Recommendations for Ω0 for Anchorage into Concrete for Floor-Mounted Nonstructural Components

Abstract

Relative to ductile anchors, nonductile anchors have long been subject to increased design safety margins in U.S. building codes for nonstructural building components. Historically, a safety factor was applied at the end of the calculation process, effectively modifying all elements within a given load case. This factor’s most recent implementations in the building codes narrowed its application to the horizontal earthquake component of the seismic load cases, taking the form of the overstrength factor, Ω, as a demand multiplier for nonductile anchor performance. From a rational combination of empirical observation and precedent, Ω was set to 2.5, but minimal experimental or analytical evidence exists to support this value. A research project was thus initiated with funding from Hilti Corporation at San Diego State University to study the overstrength approach through a combination of dynamic structural testing and nonlinear time-history analyses of an idealized nonstructural component with various anchor behaviors. The latter is presented in this paper, which made use of a customized analysis tool that allowed for rapid evaluation of unidirectional earthquake response for a wide range of component and anchor characteristics.