Study on mechanical behavior of steel-UHPC-NC composite beams under negative bending moment

Abstract

To investigate the negative moment region flexural performance of a steel-ultrahigh performance concrete (UHPC)-normal concrete (NC) composite beam, steel-UHPC-NC composite beams with a uniform and cluster arrangement of studs and three push-out specimens were designed and fabricated. Based on the test results, the finite element model of steel-UHPC-NC composite beams was established and verified. The results of the study show that in the push-out test, the failure mode of the specimens is the shear failure of the stud, and the specimens with the NC-UHPC composite slab and UHPC slab are crushed and spalled at the root of the studs, but the damage extent and damage range of the specimens with UHPC slabs were significantly smaller than the NC-UHPC composite slab specimens. The load-slip response of the push-out specimen is obviously affected by the concrete slab material. The ultimate bearing capacity of the single stud of the steel-UHPC specimen, the steel-UHPC-NC stud single layer arrangement and the double-layer arrangement specimens were 249 kN, 158 kN and 192 kN, respectively. In the negative bending moment zone loading test, the development trend of the mid-span load–displacement curves of steel-UHPC-NC composite beams with uniform and cluster studs is consistent, with the cracks in the former concentrated at the mid-span position and the cracks in the latter concentrated near the nearest group of shear studs in the mid-span. The load–displacement curves of composite beams that studs are evenly distributed and studs are cluster type are consistent, with ultimate displacements in the span of 65.8 mm and 68.5 mm, respectively, and ultimate bearing capacities of 723.8 kN and 712.3 kN, respectively. The calculation results obtained by the simulation method are in good agreement with the test results, which could effectively predict the load–displacement response of the steel-UHPC-NC composite beam.