EXPERIMENTAL AND ANALYTICAL STUDY ON THE BEHAVIOR OF STEEL PLATE SHEAR WALLS WITH BOX-SHAPED COLUMNS UNDER CYCLIC LOADING Nader Khajeh Ahmad Attari 1 , Mohammadhossein Akhavan Sigariyazd 2,* , Reihane Tavakoli 1 1 Structural Engineering Department, Road, Housing and Urban Development Research Center (BHRC), Hekmat Ave, Noori Highway, Tehran, Iran, 2 Department of Civil Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran.*Email: mhakhavan@mehr.sharif.edu ABSTRACT Steel plate shear walls are lateral load resisting systems consisting of vertical steel plate infills connected to the surrounding beams and columns. One of the parameters affecting the behavior of steel plate shear wall system under lateral load is characteristic of surrounding members. Since there are lots of experimental and analytical studies on steel plate shear walls with I-shaped surrounding members, this research is an experimental study carried out on a one-third scale steel plate shear wall system with box-shaped columns along with further analytical studies. The objectives were to calculate the stiffness, strength and energy dissipation capacity of the specimen and compare them with a very similar system constructed with I-shaped columns. Cyclic loading protocol of ATC-24 was used for test. Obtained experimental results showed a good conformity between box and I-shaped specimens. It is shown that the system can provide good initial stiffness and high ultimate capacity and remain intact under seismic effects. Some analytical studies on failure modes of system with box-shaped columns were also conducted using finite-element software confirming that the columns bottom connections and their flange buckling at that point are one of the most common modes of failure and a triangular reinforcing plate at that point can improve columns connection behavior effectively. KEYWORDS Steel plate shear wall, Box-shaped column, Cyclic behavior, Energy dissipation. INTRODUCTION According to the researches in recent decades, steel plate shear walls (SPWs) can be used as lateral load resisting system in high seismic hazard areas. The studies have revealed that this system has high initial stiffness, high elastic strength and behaves in a ductile manner (Driver et al. 1997; Caccese et al. 1993; Sabelli and Bruneau 2007) This system has been used in numerous buildings before advent of design requirements. The steel plate shear wall consists of steel plate surrounded by beams and columns; the most usual kind of this system is unstiffened walls recognized as special plate shear wall in AISC341 and ASCE7; the compression strength of these walls is very low so the shear buckling happens under low shear force and the lateral forces are carried by forming the tension field of the infill plate. Prior to key research in 1980s, the design limit state for SPW was considered to be out of plane buckling of the infill panel to prevent buckling; engineers designed SPW with heavily stiffened infill plates. At that time several analytical and experimental studies (Timler and Kulak 1983; Tomposch and Kulak 1987) showed that the post buckling strength and ductility of slender-web SPW can be substantial. This post buckling behavior is referred to as tension field action. Thorburn et al. (1983) developed a simple analytical strip model to represent the tension field action of a thin steel wall under shear load. This mechanism can be described as follows: When lateral load is applied to a steel plate shear wall, it is assumed that the shear panel just experiences the shear deformation so the shear infill plate is subjected to essentially pure shear with principle stresses (compression and tension) oriented at a 45 angle to the direction of load; as the slenderness of the plate (depth to the thickness ratio and width to the thickness ratio) is high, the buckling strength of the plate is very low, furthermore the plate will not be straight or flat initially due to the fabrication and erection tolerances so the plate buckles at low level of the force then lateral loads are transferred through the plate by principal tension stresses. Timler and Kulak (1983) verified and refined the strip model. The steel plate shear wall system which is designed properly and has specific details is so ductile and dissipate great amount of energy; the boundary element must be designed in such a way that allow formation of the tension field of the infill plate and its attainment to maximum capacity; so they play a key role in the accurate 739