Eccentrically Loaded Square Concrete-Filled Steel Tubes Strengthened with CFRP Grid-Reinforced Engineered Cementitious Composite

Abstract

The use of carbon fiber–reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (CFGRE) systems to strengthen concrete-filled steel tubes (CFSTs) offers potential to improve the structural response as well as the resistance to high temperatures and corrosion. This study consists of an experimental investigation on the behavior of eccentrically loaded square CFSTs strengthened with CFGRE systems. Nineteen specimens were tested using a compression-testing machine with loads, deformations, and recorded test observations. The investigated parameters included the number of CFRP grid layers, width-to-thickness ratio of a steel tube, concrete strength grade, and eccentric ratio. The strengthened columns exhibited ductile failure. Due to stress concentrations, the CFGRE systems ruptured at the corners on the compression side. After strengthening, the yielding and ultimate loads of the CFST columns increased from 21.8% to 53.5% and 21.1% to 34.9%, respectively. Although an increase in the number of CFRP grid layers did not significantly affect the bearing capacities of the square specimens, it significantly enhanced the ductility of the columns. An increase in the eccentric ratio weakened the confining effect. An average decrease of 9.7%, 27.6%, and 41.4% was observed in the ultimate loads of the strengthened columns when the eccentric ratio increased from 0 to 0.1, 0.25, and 0.4, respectively. A five-point N–M interaction model was developed based on the principles of force equilibrium and deformation compatibility to predict the eccentric bearing capacities of strengthened columns. The prediction results exhibited high accuracy.