Design and Shake-Table Testing of a Full-Scale, Six-Story Mass Timber Building with Posttensioned Rocking Walls and Buckling-Restrained Boundary Elements

Abstract

Although dynamic contributions from higher modes are known to influence the force demands in mass timber rocking walls, higher-mode force and acceleration demands have not been formally addressed in a design procedure incorporating limit states at multiple intensity levels. This study assessed the design and dynamic response of posttensioned (PT) mass ply panel (MPP) rocking walls with buckling-restrained boundary elements (BRBs), referred to as MPP-BRB walls. A design approach using multiple modes to estimate system-level dynamic demands was adopted for the design of MPP-BRB walls and assessed via shake-table testing of a full-scale, six-story, mass timber building at the National Hazards Engineering Research Infrastructure (NHERI) Large High-Performance Outdoor Shake Table (LHPOST6) at the University of California, San Diego (UCSD). To meet global and local performance criteria at service, design, and risk-targeted maximum considered earthquake ( MCE R ) seismic intensity levels, the test specimen was designed using a modal combination rule, which assumes the higher modes superimpose with a first mode governing the nonlinear response. The modal combination rule was validated through comparison of modal estimates for peak response derived using the test specimen’s modal properties identified in white-noise testing and measured story drift, story force, and floor acceleration demands. The testing program utilized ground motion records scaled to the MCE R design spectrum for a hypothetical Seattle site, where ground motions were chosen to demonstrate the potential for higher-mode effects in the rocking system. After 18 tests with ground motion intensities ranging from 10% MCE R to 110% MCE R , the building exhibited negligible observable residual drifts. The MPP-BRB system behaved as intended, with the rocking wall enforcing a near-uniform distribution of story drift and the posttensioning enabling recentering. The design approach was able to represent the distribution and peak values of the experimentally observed responses, including posttensioning force stability, wall uplift, story drifts, floor accelerations, and force demands.