Post-tensioned Concrete Beams Research Articles

Anchorage Zone Stress Mapping using ANSYS

Abstract: This paper presents a comprehensive analysis of stress development in the anchorage zone of prestressed posttensioned concrete beams using the finite element method with ANSYS. Focusing on both concentric and eccentric loading scenarios, the study varies the loaded area ratio (k) to investigate its effect on stress distribution. The obtained results are meticulously compared with existing literature, enhancing understanding of the behaviour of anchorage blocks within prestressed concrete members. Beyond stress assessment, the study evaluates the performance and structural integrity of the anchorage zone, providing valuable insights for design optimization and construction practices.

Degradation of structural safety levels in prototype balanced beam systems

Post-tensioned balanced beam structures are very sensitive to natural deterioration and excessive environmental attacks, which can lead to relatively rapid drops in safety levels. Since partial failure or corrosion of pre-stressing tendons can be difficult to detect, the strategy of last resort to ensure that safety levels are acceptable remains to perform a mechanical load test, with the risks that this entails. In the case of some iconic balanced beam systems, destructive investigations are further limited by the need to comply with the deontological standards valid for cultural heritage structures. The capacity and robustness of balanced beam systems can therefore be estimated by relying primarily on accurate mechanical models and sensitivity analyses against scenarios that may degrade safety. To this end, reference models can be corroborated by information from various sources, including experimental campaigns and archives. This study, in particular, focuses on the evaluation of the residual capacity offered by Morandi's prototype balanced beam scheme, to aid prognosis, and possibly support “decision-making” for possible reuse. Finally, an experimental and numerical application to the most complex post-tensioned concrete balanced beam system ever designed by Riccardo Morandi is presented, i.e. the roofing system of Pavilion V of Torino Esposizioni dating back to the late 1950 s.

Probabilistic fatigue life prediction of corroded PC beams considering spatial variability of pitting corrosion

Pitting corrosion intensifies local stress in materials, accelerating the fatigue crack initiation and propagation at the pit root. The randomly distributed corrosion pits can result in fatigue fractures in rebars and wires at non-critical sections, which further increases the fatigue failure probability of structures. However, previous studies have scarcely taken this into account. Here, we propose a novel model for fatigue life prediction of corroded post-tensioned prestressed concrete (PC) beams, considering the spatial variability of pitting corrosion. First, a Weibull distribution model of the pitting factor is developed based on the 3D laser scanning method. Then, the 3D non-Gaussian random field of the pitting factor in PC beams is generated using the inverse Nataf transformation. Next, the 3D pit-induced stress concentration is modeled using pit shape ratios. Following that, the initiation and propagation of fatigue cracks in pitting corroded wires and rebars are considered by the equivalent initial flaw size methodology. Finally, the fatigue analyses of the pitting corroded wires and rebars in all beam elements are conducted step by step until the load-bearing capacity of PC beams becomes lower than the applied load. The proposed prediction model is validated using the experimental data. The results reveal that neglecting the spatial variability of pitting corrosion overestimates the fatigue life of corroded PC beams, especially under high corrosion degrees.

Study on the Stresses Released in a Notched, Postensioned Concrete Beam

Structural prestressed concrete elements (SPCE) face uncertainties in accurately assessing the actual prestressing force. Over time, the initial prestressing force decreases due to several factors. Incorrect estimation of prestress losses can lead to design inefficiencies or structural issues. Monitoring the prestressing force can be achieved through instrumentation during casting, but existing SPCE lack such devices, necessitating indirect methods to determine prestressing force variations. This study focuses on analyzing stresses released in a notched post-tensioned concrete beam using the saw-cutting technique. Surface notches induce local decompression, allowing for strain measurements in the isolated concrete block. These measurements, considering uncertainties in initial prestress and material properties, are analyzed through backward calculations. The findings enhance understanding of saw-cutting and enable future applications to determine effective prestressing force in unmonitored SPCE. Further experimental studies are required to explore prestressing force consistency under monitored conditions. This research provides valuable insights into the potential of the saw-cutting technique as a non-destructive testing method for assessing prestressing force in unmonitored SPCE. Accurately determining the prestressing force is crucial for evaluating existing SPCE and ensuring their structural integrity. Keywords: prestressed concrete, beam, test, saw-cut, notch

Behavior of unbonded pre-stressing concrete beams with thermal insulation coating

ABSTRACT Pre-stressing concrete is commonly used in construction. One of the challenges that pre-stressing concrete (PC) faces is that fire exposure reduces the strength and serviceability of PC elements, which requires unique design considerations. The pre-stressing strands are more sensitive to high-temperature, deform larger than mild steel, and break quicker. This research investigates the thermal and structural response of totally unbonded pre-stressing T-beams subjected to increased temperatures and continuous service loads. Thermal coating was proposed to avoid damage and load carrying capacity reduction under fire loading. Seven medium-sized post-tensioned concrete beams were tested in a fire exposure (600°C for 3 h) in order to examine the effect of the following variables: presence of thermal coating, the use of different pre-stressing ratios, increasing the concrete cover, and studying the fire effect at the end anchor, which represents the weakest point at the unbonded system. The proposed insulating technique improved pre-stressing beam behavior during fire exposure by improving crack distribution and lowering strength loss. The thermally insulated beam with a high pre-stressing ratio attained 99.3% of the control specimen load carrying capacity, compared to 86% for the unprotected beam. The deflection of the thermally isolated beam was 7.8 mm, compared to 22.7 mm for the unprotected specimen after 180 min of fire exposure. The use of low pre-stressing ratio caused the insulated pre-stressing strands to rapidly deform with low increases in temperature, which caused rapid crack formation.

A new empirical model for flexural stiffness of corroded post-tensioned concrete beams

Under service loading and environmental actions, the corrosion of steel strands would reduce the cracking load and ultimate load of post-tensioned concrete (PTC) beams. It also leads to the degradation of flexural stiffness, and hence increases the deflection of beams under the same load. In order to more effectively evaluate the stiffness degradation of corroded post-tensioned concrete (CPTC) beams, an empirical model is proposed in this work for assessing the stiffness considering the effect of the corrosion of steel strands. In the proposed model, cracking stiffness and stiffness after cracking are assessed separately, and the equations of cracking moment and ultimate moment are derived. The proposed model is verified by experimental data. Results show that the proposed model can efficiently predict the stiffness changes during the whole loading process, and the deflections predicted by the proposed model are in good agreement with experimental values. The proposed model is proved to be able to efficiently predict the stiffness degradation of CPTC beams caused by corrosion of steel strands, and can reveal the dependence of flexural stiffness on the corrosion loss of steel strands and the external loads.

Investigation of anchorage plate opening on bursting force

Three-dimensional (3D) Finite Element analyses were performed to investigate transverse stresses and bursting forces at the anchorage zone in post-tensioned concrete beams. The behavior of the concrete beam was investigated through linear elastic Finite Element analyses. To validate the Numerical modeling results, an experimental study was performed on a beam and results are compared in terms of ultimate strength. The effect of duct hole and eccentricity are investigated by varying diameter and eccentric distances on the concrete beam. Furthermore, the results are validated for bursting stress and bursting force. Altogether, the equation of bursting force in IS 1343:2012 hasn’t considered the effect of duct hole and eccentricity, the results are compared with IS 1343:2012, and an equation is presented considering the effect of duct and eccentricity.

Reinforcement determination for anchorage zones of post-tensioned concrete beams

In post-tensioned concrete beams, the high concentrated compressive forces are transmitted to the concrete zones at the beam ends through the anchorage devices. As a result, they can burst and split if the concrete is not adequately reinforced. The paper determines the reinforcement in anchorage zones with axially loaded post-tensioned tendons using the linear elastic analysis method, which involves computing the state of stresses as linearly elastic, and the equilibrium-based plasticity approach method as strut-and-tie models to provide prestressing force paths as a truss structure. Some numerical models are also analyzed to clarify the present methods.

Evaluation of experimental techniques for performance estimation of post-tensioned concrete beams

Structural health monitoring (SHM) techniques have become a significant subject in structural evaluation due to the development of non-destructive methods used to monitor and assess the integrity of structures. This paper aims to investigate the effect of damage on the flexural performance indicators and dynamic characteristics of post-tensioned concrete (PC) beams, using both static and vibration tests. The beams were tested at several load levels to reproduce different load stages of a PC member: pre-cracking, during and after the formation of initial cracks, and finally, during and after the formation of larger significant cracks. The performance of the elements is evaluated based on static data, energy calculations, and the three criteria of ACI 437 recommendations. Data from the vibration tests were used to identify the changes in modal parameters after different load levels. Acoustic emission data analysis and results were used to classify the level of damage. Experimental bending stiffness and crack length determination via visual inspection was used as control parameters to assess the deterioration levels of the beams. The outcomes of this study show the relationship level among the different experimental responses obtained: flexural performances, the presence of damage in the beams, and natural frequencies. By considering the relationships of the SHM techniques and their individual findings, the evaluation of performance indicators or damage classification in rectangular concrete prestressed beams reveals that the main limitation is the required knowledge about the previous response of the system.

Comparison of Bursting Forces in Concrete Post-Tensioned Beam using Two Modeling Approaches

A case study on a rectangular post-tensioned concrete beam end block with 3-dimensional analysis is presented in this paper. ANSYS software is used to model the end-block of a post-tensioned concrete specimen i.e., beam. An actual anchorage plate, widely used in construction is modeled with two different approaches, and a concentrated jacking force is applied to the same anchorage area. A case study is performed in which two different modeling approaches are used to model the end plate. For both modeled plates, the results are obtained and findings are compared in terms of stresses, its location and bursting force. Different equations from various design manuals are used to compare the calculated bursting tensile force.

Experimental and Numerical Research of Post-Tensioned Concrete Beams.

The purpose of this paper is to present a new approach for the modelling of post-tensioned beams with calibration of the FE model to experimental results until the load capacity and post-critical state are reached. Two post-tensioned beams with different nonlinear tendon layouts were analysed. Material testing for concrete, reinforcing steel and prestressing steel was performed prior to the experimental testing of the beams. The Hypermesh program was used to define the geometry of the spatial arrangement of the finite elements of the beams. The Abaqus/Explicit solver was used for numerical analysis. The concrete damage plasticity model was used to describe the behaviour of concrete with different laws of elastic-plastic stress-strain evolution for compression and tension. Elastic-hardening plastic constitutive models were used to describe the behaviour of steel components. An effective approach to modelling the load was developed, supported by the use of Rayleigh mass damping in an explicit procedure. The presented model approach ensures good agreement between numerical and experimental results. The crack patterns obtained in concrete reflect the actual behaviour of structural elements at every loading stage. Random imperfections found during experimental studies on the results of numerical analyses were also discussed.

Experimental research on flexural behavior of post-tensioned self-compacting concrete beams with recycled coarse aggregate

Self-compacting concrete with recycled coarse aggregate (RCASCC) is a green concrete material with high performance. However, it bears the disadvantages of low elastic modulus and high brittleness compared with ordinary concretes. In this study, recycled coarse aggregate (RCA) obtained from C30 concrete block discarded in laboratory research and tests was used to produce post-tensioned self-compacting concrete (PSRC) beams, while coarse natural aggregate (NCA) was used to produce post-tensioned natural concrete (PNC) beams. The four-point bending tests were carried out on PSRC and PNC beams to analyze the variations between the flexural performance of PSRC and PNC beams. In addition, we discuss the applicability of the current design codes on PSRC beams. The results reveal that the failure mode of PSRC beams is similar to that of PNC beams, whereas it differs significantly in the number and scope of cracks. Moreover, the variations can be reduced by increasing the ratio of non-prestressed reinforcement. In general, the PSRC beam is more ductile than the PNC beam. The increase in the ratio of non-prestressed reinforcement reduced the ductility of the PSRC beam as well as the fluctuations in the ductility of PSRC and PNC beams. Compared with the PNC beam under the same conditions, the PSRC beam exhibited a similar flexural capacity, the cracking load and maximum crack width decreased significantly, and its working deflection increased slightly. According to the calculation and analysis, ACI318-08 can be applied for calculating the cracking load, flexural capacity, and working deflection of the PSRC beams, but not the maximum crack width; GB50010-2010 is applicable for calculating the cracking bending moment and flexural capacity of PSRC beams, but the calculation deviation of the working deflection and maximum crack width is large; EN1992-1-1:2004 is applicable for calculating the crack bending moment of PSRC beams, but it is not safe for evaluating the bending capacity, working deflection, or maximum crack width. Overall, the average crack spacing correction formula proposed through experimental tests in this study can be applied to determine the maximum crack width of PSRC beams, and its accuracy is higher than that of the above-stated specifications.

Experimental investigations of flexural and shear behavior of continuous prestressed HSC beams under repeated loads

The results of an experimental study into the flexural and shear conduct of continuous two span unbonded posttensioned high strength concrete beams subjected to static and a limited number of repeated loading cycles are presented in this paper. The experimental program comprising testing and experimentation of four continuous unbonded posttensioned high strength beams with a total length (4300) mm. The main objective of this study was to see how the strength and serviceability of continuous prestressed concrete beams were affected by restricted repeated loading cycles. As a result, these beams were split into two similar groups. The first set consisted of two beams to study the flexural behavior. The second set consisted of two beams to study the shear behavior. For each set one tested under static loads and the second tested under repeated loads. They were subjected to two concentrated loads in the middle of each span loads up to destruction. It was determined that the repeated load ranged between 0.4 and 0.6 of the ultimate load generated by the static test. Immediately following the ten cycles, the load was withdrawn, and the beams were subjected to a monotonic static test until failure was achieved. Recorded the cracking and ultimate load capacity, midspan deflections, and crack widths. The experimental results explained that the ultimate flexural and shear strength for beams that are tested under repeated loads is a little reduced (1.7%) and (3.9%) comparing with the strength of the identical beams under monotonic static loading and increasing the ultimate deflection after ten cycles of repeated loading, decreased about (5.3%) and (15.1%) for flexural set and shear set, respectively.

AE localization issues in heavy reinforced post-tensioned concrete beams

Damage localization is a relevant issue in structural health monitoring (SHM) of concrete structures. A greater level of insight into the structure can be so reached enabling more informed maintenance decisions and reducing operation and maintenance costs. The basic approach to acoustic emission localization, which is often referred to as the Time of Arrival (TOA) method, is based on detecting an AE source at a number of spatially-distributed sensors. However, in anisotropic media such as reinforced concrete, the basic assumptions for the TOA method become largely invalid. Different robust methods suitable to anisotropic media, incorporating an angular-dependent velocity term into the minimization process have been developed in the past. However, the wave-velocity profile is not always known. More recently a number of other authors have adopted various Bayesian approaches as part of AE localization strategies, including the use of a Markov chain Monte Carlo inference scheme as well as nonlinear Kalman filters. The use of a probabilistic approach in source location has become increasingly applied for AE source localization in complex large structures. In heavy reinforced post-tensioned concrete structures acoustic wave path can be significantly influenced by rebars as well as metallic post-tensioning ducts. Cracks opening can further influence acoustic propagation paths and greatly influence the reliability of AE source localization algorithms. In the present paper, different localization procedures have been developed and tested on post-tensioned concrete beams during loading and unloading cycles as well as on small homogeneous concrete blocks. In a highly emissive environment, significant difficulties have been reported also in event identification thus further reducing localization procedure reliability. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

Filtering approaches of AE data in damage severity assessment of highly emissive concrete structures under loading

The application of the AE technique in the field of civil engineering requires overcoming various issues related to several factors such as structure complexity, material nonhomogeneity, signal attenuation, environmental noise. In this concern, multivariate statistical analysis was successfully applied to manage AE data and discriminate relevant features related to main damage mechanisms in concrete. Principal component analysis (PCA) and artificial neural networks (ANN) were applied with promising results. However, a fundamental limitation of these numerical methods is that they are not user-friendly and their application requires suitable scientific expertise. In such a context, the development of an easy de-noising protocol, able to simplify the AE data analysis for damage structure assessment and failure prediction, is a fundamental improvement toward the applicability of this technology on real-scale concrete structures. In the present paper, the analysis of AE data collected during loading and unloading cycles up to the failure on a real scale post-tensioned concrete beam is reported. Different denoising approaches were adopted to remove a large incoherent AE population originating from the friction of hydraulic actuator steel plate on concrete surface and friction on beam supports during loading/unloading steps. Filtered data were then synchronized with the beam deformation and crack width opening. De-noising algorithms have then been validated by structure damage severity assessment using statistical indexes such as calm ratio, load ratio, severity, and historical index. The procedure was tested with interesting results on PT concrete beams characterized by different pre-existing damages on steel tendons. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

Investigation of Bursting Force In I-Section Post-Tensioned Anchorage Zone

In post tensioned concrete beam the high transverse tensile stress is generated and if proper reinforcement is not given, bursting may occur. To study the effect of these stresses and to find bursting stress in end region the analytical study was carried out. In present work the end block of post-tensioned prestressed concrete beam is modelled in finite element based software with eccentric tendons. The bursting zone of beam is evaluated and parametric study was carried out by varying eccentricity, anchorage ratio and web thickness of girder. The 3D modelling was done and results are compared in terms of bursting force. The results are compared with Indian Standard 1343:2012 and inferences are drawn towards the usability of IS code equation of bursting force for I-section.

New trends in assessing the prestress loss in post-tensioned concrete bridges

The evaluation of the current prestress force represents often a challenging issue during the assessment of existing post-tensioned concrete (PTC) members. In this contribution, two case studies are presented to show the efficiency of some experimental methods applied both to laboratory beams and to an in-service PTC bridge. First, the outcomes of an experimental campaign carried out on three PTC beams with a straight post-tensioned, non-grouted tendon are discussed. For each beam, three-point bending tests (3PBTs) were carried out applying increasing load steps until failure and varying the prestress force; at each load step, non-destructive tests (NDTs) were performed, namely, dynamic free vibration and ultrasonic tests. The variation of non-destructive parameters was evaluated as a function of the prestress force and of the structural damage. The second case study deals with a 50-year-old PTC bridge with grouted ducts. In this case, other than evaluating the existing geometry, structural details, and material properties, the following NDTs were performed: endoscopies, tests based on stress release, i.e., both saw-cut and wire-cut tests, and lastly, X-ray diffractometries (XRDs). The results indicate the high potential of this latter technique, which resulted more reliable and less invasive than the previous ones.

Flexural behavior of Corrosion-Damaged prestressed concrete beams

This paper presents an experimental study and theoretical analysis on corroded prestressing tendons and corroded prestressed concrete beams. 68 steel strands and steel wires were artificially corroded and monotonically tested under tensile loads. Results indicated significant degradation in both deformability and strength of the corroded tendons. A bilinear model was consequently developed to characterize the constitutive relationship of the corroded prestressing tendons. Afterward, six post-tensioned prestressed concrete beams were electrochemically corroded and flexurally tested using a four-point bending set-up. Different variables were considered, including the corrosion degree, yield strength ratio and corrosion of non-prestressed rebars. It was found that, corrosion of prestressing tendons led to a deteriorated flexural bearing capacity of a beam. The cracking load, yield load, and ultimate load all decreased with the corrosion degree. Thereafter, a theoretical approach based on the stress–strain model of corroded steel tendons was proposed to predict of flexural behavior of corroded prestressed concrete beams. Good agreement with experimental results of current study and from literature was observed.

Effect of prestressing corrosion on failure in bridges

AbstractInfrastructures (viaducts, bridges, tunnels, railways, and roads) are fundamental to allow people and goods move around a country. In particular, in Italy, due to its orographic and morphological complexity, the ratio between the number of viaducts and the national geographical extension is the largest in Europe. This kind of structure constitutes a weakness of the road networks, especially those over 50 years old, and among these, prestressed concrete structures are the most vulnerable. Therefore, the study of the robustness of an infrastructure network is a quite useful topic for modern societies and public mobility managers. The aim of the present work is to develop a reliable and fast analysis tool capable of processing many structures in a relatively short time. In order to calibrate the most suitable instrument, starting from the study of an experimental campaign on six prototypes of artificially corroded posttensioned concrete beams, the reliability of concentrated plasticity models was investigated to reproduce force‐displacement diagrams and in particular, the effect of corrosion on the moment‐curvature relationship. In fact, this method could provide a well‐defined nonlinear analysis of prestressed elements, especially in the case of grillage decks where external girders could be more affected by corrosion damage in opposition to internal girders or diaphragms. A numerical model by FEM analysis is also presented to reproduce a vulnerability study on an actual structure.

Effect of Transverse Reinforcement on Shear Response of Fiber-Reinforced Polymer Post-Tensioned Concrete Beams

Effect of Transverse Reinforcement on Shear Response of Fiber-Reinforced Polymer Post-Tensioned Concrete Beams