Recent studies have demonstrated the effect of earthquake ground motion duration on structural collapse capacity. They have also proposed methods to explicitly account for this effect of duration in structural design and assessment procedures via an adjustment to the design ground motion intensity. The objective of this study is to explore an alternative method to account for the effect of duration by adjusting the permissible peak deformations instead. This study investigates the effect of ground motion duration on the dynamic deformation capacity of modern-ductile reinforced concrete and steel framed structures. To this end, a method is proposed to evaluate the structural dynamic deformation capacity, associated with collapse, through incremental dynamic analysis. The proposed method is then utilised to investigate the correlation between dynamic deformation capacity and ground motion duration. Preliminary results indicate a reduction in the dynamic deformation capacity of the analysed structures under the increased cyclic demands imposed by long duration ground motions. These results will be assimilated to propose a modification to the peak deformation acceptance criteria employed by seismic design and assessment procedures to explicitly account for the effect of duration.