Evaluating Existing and Proposing New Seismic Design Provisions for Rigid Wall - Flexible Diaphragm Buildings
Published in 83rd SEAOC Annual Convention Proceedings: Indian Well, CA, September 10, 2014, pages 116-129.
Buildings with heavy concrete on masonry walls supported by flexible wood or steel deck roof diaphragms are ubiquitour across the United States and the rest of North America. The current seismic design approach is based on the equivalent lateral force (ELF) method whose underlying assumptions significantly differ from the actual dynamic response of these buildings. The seismic behavior of rigid wall-flexible rood diaphragm (RWFD) Buildings is dominated by the diaphragm's response instead of the wall' in-plane response. Furthermore, the diaphragm's ductility and overstrength capacity is unique to its own construction. Yet the current design methodology employed by practitioners directly ties the diaphragm shears and overstrength to the characteristics of the seismic force0resisting system's (SFRS) vertical elements.
Past problems in these buildings have been the repeated failures of the walls' anchorage to the diaphragm, and through a series of "trial and error" iterations, the current design provisions have evolved. current wall anchorage forces for RWFD buildings are believed to now be near maximum expected force levels with litter necessary reliance on connector ductility; however, solving the wall anchorage issue may result in new failures within the diaphragm itself.
Using a dedicated numerical modeling framework coupled with a FEMA P-695 collapse capacity evaluation process, a research study was conducted t evaluate performance for a variety of RWFD archetypes conforming to ASCE/SEI 7-10, as well as redesigned archetypes conforming to a new design methodology. Furthermore, a review of the predicted wall anchorage forces in FWFD buildings was also compared with existing design provisions.
A new RWFD design methodology is proposed providing a rational approach to improve performance in these unique buildings.