FIGURE 6 - uploaded by Habib Tabatabai
Content may be subject to copyright.
Source publication
NCHRP Project 10-53 - Phase I Report
This report contains the findings of a study performed to determine whether a practical and economical method for quantitative nondestructive condition evaluation of bonded prestressing systems in highway bridges exists. The report provides a comprehensive summary of a global technology review made to identify N...
Context in source publication
Context 1
... brief reference is made to ongoing tests on concrete specimens. Each of the two MsS sensors consist of a coil that encircles the reinforcing bar or strand and a bias magnet that creates a biasing DC field, as shown in Figure 6. This technique is based on the principle that a magnetic material changes its shape when subjected to a changing magnetic field. ...
Similar publications
This paper reports the outcome of a study on the resilient modulus of hot mix asphalt characterised under different environmental conditions and testing methods with the intention of establishing the effects of climate and testing procedure for appropriate standardisation of laboratory and field quality control/assurance of pavement works. Destructi...
Objetivou-se com este trabalho avaliar o consumo, a síntese de proteína microbiana e o balanço de nitrogênio em cordeiros alimentados com rações contendo 0,00; 12,50 e 25,00% de feno de amoreira em substituição ao concentrado. Foram utilizados vinte e quatro cordeiros Ile de France, com aproximadamente 60 dias de idade e 15,48 ± 0,07 kg de peso cor...
In the field of civil engineering, the survey of the thin top layer of carriageways, i.e. the pavement layer, is hardly performed by the conventional radar Non Destructive Techniques. This thesis aims to improve the time resolution of the classical GPR radar by a factor of 3 at least, using super and high signal processing techniques applied to tim...
Citations
... MOE modulus of elasticity, T temperature, H humidity in percent investigated, ultrasonic guided waves (particularly for anchorage zones) [55,56], magnetic flux leakage inspection and acoustic emission monitoring appear to be suitable [57,58]. High-frequency electromagnetic methods (ionizing methods, such as radiography [59,60], or non-ionizing, such as radar or time-domain reflectometry [61]) are also applicable in principle. Work related to ropes deals with wave propagation into cylinder or cylinder-like structures, including strands, using mono-elemental magnetostrictive-and/or piezoelectricbased devices in pulse-echo and through-transmission mode [62][63][64]. ...
Extension of the life of existing and historic timber structures has increased steadily in the last decade. Sustainability and low carbon emission have influenced activities in the construction industry. In the frame of the European COST Action FP 1101, several activities related to timber structures have been clustered. The COST Action FP 1101 consists of three working groups, namely Assessment (Working Group 1), Reinforcement (Working Group 2) and Monitoring (Working Group 3) of Timber Structures. This special issue of the Journal of Civil Structural Health Monitoring gives an overview of timber structure monitoring activities mainly from a European perspective. This paper is an introduction to this special issue and gives an overview of monitoring concepts and applications related to non-destructive testing (NDT). The prime intention is to give contextual crosslinks to other fields in which NDT methods and monitoring principles have already been developed so that synergies can be realized for timber structures. Outside urgent structural safety issues, monitoring of timber structures has the potential to become a state of the art technology for which material models and NDT-based sensors allow a design criterion for an optimized and highly efficient use of said structures. The sensor concepts may further be enhanced, however, with possible lower cost alternatives in terms of sensors and electronics.
... However, it requires appropriate amplifiers and pre-amplifiers as well as sophisticated data processing and filtering to discriminate the weak AE signal from the ambient noise [22] . Guided wave ultrasonic testing (GWUT) [12][23][24][25] and time-domain reflectometry (TDR) [26][27][28] might be challenged by signal attenuation at deviators and end anchorages. Other wave propagation methods, such as impact-echo (IE) or ultrasonic testing (UT) impulse-echo are also not found suitable for tendon monitoring as IE test results can be significantly influenced by the cracks and other concrete defects, and UT can detect tendon faults only within a short distance from the PT anchorage [29][30] . ...
Post-tensioned segmental bridges are common throughout the US; however, in recent years, the incidence of tendon failure in bonded post-tensioned bridges has raised questions regarding their design, construction, and maintenance. These failures have led to the investigation of the applicability of using replaceable unbonded tendons in segmental construction and new methods for monitoring their condition. This paper presents a damage detection algorithm to identify strand breakage in unbonded tendons based on the relative variation of strains in the anchorage. In unbonded construction, the anchorage assembly usually undergoes a severe stress-state condition as the entire prestressing force only passes through the deviator and end anchorage locations. The strain distribution in the anchorage mechanism, therefore, goes through significant changes in response to the breakage of an individual wire or an entire strand in a multi-strand arrangement. In this way, breakage of a post-tensioning strand can be identified by observing a non-uniform variation of the strain field over the anchorage region in contrast to a uniform variation of strains due to environmental or traffic loading. A reduced scale laboratory experiment is performed followed by an extensive finite element simulation to conduct a parametric study with wire/strand breakages at different locations on multi-strand anchorages commonly used in industry. Based on the observed strain variations from simulation, a damage detection model is proposed that enables the adoption of an automated monitoring strategy to characterize the breakage programmatically.
... Among the diverse investigated techniques, ultrasonic guided waves (particularly for anchorage zones) [8][9], magnetic flux leakage inspection, micromagnetic methods, and acoustic emission monitoring appear to be suitable [10][11]. High-frequency electromagnetic methods (ionizing method as radiography [12][13], or non-ionizing as radar or time-domain reflectometry) were rejected in this case due to the time-consuming nature, radiation hazards and low material portability of the first one, and the screening effect of metallic pieces for the two last ones [14]. ...
Infrastructure is subject to continuous aging. This has given life cycle management of infrastructure an increasing role. Reliable inspection and monitoring tools are therefore increasingly requested. A reliable prognosis of the condition and behavior of a structure is an important basis for an effective service life management. Furthermore, traffic loads and also loads due to changing environmental conditions (wind loads due to climate change, increasing water levels at the sea etc.) increased during the last years and will increase in the future. Repair and maintenance have to be performed which requires reliable concepts and reliable measurement data preferably gained with non-destructive methods. Furthermore, infrastructural constructions often have to be reconditioned when they are in use i. e. they cannot be torn down and build up new. Therefore, reliable diagnosis of the state of ‚hot spots‛ is required. In frame of the Franco-German project FilameNDT steel wires of external tendon ducts and prestressing strands, prestressing rods and stay cables are investigated. Regarding this field of application practical relevance can only be gained when easily applicable and long ranging methods can be used. Therefore, a global and a local approach were chosen. The evaluation of extended structural elements using non-contact movable systems (bulk wave and guided wave application (Piezo, Electro Magnetic Acoustic Transducers (EMAT)), Magnetic Flux Leakage (MFL), Micromagnetic methods) and that of localized elements based on elastic guided wave propagation – are complementary since they can be applied according to the various accessibility conditions of the tested objects. Inspection and monitoring scenarios were developed, hot spots identified and lab tests as well as field tests were carried out. The NDT methods were applied for inspection and used for monitoring on-site tests. A real wire rope bridge in the Saarland region is provided for monitoring tests and micromagnetic as well as acoustic monitoring systems are applied in frame of the project. The overall result is a know-how gain related to the developed advanced NDT techniques for the use in the inspection and monitoring of civil structures. The different scenarios and results will be presented discussed. Furthermore, the experience is presented describing in detail the reliable and qualified application and verified results which can be transferred to a service inspection and monitoring.
... Numerous applications of non-destructive tests, such as an ultrasonic test and a pulsed eddy current test, have been used to evaluate prestress force on bonded and unbonded tendons. Such non-destructive tests have been shown to have several problems-for instance, weakened signal detection due to the use of concrete and grouting materials, and difficulties related to the installation of a sensor on the tendon embedded within the structure [3]. Thus, technology is being developed to analyze the loss of prestress force and to predict prestress force through the SI technique, which uses the dynamic characteristics, strain, or displacement of the structure according to the prestress force [4][5][6][7][8][9][10][11]. ...
Bonded tendons have been used in reactor buildings at some operating nuclear power plants in Korea. Assessing prestress force on these bonded tendons has become an important pending problem in efforts to assure continued operation beyond their design life. The System Identification (SI) technique was thus developed to improve upon the existing indirect assessment technique for bonded tendons. As a first step, this study analyzed the sensitivity of the key parameters to prestress force, and then determined the optimal parameters for the SI technique. A total of six scaled post-tensioned concrete beams with bonded tendons were manufactured. In order to investigate the correlation of the natural frequency and the displacement to prestress force, an impact test, a Single Input Multiple Output (SIMO) sine sweep test, and a bending test using an optical fiber sensor and compact displacement transducer were carried out. These tests found that both the natural frequency and the displacement show a good correlation with prestress force and that both parameters are available for the SI technique to predict prestress force. However, displacements by the optical fiber sensor and compact displacement transducer were shown to be more sensitive than the natural frequency to prestress force. Such displacements are more useful than the natural frequency as an input parameter for the SI technique.
Knowledge of prestressing force’s value is in the case of prestressed concrete structure the most important basis for defining load-carrying capacity and remaining service life. Numbers of prestressed concrete structures are about to reach their limit of service life and they are exhibiting signs of deterioration due to the conceptional errors, inadequate maintenance and environmental distress. All of these factors negatively influence the actual state of prestressing. Thus, it is essential to determine the value of prestressing force considering the degradation of materials, such as corrosion of prestressing strands or wires. While assessing structure in service, it is difficult to apply magnetoelastic sensors or use other direct methods for determining the state of prestressing. Hence, the indirect methods enable to analytically calculate the prestressing force based on the results of measurement, e.g. strain, stress, deflection, or width of the crack. The present paper focuses on numerical analysis of prestressing in a twosome of precast prestressed concrete beams. For the numerical analysis, two indirect methods are applied, specifically Saw-cut method and Crack initiation method. Finally, the results are discussed and recommendations for the experimental campaign are summarized.
In Slovakia and other countries, a contemporary challenge for engineers and academics is an assessment of the state of existing prestressed concrete structures. The main components of assessment include regular inspections, maintenance, and diagnostics. For defining the load-carrying capacity and remaining service life, more reliable results of diagnostics are required. A need for detailed knowledge of the actual value of prestressing force is becoming a crucial aspect of civil engineering. There are many prestressed concrete structures built in the previous century which are about reaching their limit of service life. These structures are about sixty years old and many of them are exhibiting signs of deterioration due to the design and construction deficiencies, such as overloaded vehicles, environmental distress, and inadequate maintenance. In this paper, dozen concrete specimens are numerically analysed using the indirect non-destructive Saw-cut method. Ten of them are loaded by different level of compressive force which initiates compressive stress from 2.0 MPa to 12.0 MPa. Performed numerical analysis is an important basis for the experiment. The influence of temperature change caused by sawing will be later experimentally investigated on the remaining two concrete specimens. For numerical analysis, a 2D finite element model with the assumption of nonlinear material behaviour is performed. Subsequently, the correlation between the distance and depth of the saw-cuts, and amount of released strain or stress, as a result of numerical analysis, is outlined. Finally, the outputs obtained from numerical analysis are discussed and recommendations for the experiment are summarized.
This work introduces a non-destructive experimental technique to evaluate the existing prestress level on bonded tendons embedded in a post-tensioned concrete structure. By measuring the longitudinal stress wave velocity on the strands, the applied stress level can be evaluated using an experimental formula. The experimental relation between the applied stress levels and the stress wave velocity is derived from various impact-echo test results for a set of prestressed concrete beam specimens with different tensile stress levels. The experimental results reveal that the longitudinal stress wave velocity of the bonded strands increases nonlinearly as the applied tensile stress level increases. To investigate the field applicability and feasibility of the approach, longitudinal impact-echo tests are conducted for two prestressed bonded tendons embedded in a nuclear reactor containment building. This reveals that the proposed approach is feasible and applicable for the unique identification of the existing prestress levels on the individual strands embedded in a real post-tensioned concrete structure.
Prestressed concrete exhibits resistance to damage induced by fire and associated elevated temperatures, often permitting reuse of structural elements following exposure to accidental fire. However, prudent determination of suitability for reuse or rehabilitation of fire-damaged prestressed concrete requires a post-fire structural evaluation, which can be greatly aided by application of nondestructive testing for quantitative assessment of residual material properties, structural strength, and serviceability. In this study, a suite of nondestructive inspection and evaluation methods including visual documentation, camber surveying, penetration resistance testing, and impact-echo are applied to fire-damaged and unaffected double-tee joists of a precast, prestressed roof system. Qualitative and quantitative measures of fire damage obtained through the nondestructive tests are presented and strong correlations, in particular between longitudinal wave speed estimates obtained in impact-echo testing and depth of probe penetration, are exhibited in the test results. Furthermore, the test results are compared with empirical models of residual compressive strength and residual elastic modulus of concrete following exposure to high temperatures. These results support recent laboratory studies suggesting that nondestructive measurements of longitudinal wave speed or pulse velocity through fire-damaged concrete may be linearly related to relative reductions in compressive strength. Results from a survey of the camber in the fire damaged joists is also presented with conceivable interpretation of the observed profiles to highlight the shortcomings of this often recommended practice and emphasize the need for more definitive nondestructive test methods.
This paper introduces a new method to estimate the loss of prestressing force for the externally prestressing tendon. The proposed method that combines of HGA and FEM is able to identify the lost tensile force of a externally prestressed tendon. The identification variables of the proposed method is a exteranlly prestressed tendon of tension, effective nominal diameter, mass per unit length and Rayleigh damping coefficients. First of all, a finite element model system is constructed to consider the effect of damping, and these variables are identified using inverse analysis technique - updating algorithm. Finally, throughout total 3 cases of numerical tests, the numerical propriety of the proposed method is verified. Here, it is seen that the errors in the estimated variables by the proposed method are about 1% except in the case of Rayleigh damping coefficients.
