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Studies of nonstructural components in tall mass timber buildings with cross-laminated timber rocking walls
AdvisorRyan, Keri L
Civil and Environmental Engineering
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In recent years, the performance-based design methodology is helping to meet objectives for resiliency against natural hazards. Post-tensioned cross-laminated timber (CLT) rocking walls are being developed as a seismic resilient lateral load resisting system for mass timber building construction. However, achieving whole building resiliency heavily depends on the resiliency of nonstructural systems, as they comprise the majority of construction costs and are sensitive to low shaking intensities. Nonstructural components can be drift-sensitive, acceleration-sensitive, or sensitive to both drift and acceleration. The mass timber building integrated with the post-tensioned rocking wall system has some features that can affect all nonstructural components. These buildings are flexible and incur significant inter-story drift without much damage to the structural system. Moreover, a rocking wall can induce impact-related high-frequency acceleration spikes. The current study addresses these concerns by evaluating the dynamic response of mass timber buildings integrated with a post-tensioned rocking wall, proposing and investigating low-damage details of partition walls, and evaluating the structural/non-structural interaction effects of including the stiffness and strength of partition walls response in the simulation of the dynamic response of these types of buildings.Initially, a two-story mass timber building tested at the NHERI@UCSD large high-performance outdoor shake table was studied. Data from this experiment showed that although the high-frequency spikes occurred in post-tensioned CLT rocking walls, they were attenuated in the diaphragm. Moreover, it was shown that modeling assumptions such as flexible diaphragm and wall to diaphragm connection could affect the numerical simulation of accelerations in the rocking walls and floor diaphragms of the mass timber building. Subsequently, a few details aimed to reduce the seismic damage to the partition walls were developed and investigated in a series of experiments performed at the NHERI@Lehigh equipment facility. These experiments showed that bidirectional loading had an insignificant influence on the in-plane resistance of the partition walls, and the overall resistance of the partition walls was trivial compared to the entire sub-assembly. In experiment Phase 1, telescoping detailing (nested or double slip track) was shown to eliminate the damage to the framing at the wall ends compared to traditional slip-track detailing. In Phase 2, including a gap through the corner could eliminate all but cosmetic damage up to more than 2% drift, while including distributed gaps (expansion joints) throughout the wall delayed the onset of damage at the wall intersection to about 1% drift. Finally, structure/nonstructure interaction effects were evaluated in two 5 and 12 story mass-timber buildings integrated with post-tensioned cross-laminated timber rocking walls. Two-dimensional models of representative coupled rocking wall units were developed in OpenSees, and concentrated spring models representing different partition walls with different densities were integrated into these models. Different analyses were performed on the bare rocking wall structure, and the structure integrated with partition walls. Partition walls with classic fixed connection detailing were found to reduce story drift and story shear forces, which can benefit the design of the structure. Partition walls detailed to slip, however, offer little resistance and do not affect the structural response.