CLT–Steel Hybrid System: Ductility and Overstrength Values Based on Static Pushover Analysis

Abstract

A timber-steel hybrid system, where cross-laminated timber (CLT) shear panels are used as infill in steel moment resisting frames, is analytically investigated. The proposed hybrid system combines ductile behavior of steel moment frame with lighter and stiffer CLT panels. Initial parametric study is carried out with a single-bay-single-story model using pushover analysis to investigate effect of CLT panel thickness, crushing strength, and confinement gap. Results showed that the parameters studied have a significant influence on system’s ultimate strength, ultimate drift capacity, and post-peak behavior. Subsequently, parametric studies are carried out for three-bay hybrid buildings with three-, six-, and nine-story hybrid buildings for varying panel configuration (a given gap, panel thickness, and crushing strength) values. The parameters varied and are design ductility level (limited ductility and ductile) and infill pattern. A monotonic pushover analysis was performed to develop a preliminary ductility and overstrength values based on both steel yield of frame and panel crushing force in the links. Overall, the results suggest that addition of infill bays is less beneficial in ductile moment frames; CLT infill panels are better suited to lower ductility systems. Ultimately, a ductility factor of 2.5 is recommended for the infilled frame system, and an overstrength factor of 1.25 appears to be warranted.