Effect of Local Strengthening on the Overall Seismic Performance of Reinforced Concrete Frame Structures

The seismic performance of industrial and civil buildings is severely challenged by natural or man-made actions over a long period of time in service. Local strengthening is often carried out to avoid extensive strength reduction. However, current research primarily focuses on enhancing the mechanical performance of individual strengthened members, with little attention to the impact of local strengthening on the overall structure. In this study, the effect of layout symmetry on the overall seismic performance of a six-story reinforced concrete (RC) frame when locally strengthened by the strengthening bonding method is investigated by means of finite element analysis. Four strengthening schemes are considered: single-corner asymmetric, single-end asymmetric, quadrilateral symmetric, and central symmetric strengthening. The modal analysis confirms the enhanced stiffness in the strengthened structure. Asymmetric schemes yield uneven stiffness distributions, leading to pronounced vertical vibrations in higher modes. Conversely, symmetrical strengthening minimizes stiffness disparities through an optimized layout, yielding superior stiffness enhancements. The pushover analysis reveals a 53.6% increase in the lateral load-bearing capacity relative to the original configuration. Increasing the strengthening layers in symmetrical schemes further improves the lateral stiffness and performance reserve. However, when the number of strengthening layers exceeds four, the benefits become limited, and asymmetric strengthening significantly increases the inter-story drift ratio compared to its symmetric counterpart. Additionally, asymmetric strengthening leads to substantial lateral displacement discrepancies, thereby diminishing the overall structural coordination. Therefore, practical applications should adopt a holistic approach by favoring symmetrical strengthening and selecting an optimal number of strengthening layers to maximize the benefits.