EQUIVALENT ELASTIC MODELING FOR THE DIRECTDISPLACEMENT-BASED SEISMIC DESIGN OF WOOD STRUCTURES

Direct-displacement seismic design assumes that the response of a structural system can be obtained through a single-degree-of-freedom (SDOF) model with equivalent elastic lateral stiffness and viscous damping properties representative of the characteristics of the structure at a target displacement. To date, this assumption has not been validated for structures exhibiting highly pinched hysteretic response, as is typical of wood structures. This paper presents and discusses the results of an extensive numerical investigation aimed at assessing the equivalent linear modeling of light-frame wood buildings. The findings from this study indicate that elastic models, based on equivalent viscous damping representative of first cycle hysteretic response, with no pinching behavior, under-predict by 20% on average the seismic response of fully non-linear models. On the other hand, elastic models, based on equivalent viscous damping representative of hysteretic cyclic response past the first (virgin) cycle, with pinching behavior present, over-predict significantly (40% on average) the seismic response of fully non-linear models. Various approaches are briefly presented to show how the response differences between equivalent linear elastic and fully inelastic building models can be taken into account in the direct-displacement based seismic design procedure for light-frame wood buildings.