Evaluation of Out‐of‐Plane Wall Anchorage Force Provisions in Buildings with Rigid Walls and Flexible Roof Diaphragms

Heavy concrete and masonry walled buildings with lightweight steel or wood flexible roof diaphragms are a common type of construction in North America. Failures of the out‐of‐plane wall anchorage to these roof systems and the resulting partial roof collapses during past earthquakes have led to repeated revisions to the seismic design provisions in the U.S. model building codes. However, the force levels considered in the current design provisions have remained largely unchanged since their introduction in the 1997 Uniform Building Code, and these provisions have not been fully tested by strong ground motions in the field. Using a two dimensional numerical framework, a series of nonlinear time history dynamic analyses on various building archetypes were conducted to evaluate the validity of the current wall anchorage design force levels. The results of this study reveal that the current wall anchorage design forces are generally appropriate, but with some very significant exceptions.