Investigating the Capacity and Stiffness of Joints used in Gypsum Wallboard Sheathed Light-Frame Wood Shearwalls

Abstract

The provisions to determine the deflection of gypsum wallboard (GWB) sheathed shearwalls available in the Canadian and American standards are limited to nailed shearwalls and are rudimentary compared to the wood based sheathing equations. There is currently no fastener slip model for the GWB sheathed shearwalls that are fastened with GWB screws. A main goal of this study is to improve the existing equations for nailed GWB sheathed shearwalls and develop a suitable analytical expression that can be used for GWB fastened with screws. In total, 270 GWB sheathed joints were subjected to reversed cyclic loading with variations including GWB type, thickness, fastener type, fastener size and manufacturers. The power model type is used to develop the fastener slip equations for nails and screws, which have GWB density and fastener diameter as equation inputs. The accuracy of the developed model is then validated by comparing the tested full-scale GWB sheathed shearwall deflection to the deflection calculated using the newly proposed fastener slip models. The proposed equation is a significant improvement to the existing code provisions. Component testing was performed on the fasteners (center point bending test) and the GWB (dowel bearing test). The results of these tests were used to determine the joint capacity based on the European Yield Model. It was also found that the shearwall capacity could be predicted by considering the joint level capacity while accounting for the number of joints at a panel edge. The joint level and full-scale experimental results are also validated with the use of an analysis program (SAPWood) to model the joint level hysteresis as a hysteretic spring with 10 model fitting parameters. The developed joint level hysteretic model was then used to represent the fasteners connecting the sheathing panels to the lumber framing in the construction of the full-scale shearwall model.