Roof Diaphragm Distributed Yielding Concept for Improved Seismic Collapse Performance of Buildings With Rigid Walls and Flexible Roof Diaphragms

Abstract eng:
Buildings with rigid walls and flexible roof diaphragms (RWFD) are a common type of single-story construction in North America, Europe and New Zealand that incorporate rigid in-plane concrete or masonry walls and flexible in-plane wood or steel roof diaphragms. RWFD buildings have shown poor seismic performance during past earthquake events. In particular, it has been observed that the global seismic response is dominated by the response of the roof diaphragm, which is mainly attributed to large in-plane roof displacements that significantly exceed the displacements of in-plane walls. The present study explores the concept of distributed yielding in the flexible roof diaphragm by weakening certain intermediate diaphragm zones as a cost effective means to improve the seismic collapse capacity of RWFD buildings and mitigate their seismic vulnerability. A numerical framework was developed specifically for analyzing RWFD buildings and was used to evaluate the proposed concept. Results of nonlinear dynamic time-history response analyses conducted on a typical RWFD building incorporating a wood roof diaphragm show that distributing the inelastic response of the flexible diaphragm along its span is beneficial to the seismic collapse capacity of RWFD buildings. A seismic design approach based on this concept is also formulated and proposed for implementation into the U.S. building codes as an alternative seismic design approach for this type of structure.

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