Parametric experimental characterization of synergistic effects of fire protection layers on the performance of strong-wood shear walls

Abstract

In highly seismic countries such as Chile, codes impose strict drift limits to control earthquake damage. Quantifying the contribution of non-structural layers, particularly Type X Gypsum Wallboard (GWB), is therefore critical for light-frame timber buildings (LFTB). Beyond fire protection, Type X GWB can increase the lateral strength and stiffness of Strong Shear Walls (SSWs), a high-capacity shear-wall configuration developed for mid-rise LFTB. This study evaluates Type X GWB effects on Multi-Layered Strong Shear Walls (MLSSWs), defined here as SSWs where the structural OSB sheathing and one or more Type X GWB finish layers are fastened to the same framing so that the layers resist in-plane loads in parallel. Eighteen cyclic tests were conducted, considering screw- or staple-fastened Type X GWB, two aspect ratios (1:1 and 2:1), two OSB edge-nailing patterns (100 mm and 50 mm), and varying numbers of Type X GWB layers. For shear-governed configurations, Type X GWB increased strength by up to 64 % and initial stiffness by up to 79 %. Staple-fastened assemblies performed comparably to screw-fastened ones, offering a cost-effective option for fire-rated walls. In contrast, for rocking-dominated shear walls or shear walls with dense nailing, the Type X GWB contribution was markedly reduced. Building-level numerical modeling then assessed global effects, indicating fundamental-period reductions and lateral-drift reductions of up to 18.5 % and 34 %, respectively. These findings expand the experimental evidence base and support future efforts to evaluate whether fire-protection finish layers may be recognized in the seismic design and assessment of timber shear walls.