UCLA

Current US building codes require the Lateral-Force Resisting System (LFRS) of reinforced concrete structures resisting wind loads to be designed for elastic response. Imposing the requirement of elastic behavior may produce an overly conservative design if the lateral system has some inherent ductility and may also have unintended adverse effects on structural performance under seismic loading. Performance-Based Wind Design (PBWD), which would allow limited nonlinear behavior in key components, has been introduced by the American Society of Civil Engineers (ASCE) Structural Engineering Institute (SEI) and the American Concrete Institute (ACI) to address these issues. A critical aspect of PBWD involves an assessment of the strength and detailing requirements needed to allow limited nonlinear demands in critical components. Of particular interest is the behavior at critical sections subjected to high-cycle fatigue loading, which is common for wind loading. If detailing commonly used for special seismic systems is used, then it is reasonable to assume that behavior under high-cycle fatigue loading will be acceptable, although the importance of stiffness degradation under wind loading requires investigation. The need for improved detailing for nonlinear responses under wind loading, in addition to that required of ordinary or intermediate structural systems, requires additional study.This thesis focuses on the behavior of lap splices at critical sections in ordinary structural walls under wind loading. A detailed literature review was conducted and it was revealed that the existing information in the literature is insufficient to develop recommendations; therefore, an experimental program was developed. Lap splice behavior was initially investigated by testing T-beams subjected to 4-point loading, which are cheaper to construct and easier to test than walls, followed by testing of C-shaped walls. The T-beam tests were conducted in two phases: Phase I involved three smaller scale beams with #4 Grade 80 longitudinal reinforcement to provide the information needed to develop the wall test program; Phase II was conducted on two larger T-beams with #8 Grade 80 longitudinal reinforcement to address potential issues associated with the use of larger bar sizes. The beams were designed to reproduce the strain demands expected in the test wall longitudinal reinforcement under a prescribed wind-loading protocol. Two main variables were considered to evaluate the lap splice behavior: lap splice length and transverse reinforcement spacing in the splice region. The longitudinal bars were spliced according to ACI 318-19 provisions. For the initial small beam tests, splice failure was observed prior to reaching bar yield; therefore, in subsequent tests, a multiplier of 1.25 was used to account for strain hardening behavior of the longitudinal reinforcement; this approach is consistent with provisions for special walls (ACI 318-19 Chapter 18.10.2.3). The small beam tests, with tie spacings of 2, 3, and 6 in., revealed that tight spacing (2 in.) was required to resist the entire wind loading protocol without strength loss. To enable comparisons between the small and large beam tests, a parameter asp, which is the ratio of the total confining force provided by the transverse reinforcements along the splice length to the total yield strength of the spliced bars, was used. The performance of the small and large beams with comparable asp factors was similar, indicating no bar size effect between #4 and #8 spliced longitudinal reinforcement. For the given loading protocol, minimum asp values of 1.25 and 2.0 are recommended for lap splices if strain ductility demands are ≤ 6 or ≥ 10, respectively.