Evaluation of system effects in light frame timber buildings through a shake table test

Abstract

Light Frame Timber Building (LFTB) is one of the new structural systems currently evaluated by the Chilean construction industry, public authorities, and academia to enhance the sustainability of the Chilean midrise building inventory. When designing LFTBs in high seismic risk areas, large overturning moments are common because of the light self-weight of wood and the often-dominant rocking flexibility of shear walls. Therefore, evaluation of the cumulative effects (i.e., cumulative overturning rotation and bending deformation) and the lateral response considering the true behavior of shear walls is essential to realistically assess story drift demands and inertial forces. In addition, current mechanical models suffer from several limitations when attempting to model the LFTB response. Among others, they do not consider overturning reduction due to system effects. Here system effects refer to: a) the effect of transverse walls in non-planar shear wall configurations; b) out-of-plane bending diaphragm interaction with the shear walls; and c) gravity load. This paper presents part of the findings of a shake table test on a 3-story, 1:2 scale LFTB, examining the influence of system effects. The study contributes to the comprehension and quantification of system effects, highlighting the benefits of component interaction in LFTBs subjected to lateral loads. Test results demonstrate that system effects significantly reduce story drift demands by increasing the building’s lateral stiffness and damping ratio compared to cases where component interaction is neglected. For instance, the first-floor secant stiffness in the experiment was higher than the predicted value assuming planar shear walls. This underestimation decreases at higher stories in the building, indicating that the gravity load further enhances the benefits of transverse shear walls and out-of-plane bending stiffness interaction. These findings have implications for the design and analysis of LFTBs in seismic regions, promoting their widespread adoption as a sustainable and resilient construction solution.