ASCE 41 Backbones in Concrete Building Evaluation

The ASCE/SEI 41-23 standard, Seismic Evaluation and Retrofit of Existing Buildings, commonly known as ASCE 41, uses a performance-based earthquake engineering approach that describes ductile component (such as beam or column) inelastic behavior via a so-called backbone curve. ASCE 41 modeling and acceptance criteria for ductile components are based on backbones derived from quasi-static lab tests, which can have different outcomes depending on the loading pattern. Customary testing uses standard protocols involving numerous symmetrical, fully reversed cyclic displacements, which are more severe than the loading patterns induced by actual earthquakes. This paper examines the effects of using backbones that reflects more realistic (or representative) earthquake demands on the computed story drift responses from dynamic analyses using a simplified building model having a typical column yielding mechanism found in archetype ductile four-story reinforced concrete moment frame buildings. Investigated are the effects of backbone modeling variations including strength, stiffness, ductility, and hysteretic pinching. It is also demonstrated that the cyclic degradation modeling commonly used in adaptive modeling can have a negligible effect on the seismic behavior of structures with ductile components. While it is reasonable to expect the trends observed in this study to apply to similar ductile components, caution is advised when extending these findings to older, nonductile buildings, as the trends may not be applicable.