UCLA

Based on a substantial amount of research on the seismic performance of reinforced concrete structural walls (shear walls), modern design provisions for mid-rise and high-rise shear wall buildings have been developed with the goal of achieving significant ductility in the event of strong earthquake ground shaking. Observations following recent earthquakes in Chile (2010) and New Zealand (2011) have demonstrated that shear wall buildings designed according to modern seismic design codes for tension-controlled action may be vulnerable to brittle compression failure. For walls designed to yield in compression, current reinforced concrete design standards in the United States (ACI 318-14) assume that ductility is ensured if code-prescribed confinement provisions are satisfied at wall boundaries; however, recent laboratory tests suggest that thin, code-compliant walls may be susceptible to compression failure prior to achieving the inelastic deformation capacity assumed by current U.S. design codes (i.e., ASCE 7-10, ASCE 41-13).

Seven, approximately one-half scale, ACI 318-14 compliant wall specimens (designated WP1-WP7) were subjected to reversed cyclic lateral loads and constant axial load. The specimens represented approximately the bottom 1.5 stories of an eight story cantilever wall. The first phase of testing (WP1-WP4) was conducted to identify potential deficiencies in current provisions. Test variables for the phase 1 specimens included the configuration of boundary longitudinal reinforcement, quantity and arrangement of boundary transverse reinforcement, and compression depth (influence by axial load, quantity of longitudinal reinforcement, and wall cross-section). For the second phase of testing (WP5-WP7), walls were designed either with thicker cross-sections, improved boundary transverse reinforcement details (i.e., continuous transverse reinforcement detail rather than hoop and cross-tie detail), or both. Phase 2 specimens were constructed with improved web details whereby longitudinal reinforcement was placed inside of transverse reinforcement and, in some cases, cross-ties were used to provide lateral restraint to longitudinal reinforcement.

Abrupt compression failures occurred at plastic rotations as low as 1.1% for the thinnest walls. Plastic rotations greater than 2.5% were observed for walls that were 25% and 50% thicker and/or constructed with more stringent confinement detailing than required by ACI 318-14. Based on experimental results, it is suggested to improve the deformation capacity of thin walls by avoiding the use of cross-tie confinement, and using overlapping hoops or continuous transverse reinforcement instead. Within the web region of walls, it is recommended to provide transverse reinforcement for web longitudinal reinforcement within the plastic hinge region. A lateral drift capacity prediction equation was developed in a displacement-based design format and was shown to agree with experimentally measured drift capacities for a small database of slender wall laboratory tests. It was demonstrated that, in addition to provided boundary transverse reinforcement, drift capacity of slender walls is most impacted by compression depth (c), wall thickness (b), and wall length (lw). Based on experimental data, drift capacities greater than 2% may be expected for code compliant walls designed such that c/b<2.5, while drifts lower than 1% are expected when c/b>5.0.