Flexural performance of functionally graded UHPFRC-NSC beams

This paper presents an experimental and numerical study on the flexural performance of Functionally Graded Reinforced Concrete (FGRC) beams using Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) with Normal-Strength Concrete (NSC). The experimental results were used to examine the applicability of the codes’ predictions of flexural capacity adopted in ACI 318-2019, EC-2, and ECP-203-2020. The flexural design recommendations of AFGC-2013, JSCE-2008, and KCI-2012 were also examined. The experimental program involved ten simply supported beams with identical cross-sectional dimensions and two different tensile reinforcement ratios (ρl = 1.38 % and 5.68 %). FGRC beams consisting of UHPFRC (with fcu = 174.3 MPa) and NSC (with fcu = 45.8 MPa) were tested under four-point bending. The layer of UHPFRC was positioned either in the utmost compression region or in both the compression and tension regions. The experimental results revealed that the FGRC beams exhibited strength and ductility comparable to those of pure UHPFRC beams but at a significantly reduced cost. When UHPFRC layers constituted 66.7 % of beam thickness, the FGRC beams were capable of carrying 97.4 % of the load sustained by a full UHPFRC beam, while for UHPFRC layers constituted 40 % of beam thickness the FGRC beam carried 77.5 % of that of a full UHPFRC beam. Increasing ρl% from 1.38 % to 5.68 % in the tested specimens led to a considerable enhancement in the flexural capacity. The sectional analysis conducted in accordance with the recommendations of AFGC-2013, JSCE-2008, and KCI-2012 showed precise predictions of the flexural strength in both UHPFRC and FGRC beams, while the flexural strength calculated using the equations adopted in the studied codes gave conservative estimations. The proposed numerical model displayed a high level of agreement with the experimental findings of the studied FGRC beams.