In this report, a test program to evaluate the seismic performance of shear walls using wood screws as mechanical fasteners is presented. To estimate the mechanical properties of wood screws which are available on the Canadian market, different brands of wood screws with different diameters and lengths were purchased from major building material suppliers in Vancouver area, BC. The screw bending, joint and full-scale shear wall tests under monotonic and reversed cyclic loading were conducted. The findings from the test results are summarized as follows:
1. The average yield strength is 712 MPa for gauge No. 6 screws and 845 MPa for gauge No. 10 screws. For both gauge No.6 and No.10 screws, the variation of yield strength is around 11%. The average modulus of elasticity (MOE) is 30337 MPa for gauge No. 6 screws and 37129 MPa for gauge No. 10 screws. For both gauge No.6 and No.10 screws, the variation of MOE is around 22%.
2. For joints with same gauge screws, the capacities of joints with different lengths of screws are similar. The maximum displacements of screw joints under cyclic loading are much less than those under monotonic test. This is because the screws were broken under reversed cyclic loading.
3. For shear walls with the same gauge wood screws, shear walls with different screw lengths had similar lateral load capacities and ultimate displacement under cyclic loading. The ultimate displacement is over 75 mm under monotonic loading and around 50 mm under cyclic loading. Compared to shear walls with common nails, shear walls with wood screws had similar ultimate displacements under monotonic loading, and smaller maximum displacements under cyclic loading. The reduced ductility is due to the fracture of screws under cyclic loading.
4. Based on the test results, it is recommended that a ductility-related seismic force modification factor, Rd, of 2.0 be used for the design of wood shear walls with wood screws. This claim needs to be validated through the use of a series of non-linear dynamic analyses. To ensure that screws do not break under seismic load, it is recommended that the inter-storey drift for wood shear walls with screws be limited to 1.6% of the storey height.
