Prefabricated Composite Steel-Timber Stiffened Wall Systems with Post-Tensioning: Structural Analysis and Experimental Investigation under Vertical Axial Load

Abstract

With increasing demand for midrise buildings, automated prefabrication, design for manufacturing and assembly (DfMA), and sustainability, a novel material-efficient post-tensioned (PT) composite steel-timber (CST) stiffened wall system has been developed. As opposed to cross-laminated timber (CLT), this fully prefabricated panelized composite system consists of an engineered wood panel that is integrally stiffened by timber studs and steel square hollow sections (SHS). Each SHS additionally accommodates a PT rod and panel-to-panel connections, allowing for quick onsite assembly, permanent tie-down, and self-centering inverted pendulum rocking. This study presents and evaluates the structural buckling behavior and performance of these systems under vertical axial loading in terms of failure modes, serviceability, ultimate limit states, midheight out-of-plane deflection along the width of the wall, and PT force loss. This has been achieved through an extensive experimental investigation and analysis consisting a total of 10 PT-CST stiffened walls with multiple variables including level of post-tensioning, wall height, end conditions, and the connection between the panel and SHS and the panel and stud stiffeners. Complex behavior through several modes of failure was observed with the increased application of initial PT force, which in turn reduced the ultimate capacity. Additionally, it was found that PT force reduction due to vertical axial loading even within the serviceability limit state (SLS) is significant. Thus, it is recommended that this reduced PT force be considered in design.