Size- and shape-effects analysis on the pure torsional performance of CFRP sheet-strengthened RC columns

To investigate the torsional performance of reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets, a mechanical analysis model was established using a three-dimensional numerical method. The model considered the heterogeneity of concrete, and the interactions between steel bars/CFRP sheets and concrete, simultaneously. The validity of the numerical model was first verified. Subsequently, pure torsion was added on 40 CFRP sheet-strengthened RC columns to investigate the influences of the fiber ratio, the structure size, and the cross-section shape on their torsional performance. Results showed that (1) size effect can be observed in the nominal torsional strength of both square and circular CFRP sheet-strengthened RC columns; (2) the size effect of square columns was stronger than circular columns due to weaker confinement effects of CFRP sheets on the square columns; (3) the addition of CFRP sheets can simultaneously improve the torsional strength and weaken the size effect, which is beneficial to the torsional performance of the column. Moreover, a torsional size effect law was proposed to predict the torsional strength of CFRP sheet-strengthened RC columns based on current simulation results.