Steel-concrete composite beams strengthened with NSM CFRP systems at the hogging-moment regions

Compared with conventional strengthening methods, the near-surface mounted (NSM) technique is more suitable for strengthening steel-concrete composite beams, especially at the hogging-moment regions. This paper investigates the flexural performance of steel-concrete composite beams strengthened with NSM CFRP systems. Four-point bending tests are carried out on four composite beam specimens, including one control beam without strengthening and three strengthened beams with NSM CFRP systems. The failure mode, ultimate load-carrying capacity, deflection distribution, and material strain distribution of the composite beams are presented, based on which the effects of the anchorage method and the number of CFRP bars are studied. The test results demonstrate that the main failure mode of the strengthened beams is the buckling of the steel beam. Compared with the control beam, the load-carrying capacity of the strengthened composite beams with two and four CFRP bars is increased by 10% and 20%, respectively. The use of end anchorage has a slight effect on the flexural capacity of the strengthened beams, while significantly improves the ductility during the later stage of loading. In addition, a nonlinear finite element (FE) model is proposed and calibrated, based on which a parametric study is performed to investigate the effects of the length and section area of CFRP bars, the spacing of grooves, and the thickness of bottom steel flange on the ultimate load-carrying capacity of the strengthened beams.