Seismic Propensity of Knee Braced Frame (KBF) as Weighed Against Concentric Braced Frame (CBF) Utilizing ETABS and OPENSEES
Mohammad Eyni Kangavar
Mohammad Eyni Kangavar, School of Civil, Environmental and Geological Engineering, Mapua Institute of Technology, Intramuros Street , Manila, Philippines.
Manuscript received on may 17, 2012. | Revised Manuscript received on June 12, 2012. | Manuscript published on June 30, 2012. | PP: 141-152 | Volume-1 Issue-5, June 2012 | Retrieval Number: E0454061512/2012©BEIESP

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Abstract: Steel braced frame is one of the structural systems used to resist earthquake loads in structures. Many existing reinforced concrete structures need retrofitting to overcome deficiencies and to resist seismic loads. The use of steel bracing systems for strengthening or retrofitting seismically in adequate reinforced concrete frames is a viable solution for enhancing earthquake resistance. Steel bracing is economical, easy to erect, occupies less space and has flexibility to design for meeting the required strength and stiffness. In the present study, seismic propensity of knee braced frames as weigh against concentric braced frames was investigated. These investigations were based on stiffness and ductility. Single – bay reinforced concrete frames in two levels which are a 1- story and a 10- story with three modes which are reinforced concrete frame without brace and reinforced concrete frame with concentric brace system and reinforced concrete frame with knee brace system were considered. Displacement analysis were performed using the Extended 3D Analysis of Building Systems (ETABS) software for investigating stiffness of these system and pushover analysis were performed through Open System for Earthquake Engineering Simulation (OPENSEES) software for investigating ductility of these system. Finally, analysis of cyclic loading was done by using again the OPENSEES software for the completion of the investigations. The results of these outputs indicated that concentric bracing can provide a stiffer bracing system but reduces the ductility of the reinforced concrete frame. Knee bracing can be employed to provide the desired ductility level for reinforced concrete frame. It is concluded that both concentric bracing and knee bracing systems may be used to design or to retrofit for a damage-level earthquake. However, when designing or retrofitting for a collapse-level earthquake, knee bracing is a more effective system. 
Keywords: Concentric braced frame, ductility, knee braced frame, stiffness.