Effects of tension stiffening and shrinkage on the flexural behavior of reinforced UHPFRC beams

This paper presents a study on the flexural behavior of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) beams, which included conventional reinforcing bars. The study focuses on critical design aspects, such as concrete shrinkage and cracking implications on the tension-stiffening phenomenon. An experimental program with two different sized flexural reinforced UHPFRC beams was run. Beams were cast and tested in a four-point bending test (4PBT) using UHPFRC with different amounts of fibers: 130 and 160 kg/m³ (1.66% and 2.00% in vol.) to cover a wide range of strain-softening and strain-hardening constitutive UHPFRC behaviors. A non-linear finite element model (NLFEM) was developed to validate the mechanical tensile characterization of UHPFRC when applied to reinforced elements. Both shrinkage and tension-stiffening effects were considered to improve the model. After the NLFEM simulation, very reliable results were obtained at both the service and ultimate load levels compared to the experimental ones. Finally, some aspects about the design of reinforced UHPFRC cross-sections under bending forces are addressed and satisfactorily compared to the experimental results.