Flexural performance of HSS-UHPC composite beams with perfobond strip connectors

Considering the influence of different shear connection degrees, the mid-span two-point symmetrical loading tests for three pieces of high strength steel (HSS)-ultra-high performance concrete (UHPC) composite beams using perfobond strip (PBL) connectors were conducted to evaluate the flexural performance of HSS-UHPC composite beams. The properties including flexural rigidity, deflection, interfacial slip, and strain distribution laws of HSS-UHPC composite beams were analyzed under the shear connection degree of 1.02, 0.89, and 0.76, and the overall performance of steel beams and UHPC plates was discussed. In addition, the failure mechanisms of the beams subjected to bending moments were analyzed. On the basis of the ABAQUS nonlinear finite element numerical models for the HSS-UHPC composite beams, the matching relationships among concrete strength, plate thickness, and steel strength were investigated, and the feasibility of existing simplified plasticity theory in calculating the flexural performance of the HSS-UHPC composite beams was evaluated. Research results indicate that the HSS-UHPC composite beams using PBL connectors have the favorable flexural capacity and large plastic deformability, and their flexural rigidity and ductility are qualified for engineering applications. For the composite beams in the elastic stage, the relative interfacial slip between UHPC and HSS develops slowly, and the maximum slip occurs near the 1/8 of the beam. In the plastic stage, the interfacial slip rises rapidly, and the maximum slip section gradually moves to the beam ends. The flexural performance of HSS-UHPC composite beams is significantly affected by the shear connection degree. When the connection degree decrease from 1.02 to 0.89 and 0.76, the initial flexural rigidity of the composite beams lowers by 7.0% and 8.7%, respectively, and the corresponding ultimate bearing capacity decreases 9.2% and 14.6%, but the maximum slip grows by 15.8% and 17.0%, respectively. Good agreement is found among the numerical, experimental, and theoretical results. Numerical result demonstrates that after the replacement of Q460 steel with Q690 steel for the composite beams, the flexural capacity sees an increase of 29.0%, but the ductility decreases by 39.7%. The ductility and flexural capacity of the HSS-UHPC composite beams can be improved by higher UHPC strength and thicker concrete plates.