Post-tensioned Concrete Walls Research Articles

Nonlinear static and dynamic behaviors assessment of self-centering post-tensioned concrete wall with multiple-slit device

Conventional seismic force-resisting systems usually experience significant structural damage, and repairing such buildings is not economical. A new type of seismic force-resisting system is self-centering Post-Tensioned Concrete Wall (PT-CW), in which vertical Post-Tensioned (PT) cables supply the return force of the structure to its initial state. This study is dedicated to investigate the seismic behavior of the self-centering PT-CW system using nonlinear static, cyclic, and response history analyses. The loading and design of the studied buildings are performed in the 3D model, then one of the frames is selected and the nonlinear analyses are done in OpenSees software. In order to increase the absorption energy of PT-CW, a Multi-Slit Device (MSD) is employed. For this purpose, three systems including PT-CW with Energy Dissipators (ED) bars, PT-CW with MSD, and traditional Concrete Shear Wall (CSW) are modeled in Opensees software. These seismic force-resisting systems are applied into three, six, and ten-story buildings. To validate the proposed models, the results of an experimental study are applied. Then, the nonlinear responses of the introduced models are numerically obtained as well. Accordingly, the PT-CW with MSD has more ductility and less strength drop than the other two systems. Finally, ten far-field earthquake records are selected and scaled with the ASCE spectrum to implement NRH analysis. As a result, it is observed that the story drift of the PT-CW with MSD under the applied earthquake records is almost uniform and less than the PT-CW with ED bars.

Research on seismic behavior of unbonded post-tensioned concrete wall with vertical energy-dissipating connections

An unbonded post-tensioned (PT) concrete wall system with vertical energy-dissipating connections (UPTW-VEC) is proposed that consists of precast wall panels, several X-shaped metal dampers (XMD), mild steel energy-dissipating bars (ED bars) and PT tendons. In this wall system, the precast wall panels are assembled through XMDs along the vertical joints and ED bars along the horizonal joints to provide the energy-dissipating capacity. The PT tendons installed at the wall toes are used to provide the self-centering capacity. In addition, each wall toe is protected by a steel jacket from the concrete corners spalling or crushing. Firstly, the hysteretic behavior of XMD was studied experimentally. Then, the seismic behavior of the unbonded post-tensioning concrete wall with different parameters were investigated experimentally based on four specimens. It was shown that the wall panels were resilient after tests and the cracks were only observed near the embedded plate in wall panels. In addition, a simplified analysis method was proposed, and the theoretical results matched well with the experimental results. Finally, the finite element analysis (FEA) model of UPTW-VEC was established. Following validating through the experimental results, a parametric study was conducted to investigate the influence of critical parameters on the seismic behavior of UPTW-VEC.

A Seismic Design Procedure for Different Performance Objectives for Post-Tensioned Walls

ABSTRACT A method is presented for the design of unbonded post-tensioned concrete walls for seismic loading to satisfy multiple performance objectives. It takes advantage of the fact that the initial stiffness of the wall is nearly independent of the amount of post-tensioning reinforcement, and thus the fundamental period of the building can be considered to be a stable parameter in design of walls of a given cross section, independent of the degree of post-tensioning. The design spectra used to follow the specification provided in Eurocode 8 considering the probability of exceedance of the seismic action. A detailed example is provided.

Snap back testing of unbonded post-tensioned concrete wall systems

Unbonded Post-Tensioned (UPT) precast concrete systems have been shown to provide excellent seismic resistance. In order to improve understanding of the dynamic response of UPT systems, a series of snap back tests on four UPT systems was undertaken consisting of one Single Rocking Wall (SRW) and three Precast Wall with End Columns (PreWEC) systems. The snap back tests provided both a static pushover and a nonlinear free vibration response of a system. As expected the SRW exhibited an approximate bi-linear inertia force-drift response during the free vibration decay and the PreWEC walls showed an inertia force-drift response with increased strength and energy dissipation due to the addition of steel O-connectors. All walls exhibited negligible residual drifts regardless of the number of O-connectors or the post-tensioning force. When PreWEC systems of the same strength were compared the inclusion of further energy dissipating O-connectors was found to decrease the measured peak wall acceleration. Both the local and global wall parameters measured at pseudo-static and dynamic loading rates showed similar behaviour, which demonstrates that the dynamic behaviour of UPT walls is well represented by pseudo-static tests. The SRW was found to have Equivalent Viscous Damping (EVD) between 0.9-3.8% and the three PreWEC walls were found to have maximum EVD of between 14.7-25.8%.

Shake table testing of unbonded post-tensioned concrete walls with and without additional energy dissipation

Recently an innovative unbonded Post-Tensioned (PT) concrete wall system was developed that consists of a Precast Wall with End Columns (PreWEC). Dynamic testing was conducted to better understand the seismic response of PreWEC systems and to provide further dynamic test results of PT rocking wall systems. Three unbonded PT concrete walls, including one SRW and two PreWEC systems that incorporated O-connector dissipaters were subjected to a suite of seven spectrum compatible ground motions at different intensity levels in addition to three recent ground motions at natural scale. Negligible damage to the concrete wall panels was observed for all three systems throughout the entire sequence of testing. As expected both PreWEC systems demonstrated higher energy dissipation and lateral-load capacity in comparison to the SRW due to the addition of the O-connectors. This resulted in SRW-A experiencing higher average drifts and lower accelerations than the two PreWEC systems. An intensity measure referred to as an ‘Achieved return period factor’ was defined based on comparing the measured table acceleration response spectrum to a target code response spectrum. The increased spread of both peak acceleration and peak drift versus the achieved return period factor for SRW-A in comparison to both PreWEC systems highlights the more sensitive and unpredictable nature of the SRW as a result of limited damping. The measured inherent damping from the white noise tests was found to range between 3.5% and 4.0% for the three walls. Negligible residual drifts were measured for all walls despite higher static residual drifts being estimated from previously performed cyclic testing on identical walls.

Cyclic testing of unbonded post-tensioned concrete wall systems with and without supplemental damping

A series of cyclic lateral-load tests were conducted on four different unbonded post-tensioned precast concrete wall systems, including two Single Rocking Walls (SRW) and two PREcast Wall with End Columns (PreWEC). The main purpose of these tests was to systematically investigate the cyclic response of post-tensioned concrete walls with varying amounts of supplemental damping while keeping the initial post-tensioning force, wall dimensions, and confinement details constant. A secondary objective was to validate the wall panel design including the appropriate selection of axial force ratio and design of confinement and armouring details. All of the test walls exhibited excellent performance with uplift and rocking at the wall base with only minor damage observed, consisting of small amounts of spalling in the wall toes. There were consistent observations and measurements of the wall damage, concrete compressive strains, and wall neutral axis depths for both the SRW and PreWEC systems with the same wall panel dimensions. Based on these observations it is concluded that the behaviour of the wall panel in a PreWEC system is independent of the number of energy dissipating O-connectors. The O-connectors increased the hysteretic energy dissipation in the wall system and provided between 1.1% and 1.4% of additional equivalent viscous damping per connector for the PreWEC walls tested. Overall, the behaviour of the four walls tested confirmed the design procedures used, with both the global force-displacement response and local response parameters predicted with sufficient accuracy using an existing simplified analysis method.

Force–displacement behavior of unbonded post-tensioned concrete walls

In this paper the behavior of unbonded post-tensioned concrete walls (PT-CWs) was studied. The accuracy of the existing equations provided in international concrete codes in predicting the in-plane flexural strength of unbonded PT-CWs was investigated using a database of 30 walls. Two recently developed models for unbonded wall members with varying distributions of tendons along the wall length were also considered. An analytical procedure, based on the mechanics of rocking walls and geometric compatibility conditions was employed to characterize the lateral force behavior of unbonded PT-CWs. Using the experimental results, the displacement ductility was determined for the considered walls. According to the results, although the expressions provided by the concrete design codes of the United States (ACI 318-14), New Zealand (NZS 3101) and Australia (AS 3600) to calculate the stresses in tendons of unbonded members were originally developed for beam elements, they resulted in a reasonable strength prediction of wall members. However, the concrete design code of Canada (CSA-A23.3-04) provides a highly unconservative prediction of the flexural strength of unbonded PT-CWs. The presented analytical procedure was able to effectively predict the capacity curve of the tested walls. This research also showed that at low levels of axial stress ratio the ductility of unbonded PT-CWs is highly sensitive to small changes in the level of axial stress.

Unbonded Tendon Stresses in Post-Tensioned Concrete Walls at Nominal Flexural Strength

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Design of Rectangular Openings in Precast Walls Under Vertical Loads

One of the successful precast concrete systems that has emerged from the PRESSS (PREcast Seismic Structural Systems) research program is the unbonded post-tensioned concrete wall system. This paper addresses the use of these walls with rectangular openings to accommodate architectural, mechanical, and safety requirements. The openings can cause large tensile stresses and, thus, cracking in the wall panels. Little information is available to aid in the design of the panel reinforcement around the openings to limit the size of these cracks. This paper describes an analytical investigation of the behavior and design of the walls under vertical post-tensioning and gravity loads. Critical regions in the wall panels 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.