International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 02 Issue: 06 | Sep-2015 www.irjet.net p-ISSN: 2395-0072 © 2015, IRJET ISO 9001:2008 Certified Journal Page 40 STUDY ON SEISMIC BEHAVIOR OF KNEE BRACED STEEL FRAMES Anitha M. 1 , Divya K.K 2 1 M.Tech Scholar, Dept of Civil Engg., SNGCE, Kerala, India 2 Asst. Professor, Dept of Civil Engg., SNGCE, Kerala, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract-Steel has become the predominate material for the construction of bridges, buildings, towers and other structures. Its great strength, uniformity, light weight and many other desirable properties makes it the material of choice for numerous structures such as steel bridges, high rise buildings, towers and other structures. The advantages in general credited to steel as a structural design material are high strength/weight ratio ductility, predictable material properties, speed of erection structures, quality of construction, ease of repair, adaptation of prefabrication, repetitive use, expanding existing structures and fatigue strength. Steel structures in areas prone to high seismic activity should satisfy two main conditions. It should be stiff enough to control the drift to prevent structural damage, and also must have sufficient ductility to prevent collapse caused by dramatic deformation. Bracing element in structural system plays vital role in structural behavior during earthquake. Steel bracing is an effective and economical solution for resisting lateral forces in a framed structure. Knee braced steel frame is that which has got excellent ductility and lateral stiffness. Since the knee element is properly fused, yielding occurs only to the knee element and no damage to major elements. Compared to other type of bracings it performs better during a seismic activity. In this study the seismic effect of different types of steel bracings was studied. A comparison of knee braced steel frame with other types of bracings had been done. Performance of each frame had been studied using non-linear static analysis and non linear time history analysis. Various parameters such as displacement and stiffness were studied. Key Words: Steel bracing, Non linear static analysis, Non linear time history analysis. 1. INTRODUCTION Steel has become the predominate material for the construction of bridges, buildings, towers and other structures. Its great strength, uniformity, light weight and many other desirable properties makes it the material of choice for numerous structures such as steel bridges, high rise buildings, towers and other structures. Bracing element in structural system plays vital role in structural behavior during earthquake. Steel bracing is an effective and economical solution for resisting lateral forces in a framed structure. Bracings are of different types, namely concentric bracings, eccentric bracings and knee bracings. In concentric bracings, inelastic energy dissipation response is generally poor due to the possible buckling of the diagonal elements in compression. In eccentric bracings since it absorbs large seismic force, repair and replacement after a severe earthquake is expensive and time consuming. As a remedy for all these disadvantages knee braced frame developed. Frames with knee bracings (KBFs) provides an effective bracing solution. It can be obtained by providing a new element called "knee" in between the beam and column along with bracings. These bracings limits interstorey drifts, and knee element absorbs the earthquake energy, by providing cyclic deformations in shear or bending. The main advantage with respect to eccentric braced frames is that damage is concentrated in secondary element and it can easily replaced after destructive earthquakes. The position and stiffness of knee was the most important factor affecting the lateral resisting ability of KBF.The beams and columns got great influence on the lateral behaviour of KBF structure[6]. The knee element will yield first without affecting the other main structural elements[7]. Fig -1: Knee bracing