Assessment of seismic design parameters for midply wood shear wall system

A midply shear wall provides greater lateral load capacity per unit length than a standard shear wall. The improved performance is achieved by placing the sheathing between wall stud members, which subjects the nails to double-shear when the wall is loaded in shear. Tests have shown that the average lateral load capacities and energy dissipations of midply walls can be more than three times that of standard shear walls, while their stiffness can be between two to three times the average stiffness of standard shear walls. A proposal for implementation of the midply wall system in wood design codes in North America is presented. Non-linear dynamic analyses of a four-storey wood-frame building were used to determine the seismic design parameters for midply shear walls. The analysis utilized a suite of 22 selected earthquake records scaled to the peak ground acceleration stipulated in the National Building Code of Canada 2005 for Vancouver, British Columbia. The probability of failure was determined for building built with both standard and midply shear walls. Using the standard shear walls as the bench mark, this study indicates that a ductility-related force modification factor R d = 3 could be safely assigned for the midply shear wall system to achieve the same safety level as the standard shear wall system.