Shear Behavior of Reinforced UHPC Considering Fiber Alignment and Axial Load Effects

This research study investigated the axial load and fiber alignment effects in the shear behavior of Ultrahigh-Performance Concrete (UHPC) panels incorporating reinforcing bars. Three UHPC panels were tested on the Universal Panel Tester (UPT) facility. The UHPC panels were subjected to pure shear and combinations of shear with axial compression and tension. Panel test results were complemented with fiber alignment analyses using samples extracted from the panels and companion direct tension test (DTT) specimens. Applying an axial tensile load ratio of 33% reduced the shear strength of the panels by 12.3%, whereas an axial compressive load ratio of 5% enhanced the shear strength by 77.6%. Fiber alignment analyses indicated that boundary effects induced by the reinforcing bars caused a reduction in the fiber alignment factor by as much as 38.1% relative to the DTT specimens. The experimental findings were incorporated into the Softened Membrane Model for UHPC (SMM-UHPC) to simulate the panel shear responses. Combining experimental and numerical results demonstrated that modeling of UHPC shear requires the use of appropriate ratios to represent the relative alignment of fibers between structural members and companion DTT specimens. Fiber alignment effects were included in SMM-UHPC by modifying the constitutive tensile behavior of UHPC with a fiber alignment ratio of 0.72.