Seismic response of steel frames with knee braces

The use of steel bracing systems for upgrading seismically insufficient structures is a feasible solution by enhancing the global stiffness and strength of such structures. Moreover, steel bracing systems have relatively low cost and easy construction phases. For this purpose, several configurations of steel bracing systems can be applied for upgrading the seismic behavior of the structures. The most frequently utilized systems comprise concentrically-braced frames, eccentrically-braced frames, and knee-brace frames [1]. In the last few decades, the seismic behavior and design of new steel structures with knee bracing systems has been studied extensively due to its efficiency as an earthquake resisting system [2-8]. Indeed, the structures with knee bracing can be designed to be stiff enough to control structural and nonstructural damage, and ductile enough to prevent sudden collapse. In order to achieve these purposes, the lateral stiffness is provided by the brace elements and ductility by the knee elements through the formation of plastic behavior for dissipation of the energy under earthquakes. In the current study, apart from the studies in the literature, the effectiveness of using different types of knee bracing systems, such as chevron, cross and diagonal knee bracing systems for enhancing the seismic response of the existing steel moment resisting frame systems were comparatively examined through nonlinear time history analysis.