Seismic Design and Testing of Rocking Cross Laminated Timber Walls

Abstract

Mass timber is an attractive alternative to nonrenewable materials such as concrete and steel. High rise timber buildings have not been built in high seismic areas due to lack of ductile lateral force resisting systems that can have large seismic force reduction factors. Seismically resilient, lateral systems for tall timber buildings can be created by combining cross laminated timber (CLT) panels with post-tensioned (PT) self-centering technology. The concept features a system of stacked CLT walls where particular stories are equipped to rock against the above and below floor diaphragms through PT connections and are supplemented with mild steel U-shaped flexural plate energy dissipation devices (UFPs). Experiments were conducted to better understand rocking CLT wall behavior and seismic performance. The testing program consisted of five single wall tests with varying PT areas, initial tensioning force, CLT panel composition, and rocking surface and one coupled wall test with UFPs as the coupling devices. The walls were tested with a quasi-static reverse-cyclic load protocol. The experimental results showed a ductile response and good energy dissipation qualities. To evaluate the feasibility and performance of the rocking CLT wall system, prototype designs were developed for 8 to 14 story buildings in Seattle using a performance-based seismic design procedure. Performance was assessed using numerical simulations performed in OpenSees for ground motions representing a range of seismic hazards. The results were used to validate the performance-based seismic design procedure for tall timber buildings with rocking CLT walls.