Comparative study on flexural behavior of steel-UHPC composite beams and steel-ordinary concrete composite beams in the negative moment zone

Abstract

To compare the flexural behavior of steel-UHPC (ultra-high performance concrete) composite beams and steel-ordinary concrete composite beams under a negative bending moment, 4 steel–concrete composite beams were tested under a negative bending moment. The effects of slab materials and stud number on flexural failure mode, crack development, stiffness ductility, cracking load and ultimate flexural capacity of composite beams were investigated. The results show that the UHPC can significantly improve the flexural behavior of steel–concrete composite beams under a negative bending moment. For the steel-UHPC composite beams with a single row, the cracking load is 135 % higher than that of steel-ordinary concrete composite beams, and the overall stiffness increased by 108 %, the yield stiffness increased by 40 %, the ultimate flexural capacity increased by 9 %, and the ductility increased by 133 %; for the steel-UHPC composite beams with double row, the cracking load is 102 % higher than that of the steel-normal concrete composite beam, the overall stiffness is increased by 34 %, the yield stiffness is increased by 44 %, the ultimate flexural capacity is increased by 6 %, and the ductility is increased by 75 %. Increasing the number of studs can significantly improve the overall ductility of composite beams, while the improvement of cracking load, overall stiffness, and ultimate flexural capacity of composite beams is not significant. The cracking load, overall stiffness, yield stiffness, ultimate load, and ductility of double-row stud steel–concrete composite beams are 23 %, 53 %, 13.2 %, 12 %, and 115 % higher than those of single-row stud steel–concrete composite beams, respectively; while those of double-row steel-UHPC composite beams increases by 6 %, 8 %, 16 %, 8 % and 62 % higher than those of single-row stud steel–concrete composite beams, respectively. A simplified calculation model for the flexural capacity of steel-UHPC composite beams in a negative moment zone was established.