension load demand exceeds the capacity and consequently results in zero
moment capacity. However, in the design procedure, all of the actions- axial load, moment and shear,
coming from the earthquake w ould be reduced by a factor of R*=4.43. This would lead to a significant
reduction in the tension axial load on walls in design compared to the axial loads predicted from the
FEMA356 assessment approach. This highlights an issue with the design approach since it is evidently
not conservative to assume that flexural strength can be set greater than the design flexural demand
without also checking the consequences on the strength-dependent actions, such as axial forces. This
reflects a potential shortcoming with the capacity design procedures used in the design of the Alto Rio
building, since a rigorous capacity design approach (see, for example, guidelines provided in Priestley

8
et al. 2007) would have established peak axial forces based on the strengths provided to potential
plastic hinge regions.
An alternative explanation for the apparent underestimation of axial forces may have been an error in
interpreting the axial forces obtained from modal response spectrum analysis in which computer
software makes a combination of axial force computed and reports the absolute values. Without care,
the SRSS or CQC axial forces may be interpreted as forces in compression rather than tension. As the
bending resistance of RC walls greatly reduces when walls are subject to tension, it is apparent that
this could be a reason for the poor seismic performance observed of the building.
It is worth mentioning that FEMA356 suggests m values of 4 and 6 for concrete structural walls in
collapse prevention limit states for the cases in which a confined boundary element is provided for the
section and the axial compression force is less than 0.1 and 0.25 f’c Ag, respectively. However,
appendix B of the Chilean seismic code explicitlymentionsthat“When designing reinforced concrete
walls, it is not necessary to meet the provisions of paragraphs 21.6.6.1 through 21.6.6.4 of the ACI
318-95 code.” This part of the code is about the consideration of the confinement and boundary
elements for the walls in high seismic zones and as was mentioned before, in the design of the current
structure, very little confinement and no boundary elements were provided for the wall sections,
which may also have been a critical factor in the building failure.
3.3. Nonlinear Static Procedure
The nonlinear static (pushover) procedure of FEMA356 requires definition of the nonlinear load
deformation relations according to the tables provided in this code. For each wall and beam section in
each story, the moment-axial load interaction is derived using CUMBIA [Montejo and Kowalsky,
2007] and two moment-axial load hinges have been defined for two ends of the elements. In addition,
shear strength is calculated according to ACI-318-02 and brittle shear plastic hinges are defined in the
middle of each wall or beam element. The capacity curve of the structure is derived based on a modal
load distribution. Thetargetdisplacement,δt, at each floor level is calculated in accordance with the
following equation:
 

 (3-7)
 are modification factors defined according to FEMA356, Sa is the spectral acceleration
and Te is the effective fundamental period of the building. The values of target displacement demands
for two orthogonal directions have been derived equal to 0.26m and 0.43m for X and Y directions,
respectively. In Figure 3.1 pushover curves are depicted. In addition, the stage in which the first
element reaches the predefined local limit state is shown. For the X and Y directions the first elements
that pass the limit states are WI-4 and W5-1, respectively.
In the X-direction, as it was also suggested by the linear static analysis, the wall elements that suffer
most are the ones that are subject to high axial tension loads especially in the first storey of the
building. On gridlines “I”and“A” (see Figure 2.1a), because of the coupling behavior of the walls, the
axial load has exceeded the axial tension load capacity of the walls in the first storey. Whereas, the
walls that have been subject to axial compression, have rarely passed the LS (Life Safety) limit state.
Assuch,attargetdisplacement,mostof thewallsin thefirststoryinelevation“I”and“A” passthe
CP(CollapsePrevention)limitstate.Thisfactisalsoobservedforthetransferbeamsinelevation“A”
and“I”inwhichmostofthebeamspassintothe CP limit state.

9
Figure 3.1 Pushover curves of the structure for X and Y direction
In the Y-direction, at the target displacement all of the walls on gridlines 8, 13, 20, 26, 34 & 35 (see
Figure 2.1a), have remained in the IO (Immediate Occupancy) limit state except in one case at the
second storey of grid 8, where the LS limit sate is reached. In this direction, only the walls at the base
of the second storey of grid 5 exceed the CP limit state due to high axial tension forces. Shear hinges
were not observed in both directions except for a fewcasesin elevation“A”and “I” inwhichshear
plastic hinges reached the IO limit state. In addition, some of the coupling beamsinelevations“A”
and “I” developed shear hinges but demands did not exceed the IO limit state. According to these
analyses, in the X-direction of the building in which there are severe irregularities over the height of
the structure, more damage is predicted and is concentrated inelevations“A”and“I”.In contrast, all
the structural walls in the Y-direction, except those on grid “5”,successfullysatisfytheLSlimitstate.
These observations would suggest that failure of the building was expected in the X direction.
However, the photos of the building after collapse suggest that the collapse occurred in the positive Y-
direction (refer Figure 2.1a). Although severe damage and failures could have been predicted in the
structure on grids “I” and “A”bytheassessmentprocedure, it mightbequestioned:“how can these
results explain the collapse of the structure in the Y-direction?”Oneprobable scenarioisthat,if the
building experienced significant damage to the four walls of WI-1, WI-2, WI-3 and WI-4 and the
transfer beams of BI-2, BI-5 and BI-6 (see Figure 2.1) of the structure on grid I the gravity load
carrying capacity along this side of the building could have been lost, provoking the collapse of the
building in the Y-direction, in a manner like removing two legs of a chair on one side.
4. CONCLUSIONS
The seismic assessment of the Alto Rio building that collapsed in the 2010 Chile earthquake has been
undertaken. The building is located in the city of Concepcion, Chile. Assessment has been carried out
using linear static and pushover analyses based on FEMA356. The assessment methods confirm that
the building should not have been expected to be able to sustain the seismic shaking, which
interestingly, appears to have been of a similar intensity to the code design spectrum. In light of this,
efforts have been made to consider how the Chile design practice may have provided the building with
insufficient resistance. It is hypothesized that the designers may have underestimated the large tensile
forces that can develop in walls due to coupling actions. Reasons for this may be related to poor
interpretation of modal analysis results or inadequate capacity design procedures.
Interestingly, while common pushover analyses of a 15 storey building could often be considered of
limited value, since they do not account for the higher mode effects, the building under examination
0
2000
4000
6000
8000
10000
12000
0 0.1 0.2 0.3
Base Shear (kN)
Top Displacement (m)
Pushover curve (X-direction)
0
2000
4000
6000
8000
10000
12000
0 0.2 0.4 0.6
Base Shear (kN)
Top Displacement (m)
Pushover curve (Y-direction)
IO
LS
CP
CP
LS
IO

10
was so stiff that it is expected that higher modes did not play a significant role in the response. This
was supported by the results of modal analyses. It is also interesting that because of Chilean design
and construction practice, the large number of walls in the structure would suggest that the seismic
demand should not be excessive in the walls. However, because of the discontinuity and irregularity of
the walls in the first storey of the building that have caused concentration of demands on the
remaining walls, shear and flexural demands would have exceeded the capacity in the walls of this
storey which could have led to the failure of the entire building.
In closing, while these analytical studies have identified some possible reasons for the observed
damage, the actual behavior of the complex structural system used for the building cannot be known
with certainty and other reasons for the damage (such as soil structure interaction effects, poor
construction detailing, etc) should also be considered as part of future research.
AKCNOWLEDGEMENT
The authors would like to thank Professor Patricio Bonelli for providing the drawings and other
important information about the Alto Rio building required to proceed with the assessment of the
building. In addition, the second author acknowledges support of the RELUIS project.
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