The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 1 Theoretical Seismic Behaviour of Steel Plate Shear Walls Fariborz Nateghi 1 and Erfan Alavi 2 1 Professor, Dept. of Structural Engineering, International Institute of Earthquake Engineering and Seismology, IIEES, Tehran, Iran 2 PhD Candidate, Dept. of Structural Engineering, International Institute of Earthquake Engineering and Seismology, IIEES, Tehran, Iran Email: Nateghi@iiees.ac.ir , E.Alavi@iiees.ac.ir ABSTRACT: In the last three decades, many researches have been carried out on steel plate shear walls, SPSWs, and they have been introduced as seismic load resisting systems. However, their non-linear behaviour complexities such as buckling, post buckling and tension field action of infill steel plate, in-elastic out-of-plane large deformation of steel plate, hysteresis loops, interaction with the surrounding frame, several configurations of SPSWs with thick plates, stiffened or un-stiffened thin steel plates, etc., have made them still attractive for more investigation. This paper presents shear strength capacities and proposes relevant formulas for SPSWs with and without stiffeners with considering effects of the relative stiffness and strength of the boundary elements on the shear capacities. Several analytical finite element models with different h/t of steel plate are considered and kinematic hardening model is used for steel material, non-linear large-displacement analysis under monotonic loading has been carried out and their push-over curves obtained. The results are compared with the experimental studies by other researchers and codes regulations. The theoretical and analytical studies indicate that the shear strength capacities of SPSW vary between results from using the plate girders simulation model for SPSW and the strip model, and depend on the relative stiffness and strength of the boundary elements as well as the slenderness of the infill steel plate. KEYWORDS: Steel Plate Shear Walls, Plate Girders, Push-Over, Strip Model, Boundary Elements 1. INTRODUCTION Recent researches have demonstrated that steel plate shear walls, SPSWs, can act as effective and economic seismic load resisting systems in the high risk zones. SPSWs have high elastic stiffness, large displacement ductility, and stable hysteretic behaviour and high energy dissipating capacity. They have been used in the structural design and retrofitting of existing buildings with different configurations, with thick steel plate, stiffened or un-stiffened thin steel plate. Use of thick steel plates or stiffened still plate in SPSW intends to conduct the steel plate to its full plastic strength prior to the elastic out-of-plane buckling of the plate and to prevent tension field action from developing in the infill plate , however, in un-stiffened SPSW with thin infill steel plate the post buckling strength of the infill steel plate due to tension field action development in the steel plate after the elastic out-of-plane buckling is main part of the shear strength capacity of the system. The history of SPSWs returns to the plate girders, and the analogy that simulates the columns of a SPSW to the plate girders flanges and the beams to the stiffeners and the infill plate to the plate girder web is appropriate for general understanding of the system behaviour, however, it does not completely represent the behaviour of the SPSW, especially the non-linear and cyclic performance of the system. The differences mainly result from the boundary elements effects on the system responses. Many theoretical and experimental investigations have been