Nonlinear seismic responses of a typical 15-storey and 4-storey steel plate shear wall are studied. Dynamic shear and moment envelopes are compared with the current CAN/CSA-S16-01 seismic capacity design approach. It has been observed that estimated dynamic base shear forces and overturning moments in the steel plate shear walls, as well as the column forces, are underestimated in the current seismic design provisions. The effect of loading rate on the dynamic behaviour of steel plate shear walls is also investigated. Nonlinear dynamic analyses show that loading rate increases flexural demand mostly at the base of the steel plate shear wall and loading rate has a small effect on inelastic seismic demand for a suite of spectrum compatible earthquake records for Vancouver. Also investigated is the P –delta effect on seismic demand in shear and flexure. The inelastic seismic analyses indicate that the current National Building Code of Canada stability factor approach to account for P –delta effects is very conservative for steel plate shear walls and the P –delta effects on seismic demand are very small.