Numerical investigation and design of CFST columns strengthened by CFRP grid-reinforced ECC under eccentric compression

Carbon fiber-reinforced polymer (CFRP) and engineered cementitious composites (ECC) have become universal materials for strengthening structural members, and their effectiveness in improving the mechanical behavior of concrete-filled steel tube (CFST) columns has been verified by experiments in previous studies. However, how the CFRP, ECC and CFST columns work together, and the mechanical mechanism of the strengthened column is still unclear. Therefore, to further reveal its mechanical behavior and working mechanism, combined with the experimental results of the CFST columns strengthened with CFRP textile grid-reinforced ECC, a detailed numerical analysis was conducted based on a series of finite element (FE) models in this paper. The load-displacement curve, N-M curve, lateral displacement, stress distribution, the contribution and influence degree of each part of materials to the load-bearing capacity of the strengthened columns were investigated. Finally, taking into consideration the confinement effects of the CFRP grid and the ECC on concrete, a novel theoretical model was established and verified. As a result, the concrete contributes approximately 60% to the peak load of the strengthened column. Under small eccentricity ratio, the mechanical behavior of the CFRP grid can be fully realized. The yield strength of the steel tube and the compressive strength of the concrete have a highly significant effect on enhancing the load-bearing capacity of the strengthened column. The theoretical model proposed in this study can accurately predict the load-bearing capacity of the strengthened columns under eccentric compression, thus offering valuable insights for the design and research of such strengthened columns.