Seismic Behaviour of UHM-CFRP-Strengthened RC Frame Buildings

Abstract Carbon fibre-reinforced polymer (CFRP) composites have emerged as an effective solution for enhancing the seismic performance of reinforced concrete (RC) structures. While previous studies have predominantly focused on the behaviour of CFRP-strengthened structural members, limited attention has been given to their influence on the global seismic response of RC frame buildings. This study evaluates the effectiveness of CFRP strengthening in improving the seismic performance of RC frame buildings with reduced concrete strength. 4-, 6-, 8-, and 10-storey RC frame buildings are designed using the Direct Displacement-Based Design (DDBD) methodology with a target inter-storey drift ratio (IDR) of 2%, based on the Eurocode 8 design response spectrum corresponding to a peak ground acceleration (PGA) of 0.45 g and a damping ratio of 5%. Numerical models of CFRP-strengthened beams and columns are validated against published experimental results. Buildings designed with M25 concrete are considered as the reference models, and the concrete grade is subsequently reduced to M20, M15 and M10 to simulate strength deterioration. Nonlinear time-history analyses are carried out using spectrum-compatible ground motions. Based on the analytical results, empirical equations are developed to predict the IDR ratio and building stiffness ratio as functions of concrete grade and are validated using independent building models with different plan configurations and heights. The results indicate that CFRP strengthening considerably reduces inter-storey drift and increases the lateral stiffness of RC frame buildings, particularly for buildings with lower concrete strength. The proposed equations provide a practical and reliable tool for estimating the seismic response of CFRP-strengthened RC buildings.