Seismic design of FRP grid and bar strengthened RC columns via multi-objective optimization and decision analysis

Abstract

Seismic retrofit of reinforced concrete (RC) columns is essential for structural safety during earthquakes. However, using fiber-reinforced polymer (FRP) grids and embedded FRP bars makes it difficult to achieve high ductility, low residual drift, and acceptable cost simultaneously. This study develops a multi-objective optimization framework that couples a calibrated fiber-based finite element (FE) model with the Multi-Objective Evolutionary Algorithm based on Decomposition (MOEA/D) to maximize ductility and minimize residual drift ratio (RDR) and material cost. The FE model is validated against cyclic tests on FRP-strengthened RC columns, and the framework produces well-distributed Pareto fronts within 60 generations. An energy-based regression model relates RDR to the hysteretic energy dissipation ratio and residual slip and crack components, identifying the energy dissipation ratio as the dominant factor. Under a design-level seismic loading, Pareto-optimal results show that engineered cementitious composite (ECC) jackets with basalt-FRP (BFRP) grids increase ductility by 26.4%, whereas carbon-FRP (CFRP) grid-and-bar systems reduce residual drift by up to 32.1% relative to a reference FRP grid-polymer cement mortar (PCM) retrofit. Low-cost BFRP grid-PCM schemes still provide moderate ductility and stable hysteretic responses. The proposed framework clarifies quantitative trade-offs among ductility, residual drift, and cost, and offers engineering guidance for designing efficient, performance-based seismic retrofit strategies for existing RC columns.