SEISMIC RETROFITTING OF REINFORCED CONCRETE (RC) BUILDING WITH STEEL BRACES

Abstract

In this paper an existing reinforced concrete (RC) building is identified and its seismic analysis and performance evaluation is done using the software SAP2000. Linear structural analysis and design of the building is done assuming building is built in lesser seismically active region, and thus the actual demand for the building is assumed to be higher than which assumed to be used in the analysis and design of the same. And this is done due to the inaccessibility of the reinforcing details of an existing building. Design of members are done using P-M (Axial load-Moment) interaction curves generated using MATLAB code as per IS 456-2000. Nonlinear static pushover analysis is done to figure out the capacity of the structure under seismic excitation and its performance is evaluated according to the provisions of ASCE 41-2013, and the inadequacy in capacity is rectified by adopting appropriate steel bracing configurations. Nonlinear analysis of bare frame structure showed that for DBE (Design Basis Earthquake) the damages undergone are within the limits of acceptance as per ASCE-41. I.e. the target displacement for DBE lies between IO (Immediate Occupancy) and LS (Life Safety), whereas for MCE (Maximum Considered Earthquake), it is beyond the acceptance limits of the structure. I.e. target displacement for MCE is out of CP (Collapse Prevention). Thus steel braces are adopted to enhance the performance of the structure. Here concentric bracing configurations are adopted and the locations of braces are optimized on the basis of inter-story drifts and performance. Cross sections of braces are also modified based on its strength and buckling analysis. The designer can make variations in layouts and patterns of bracing so as to get reasonable control of force flow in the retrofitted structure. Thus an adequate bracing configuration and brace location that suffices the performance objective of the structure is employed.