Precast concrete shear walls with unbonded post-tensioning, which resist seismic loads have attracted the attention of researchers over the past 20 years. This study provides a database of a special subset of precast concrete shear walls tested under monotonic or cyclic loading: rocking walls, hybrid walls, and walls with end columns.
These shear walls experience joint opening, undergo rocking motion over the foundation, and utilize unbonded post-tensioning to self-center after load removal. Seismic energy is dissipated in distinct ways that vary from nonlinearity of concrete and post-tensioning strands (rocking walls) to yielding of mild steel reinforcement or external energy dissipaters (hybrid walls and walls with end columns).
The experimental drift capacity, strength, and damage sequence of walls from the literature were compiled. Onsets of cover concrete spalling, yielding of energy dissipaters, yielding of post-tensioning strands, fracture of energy dissipaters, and crushing of confined concrete were reported. ACI guidance on shear walls were evaluated by comparing the lateral drift and strength measured by testing and predicted by ACI.
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A study on Residual Drift and Concrete Strains in Unbonded Post-Tensioned Precast Rocking Walls
Modern seismic resistant design has been focusing on development of cost effective structural systems which experience
minimal damage during an earthquake. Unbonded post-tensioned precast concrete walls provide a suitable solution due to their
self-centering behavior and their ability to undergo large nonlinear deformation with minimal damage. Several experimental
and analytical investigation focusing on lateral load resisting behavior of unbonded post-tensioned precast walls has been
carried out in the past two decades. These investigations have primarily focused on lateral load resistance, self-centering
capacity, energy dissipation and extent of damage in confined concrete region of the wall system. Past experimental results
have shown that self-centering capacity of the wall system decreases at higher lateral drifts. Particularly, rocking walls with
higher energy dissipation capacity, sustain considerable residual displacement. This residual displacement in the wall system
may affect the ability of the entire structure to re-center. Though increasing initial prestressing force helps in reducing residual
drift, it also subjects concrete to increased axial compressive stress which may lead to premature strength degradation of
confined concrete in rocking corners. Accurate prediction of expected concrete strains in confined regions during increasing
drift cycle is critical in design of such wall systems. Simplified design procedures available in literature assume different values
for plastic hinge length to estimate critical concrete strain values. The results from the experimental tests available in literature
were analyzed, to understand the effects of energy dissipating elements on residual drift and to examine the accuracy of
simplified design procedures in predicting critical concrete strain. Based on the findings, recommendations are made on design
of energy dissipating elements and plastic hinge length for unbonded post-tensioned precast rocking walls.
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- Award ID(s):
- 1662963
- NSF-PAR ID:
- 10107164
- Date Published:
- Journal Name:
- Proceedings of the ... Canadian Conference on Earthquake Engineering
- ISSN:
- 0228-8133
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Precast concrete shear walls with unbonded post-tensioning, which resist seismic loads have attracted the attention of researchers over the past 20 years. This study provides a database of a special subset of precast concrete shear walls tested under monotonic or cyclic loading: rocking walls, hybrid walls, and walls with end columns. These shear walls experience joint opening, undergo rocking motion over the foundation, and utilize unbonded post-tensioning to self-center after load removal. Seismic energy is dissipated in distinct ways that vary from nonlinearity of concrete and post-tensioning strands (rocking walls) to yielding of mild steel reinforcement or external energy dissipaters (hybrid walls and walls with end columns). The experimental drift capacity, strength, and damage sequence of walls from the literature were compiled. Onsets of cover concrete spalling, yielding of energy dissipaters, yielding of post-tensioning strands, fracture of energy dissipaters, and crushing of confined concrete were reported. ACI guidance on shear walls were evaluated by comparing the lateral drift and strength measured by testing and predicted by ACI.more » « less
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Abstract Hybrid sliding‐rocking (HSR) bridge columns are precast concrete segmental columns with unbonded posttensioning, end rocking joints, and intermediate sliding joints. Having been developed for construction in seismic regions, HSR columns offer self‐centering, energy dissipation, and low damageability. Recent advances in the computational modeling of HSR columns have resulted in the proposal of a number of refinements to their original design, leading to the introduction of
Second‐Generation HSR columns. Compared to First‐Generation HSR columns, Second‐Generation HSR columns use a reduced number of sliding joints made of high‐performance polytetrafluoroethylene (PTFE) materials to provide desirable levels of sliding and frictional energy dissipation. The seismic performance of Second‐Generation HSR columns was recently investigated through an extensive experimental study. The present paper discusses the major results of the tests performed on two half‐scale HSR column specimens under combined lateral‐torsional loading and biaxial lateral loading to demonstrate their performance under such loading scenarios. A variety of loading protocols were used to test each column specimen, including both cyclic and arbitrary paths. Both columns sustained minimal damage under displacement demands representing 975‐ and 2475‐year seismic hazards, meeting their design objectives. Because of the torsional sliding at sliding joints, the column subjected to lateral‐torsional loading did not exhibit any distinct torsional damage. The biaxial lateral loading was, however, found more damaging to HSR columns than torsional and uniaxial lateral loading. -
null (Ed.)Nonlinear time history analyses were conducted for 5-story and 12-story prototype buildings that used post-tensioned cross-laminated timber rocking walls coupled with U-shaped flexural plates (UFPs) as the lateral force resisting system. The building models were subjected to 22 far-field and 28 near-fault ground motions, with and without directivity effects, scaled to the design earthquake and maximum considered earthquake for Seattle, with ASCE Site Class D. The buildings were designed to performance objectives that limited structural damage to crushing at the wall toes and nonlinear deformation in the UFPs, while ensuring code-based interstory drift requirements were satisfied and the post-tensioned rods remained linear. The walls of the 12-story building had a second rocking joint at midheight to reduce flexural demands in the lower stories and interstory drift in the upper stories. The interstory drift, in-plane wall shear and overturning moment, UFP deformation, and extent of wall toe crushing is summarized for each building. Near-fault ground motions with directivity effects resulted in the largest demands for the 5-story building, while the midheight rocking joint diminished the influence of ground motion directivity effects in the 12-story building. Results for both buildings confirmed that UFPs located higher from the base of the walls dissipated more energy compared to UFPs closer to the base.more » « less
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Driven by demand for sustainable buildings and a reduction in construction time, mass timber buildings, specifically cross-laminated timber (CLT), is being more widely used in mid-rise buildings in the US. Low damage post-tensioned self-centering (SC) CLT shear walls (SC-CLT walls) provide an opportunity to develop seismically resilient CLT buildings. Previous research focused primarily on the lateral-load response under unidirectional loading of isolated self-centering timber walls, without considering the interaction with the adjacent building structural components, i.e., the floor diaphragms, collector beams, and gravity load system. Buildings response under seismic loading is multidirectional and there are concerns that multidirectional loading may be more damaging to SC-CLT wall panels and the adjacent building structural components than unidirectional loading, which affects the potential seismic resilience of buildings with SC-CLT walls. A series of lateral-load tests of a 0.625-scale timber sub-assembly was conducted at the NHERI Lehigh Large-Scale Multi-Directional Hybrid Simulation Experimental Facility to investigate the the lateral-load response and damage of SC-CLT walls and the capability of the adjacent building structural components i.e., the floor diaphragms, collector beams, and gravity load system to accommodate the building response and the controlled-rocking of the SC-CLT walls under multidirectional lateral loading.more » « less
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