Steel plate shear walls with outriggers. Part I: Plastic analysis and behavior

Steel plate shear walls (SPSWs) are ductile and economical energy dissipating systems for buildings located in regions of high seismic risk. In spite of many advantages of SPSWs; however, their overturning stiffness is relatively low, especially when their width is narrow compared to the building height. Therefore, additional flexural stiffness must be provided to the system when designing narrow SPSWs. A logical solution that can be effectively used in SPSW systems is to rigidly connect the beams of adjacent bays to the columns of SPSWs (on both sides) forming an interacting system of SPSW and moment frame in which the adjacent beams act as outriggers resulting in an overall reduction of overturning in the SPSW. However, insufficient information exists on the behavior and efficiency of such structural systems, herein referred to as SPSW with outriggers (SPSW-O). This paper discusses four different potential SPSW-O options that can be used in mid- to high-rise buildings to enhance the flexural stiffness of the system. Plastic mechanisms, ultimate lateral load resistance and overturning stiffness of such systems are investigated, and key design parameters are identified through a combined analytical and numerical investigation. A parameter called the outrigger efficiency factor (OEF) is defined to quantify the contribution of the outrigger system to the overall overturning stiffness of a SPSW-O. Analytical expressions are derived for the lateral load resistance and OEF of the four SPSW-O options, and are then compared with numerical analysis results with reasonable agreement. Furthermore, parametric studies are performed to investigate the influence of a number of parameters on the overall behavior and characteristics of the SPSW-O systems. Parameters subject to investigation include height of the wall, outrigger beam and connection properties.