Equivalent Viscous Damping for Steel Moment-Resisting Frames with Cross-Laminated Timber Infill Walls

In the direct displacement-based design method, energy dissipative capacity of structures can be represented by an equivalent viscous damping (EVD). A number of studies have been reported in the formulation of EVD for different structural systems and hysteretic models. In this paper, an EVD model is developed and calibrated for steel-timber hybrid structures, where cross-laminated timber (CLT) shear panels are used as an infill in steel moment-resisting frames (SMRFs). To develop the EVD model, 243 single-story, single-bay CLT-infilled SMRFs analytical models are subject to semi-static cyclic analysis. Different model parameters of the hybrid structure are varied: gap between CLT panel and steel frame, bracket (connection) spacing, CLT panel thickness and strength, and postyield stiffness ratio of steel members. The EVD of each model was computed from the hysteretic responses based on an area-based approach. The design of computer experiments and response surface methodology were utilized to formulate the desired relationship between coefficients of EVD-ductility law and the model parameters. In order to create displacement compatibility between the equivalent linear system and time history, an iterative nonlinear time history procedure is adopted to calibrate the EVD-ductility law of the models. As a result, a new EVD-ductility law is presented that can be used in a displacement-based design of the steel-timber hybrid structure. (C) 2015 American Society of Civil Engineers.