Seismic performance assessment of steel bracing systems in high-rise reinforced concrete structures

Abstract

The seismic performance of Concentric Steel Bracing systems in modelled reinforced concrete (RC) frames is investigated. High-rise RC frames were designed and analysed based on Eurocode (EC) guidelines on Reinforced Concrete (EC2), Steel design (EC3) and Seismic design (EC8). Examination was performed in 3 stages: modelling and analysing a 20 story moment resisting frame, followed by 3 uniformly braced frames (both internally and externally) and finally a combined brace frame-whose bracing system was selected from the two best performing uniform systems. Parameters assessed were: story drifts and accelerations, joint displacements and accelerations, base reactions and story stiffness employing Modal Response Analysis. Results obtained pointed to several key achievements. Firstly, that capacity design was possible within set guidelines for high-rise structures. Based on the analysis parameters, absorption and dissipation of lateral forces was observed with increases in joint displacements and accelerations in the Z direction (perpendicular to ground motion). Correlative relationships linking story stiffness with story drift, and Story Stiffness with Joint Displacements and Accelerations were derived from data resulting from the analysis. Combining bracing systems produced marginal performance improvements compared to uniform concentric systems, and base reaction results showed that there was low improvement base shear and moments with the incorporation of braces.