in most seismic building codes, the design base acceleration is computed using the natural period of vibration of the structure. Design specifications provide empirical formula to estimate the fundamental natural period of a system. In this study a class of steel plate shear walls, that have uniform properties through their height, was considered. The fundamental natural periods of this class of structures were determined using three dimensional geometrically linear finite element analyses and were compared against the estimates provided by seismic design specifications. Comparisons reveal that estimations using approximate formula can lead to unsatisfactory results. Based on this observation a simple hand method has been developed to predict the fundamental period of a steel plate shear wall. In the development of the hand method the steel plate shear wall has been recognized as a vertical cantilever for which simplified analytical solutions exist. Contributions of shear and bending stiffness of the wall have been explicitly taken into account. Furthermore, this simple method has been extended to dual systems having plate walls and special moment frames in the context of theories on wall-frame structures. Natural period estimations using the method that was developed in this study are compared with the finite element solutions and a good agreement is demonstrated. In addition, the effects of geometrical and material nonlinearities on the fundamental period were explored. The fundamental periods of steel plate walls were investigated at various drift levels. Based on the numerical analysis, elongation of the periods due to buckling and yielding of infill plates were quantified and are presented herein. (C) 2008 Elsevier Ltd. All rights reserved.