Post-Tensioned Precast Concrete Walls Research Articles

Experimental behavior and seismic performance assessment of Unbonded Post-tensioned Precast Concrete Walls for low-rise buildings

The current growth of the urban population has led to an increment in the housing demand, increasing the seismic exposure, especially in developing countries that struggle to provide efficient and safe housing solutions. To address this issue, it is necessary to develop structural systems that provide sufficient seismic performance while allowing reduced building time and cost. This paper presents the structural identification and seismic performance assessment of a structural system based on unbonded post-tensioned precast concrete walls. These structural walls are composed of precast concrete panels connected through shear connectors and post-tensioned using unbonded steel bars. Three unbonded post-tensioned precast concrete wall specimens were subjected to a cyclic loading test, obtaining several structural parameters from the analysis of the experimental campaign results. In addition, the seismic response of the proposed system was identified by characterizing its hysteretic behavior and by defining several experimental damage limit states. Based on these results, a numerical model was calibrated using the Pinching4 material of the OpenSees software. Finally, a numerical seismic performance assessment of the in-plane response was carried out by proposing an archetype building and using the FEMA P695 far-field ground motion set as seismic input. These analyses allowed the development of fragility functions of the diverse damage states observed on the tested specimens. The results show that the proposed structural system based on unbonded post-tensioned precast concrete walls is a feasible option for its implementation as a lateral load structural system on low-rise buildings, providing sufficient seismic capacity and allowing further improvements in its implementation.

Evaluation of the Seismic Performance of Unbonded Post-Tensioned Precast Concrete Walls with Internal and External Dampers. I: Experimental Research

Evaluation of the Seismic Performance of Unbonded Post-Tensioned Precast Concrete Walls with Internal and External Dampers. I: Experimental Research

Evaluation of the Seismic Performance of Unbonded Post-Tensioned Precast Concrete Walls with Internal and External Dampers. II: Design Criteria and Numerical Research

Evaluation of the Seismic Performance of Unbonded Post-Tensioned Precast Concrete Walls with Internal and External Dampers. II: Design Criteria and Numerical Research

Unbonded Post-tensioned Precast Concrete Walls With Rocking Connections: Modeling Approaches and Impact Damping

Over the past two decades, precast concrete members have been utilized in seismically resilient structures. In developing these structures, different techniques have been used for connecting the precast members to the foundation. In building construction, unbonded post-tensioning (PT) tendons can anchor a precast wall to the foundation, resulting in the so-called rocking wall system. The rocking wall system develops a dry connection with the foundation and provides moment resistance by means of the PT tendons. The PT tendons remain elastic when the wall is subjected to design-level ground motions to preserve the re-centering capability of the wall. Moreover, the structural damage is concentrated near the wall toes and can be minimized with proper detailing of the toes. Rocking wall systems can consist of a Single precast Rocking Wall (SRW), which uses no supplemental damping, or walls with supplemental damping in the form of viscous or hysteretic energy dissipating devices. In addition to the supplemental damping, rocking walls dissipate the seismic energy through their impacts on the foundation base, their inherent viscous damping, and the hysteresis of concrete near the wall base. While the investigation of rocking walls continues to gain interest, there is no widely accepted means of modeling their dynamic behavior. This paper investigates two popular approaches for modeling rocking walls with and without supplemental damping: the finite element method and analytical modeling. The ability of the two approaches to capture the local and global responses of the walls is evaluated against shake table tests of walls with multiple-level intensity base motions. Next, the behavior characteristics of the two modeling approaches and their ability to simulate impact damping are discussed.

Deformation and cyclic buckling capacity of external replaceable hysteretic dampers for unbonded post-tensioned precast concrete walls

This paper proposes and validates a type of external replaceable hysteretic dampers to be mainly applied to unbonded post-tensioned (UPT) precast walls. The main aim of the proposed damper was to provide the UPT walls with large energy dissipation without significant buckling. To evaluate the efficiency of these dampers, a cyclic test was conducted. The damper specimens consisted of a mild steel round bar with a reduced diameter over a fused length and an additional threaded length at each side, for installation purposes. Moreover, a round steel tube was installed over the fused length and filled with grout to delay the buckling. The proposed dampers, with different geometries and conditions, were subjected to cyclic loads to evaluate their deformation capacity and fracture mechanism. The specimens displayed a regular and stable hysteretic curve until strains of 9%, after which a flexural buckling was observed at the ends of the fused length. However, this flexural buckling did not affect the energy-dissipating capacity in any specimen. Consequently, this type of damper is considered suitable for applications in self-centering rocking walls. Furthermore, the proposed dampers fractured by a combination of low-cycle fatigue and excessive rotations at the transition length. In addition to the experimental validation, an extensive numerical investigation was conducted on the proposed damper to complement the experimental data and to provide analytical tools for design.

Effects of unbonded steel layout on seismic behavior of post-tensioned precast concrete shear walls

Unbonded post-tensioned precast connections have been studied widely in various applications and shown to be promising seismic resisting systems with superior seismic performance including exceptional self-centering capability and minimized structural damage. In this paper, effects of unbonded post-tensioned steel layout of precast concrete shear walls on seismic performance of a typical five-story precast concrete parking garage structure with the walls being the only lateral load resisting system is studied. The seismic behavior of the walls is determined using static nonlinear push-over, cyclic, and nonlinear time-history dynamic analyses under both the design and survival level ground motions. Three prototype unbonded post-tensioned precast concrete shear walls are designed with different unbonded post-tensioning steel tendon layout. Roof drift, post-tensioning force, and base shear and normal forces at the wall-foundation horizontal joint are monitored, and the demand for the coefficient of shear friction along the horizontal joint is calculated. The results show that seismic behavior of unbonded post-tensioned precast shear walls, in particular, maximum building drift, permanent losses in post-tensioning steel force, and coefficient of shear friction, is significantly influenced by layout of unbonded post-tensioned steel. The results and findings presented are valuable to improve design guidelines and provide a useful reference for practical applications of unbonded post-tensioned precast concrete connections in seismic applications.

Verification of a Simple Model for the Lateral-Load Analysis and Design of Unbonded Post-Tensioned Precast Concrete Walls

Verification of a Simple Model for the Lateral-Load Analysis and Design of Unbonded Post-Tensioned Precast Concrete Walls

Computational modelling of a four storey post-tensioned concrete building subjected to shake table testing

Prior research into low-damage wall systems has predominately focused on the walls behaviour in isolation from other building components. Although the response of these isolated walls has been shown to perform well when subjected to both cyclic and dynamic loading, uncertainty exists when considering the effect of interactions between walls and other structural and non-structural components on the seismic response and performance of entire buildings. To help address this uncertainty a computational model was developed to simulate the response of a full-scale four-storey building with post-tensioned precast concrete walls that was subjected to tri-axial earthquake demands on the E-Defence shake table. The model accurately captured the buildings measured response by incorporating the in-plane and out-of-plane non-linear behaviour of both the wall and floor elements. The model was able to simulate the deformation demands imposed on the floor due to compatibility with the post-tensioned walls, closely matching the behaviour and damage observed during the test. Dynamic loading and wall-to-floor interaction were shown to significantly increase the over-strength actions that developed when compared to the wall system considered in isolation.

Optimum seismic design of unbonded post-tensioned precast concrete walls using ANN

Precast Seismic Structural Systems (PRESSS) provided an iterative procedure for obtaining optimum design of unbonded post-tensioned coupled precast concrete wall systems. Although PRESSS procedure is effective, however, it is lengthy and laborious. The purpose of this research is to employ Artificial Neural Network (ANN) to predict the optimum design parameters for such wall systems while avoiding the demanding iterative process. The developed ANN model is very accurate in predicting the nondimensional optimum design parameters related to post-tensioning reinforcement area, yield force of shear connectors and ratio of moment resisted by shear connectors to the design moment. The Mean Absolute Percent Error (MAPE) for the test data for these design parameters is around %1 and the correlation coefficient is almost equal to 1.0. The developed ANN model is then used to study the effect of different design parameters on wall behavior. It is observed that the design moment and the concrete strength have the most influence on the wall behavior as compared to other parameters. Several design examples were presented to demonstrate the accuracy and effectiveness of the ANN model.

Experimental Lateral Load Response of Unbonded Post-Tensioned Precast Concrete Walls

Experimental Lateral Load Response of Unbonded Post-Tensioned Precast Concrete Walls

Self-Centering Behavior of Unbonded, Post-Tensioned Precast Concrete Shear Walls

Self-centering ability of unbonded post-tensioned precast concrete shear walls has been attributed to the presence of post-tensioning force. However, the experimental results presented in this paper indicate that the post-tensioning force may completely die out during cyclic loading while the walls are able to retain their superior self-centering characteristic. Moreover, the analytical study presented in this article indicates that with proper configuration of end-anchorages for post-tensioned tendons, self-centering of post-tensioned walls can be achieved even when the post-tensioning force vanishes. This study also investigates the effects of tendon layout, tendon end-anchorage configuration, and external vertical load on the self-centering ability of unbonded precast concrete shear walls subjected to earthquake loading.

Analytical and Experimental Lateral Load Behavior of Unbonded Posttensioned Precast Concrete Walls

The use of unbonded posttensioned (UPT) precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies. This paper introduces a design-oriented analytical model that uses simple formulae to estimate the nonlinear lateral load behavior of UPT walls, and compares this simple model with available experimental results. A previously developed UPT wall model based on fiber elements is also compared with experimental results. Each model is formulated to consider several critical limit states in the lateral load behavior of UPT walls. Comparisons showed generally good agreement between analytical and experimental results for three different test walls under monotonic and cyclic loading. The simple model is found to be sufficiently accurate for seismic design of UPT walls, and the fiber model is found to be sufficiently accurate for estimating UPT wall response under earthquake loading.

Seismic Design of Partially Post-Tensioned Precast Concrete Walls

This paper proposes a seismic design approach for precast concrete structural walls that use a combination of mild steel and high strength post-tensioning steel reinforcement across horizontal joints for flexural resistance. The mild steel reinforcement is designed to yield in tension and compression, providing inelastic energy dissipation. The post-tensioning steel provides self-centering capability, reducing the residual (i.e., permanent) lateral displacements of the wall due to a large earthquake. The proposed design approach is a performance-based approach that aims to limit the wall lateral displacements to an allowable target displacement. The design approach is critically evaluated based on nonlinear static and nonlinear dynamic time history analyses of two prototype walls. A design example is provided at the end of the paper.

Lateral Load Behavior of Unbonded Post-Tensioned Precast Concrete Walls with Vertical Joints

The paper describes a fiber based analytical model of unbonded post-tensioned precast concrete walls with vertical joint connectors. The model is used in an analytical study of the influence of selected wall design parameters on the lateral load behavior of a prototype wall. The paper verifies the accuracy of a trilinear idealized lateral load behavior based on the derived closed form expressions based on the results of the analytical parameter study. Recommendations based on the trends observed in the parameter study are provided to help the designers satisfy the criteria of the proposed design approach.

Seismic Design of Unbonded Post-Tensioned Precast Concrete Walls with Vertical Joint Connectors

An investigation of seismic design of precast concrete wall panels that have been connected along vertical joints with ductile connectors is presented. The panels are also connected to the foundations along horizontal joints by using unbonded post-tensioning steel. The objectives of this study are (1) to derive closed-form expressions for the base shear roof displacement capacities of unbonded post tensioned precast concrete walls and (2) to propose a design approach that relates wall capacities to code-specified design demands. Study results will also apply to walls with different numbers of panels and different panel sizes.

Hybrid Post-Tensioned Precast Concrete Walls for Use in Seismic Regions

Recent research has shown that post-tensioned precast concrete lateral load resisting walls that do not emulate the behavior of monolithic cast-in-place reinforced concrete walls have desirable seismic characteristics such as a self-centering capability and an ability to undergo nonlinear lateral displacements with little damage. The biggest disadvantage of these walls under earthquake loading is an increase in the lateral displacements as a result of small energy dissipation. This paper investigates a hybrid precast wall system that uses mild steel reinforcement in addition to the post-tensioning steel for flexural strength and inelastic energy dissipation. An analytical parametric study is conducted to compare the expected seismic behavior of a series of prototype walls with different amounts of mild steel and post-tensioning steel. Nonlinear dynamic time history analyses of the walls indicate that the use of mild steel reinforcement results in a considerable reduction in the lateral displacements of the walls under earthquake loading, particularly for walls in regions of high seismicity and with shorter periods of vibration. The results of these analyses are used to present preliminary design implications for the use of hybrid post-tensioned precast walls in seismic regions.

Design of Rectangular Openings in Precast Walls Under Combined Vertical and Lateral Loads

Recent research conducted as a part of the PRESSS (PREcast Seismic Structural Systems) research program has shown that unbonded post-tensioned precast concrete walls can be used as primary lateral load resisting systems in seismic regions. This paper investigates the design of rectangular openings in these walls under combined vertical loads due to gravity and post-tensioning, and lateral loads due to earthquakes. The openings can cause large tensile stresses and, thus, cracking in the wall panels. Under lateral loads, cracking can also occur as a result of the gaps that form along the horizontal joints between the wall panels and between the wall and the foundation. Little information is available to aid in the design of the panel reinforcement to limit the size of these cracks. In this paper, critical panel regions where bonded mild steel reinforcement is needed are identified, and a design approach is proposed to determine the required panel reinforcement. The effects of opening length, opening height, wall length, and initial stress in the concrete due to post-tensioning and gravity loads are considered. An example is included to demonstrate the proposed design approach.

Simplified Seismic Design Approach for Friction-Damped Unbonded Post-Tensioned Precast Concrete Walls

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Seismic Design of Unbonded Post-Tensioned Precast Concrete Walls with Supplemental Viscous Damping

Seismic Design of Unbonded Post-Tensioned Precast Concrete Walls with Supplemental Viscous Damping

Seismic Behavior and Design of Unbonded Post-Tensioned Precast Concrete Frames

Unbonded post-tensioned precast concrete walls are constructed by post-tensioning precast wall panels across horizontal joints using post-tensioning steel which is not bonded to the concrete. This paper describes an analytical investigation of the seismic behavior and design of these walls. Unbonded post-tensioned precast walls with strength and initial stiffness similar to monolithic cast-in-place concrete walls can be designed to soften and undergo large nonlinear lateral drift with little damage. The nonlinear behavior is primarily due to the opening of gaps along the horizontal joints. A performance-based seismic design approach is proposed in which the walls are required to resist design level ground motions with little damage and severe survival level ground motions with damage but without failure. Shear slip along the horizontal joints is prevented by design. Nonlinear dynamic analyses show that, compared to cast-in-place walls, unbonded post-tensioned precast walls undergo larger drift, but accumulate significantly smaller residual drift during an earthquake.