Experimental, analytical, and numerical investigation on flexural behavior of the gradient UHPC-NC composite beams

To enhance the deformation resistance of concrete beams, the flexural behavior of eight gradient ultra-high performance concrete (UHPC)-normal concrete (NC) composite beams was experimentally studied. The effects of different gradients and fiber types on the deflection of the gradient UHPC-NC composite beams were investigated, and a deflection calculation method for the composite beams was proposed. Finally, numerical simulations were conducted on the basis of the cohesion models. Results indicate that the gradient UHPC design significantly improves both the loading-bearing and deformation capacity of the composite beams. The cracking load of the gradient composite beams with steel fiber-UHPC at the bottom layer is much higher than that of the beams with basalt fiber-UHPC, and the number of cracks in the pure bending section of the beams with steel fiber-UHPC at the bottom layer is remarkably less than that of the beams with basalt fiber-UHPC at the bottom layer. However, their ultimate capacities were comparable, indicating that steel fibers can effectively improve the fracture toughness of UHPC. The predicted deflection of the gradient UHPC-NC composite beams agrees well with the test results, indicating the accuracy of the proposed deflection model. The bearing capacity and deflection obtained from the numerical simulation also align well with the test results.