Experimental study on the flexural response of UHPC beams encased high-strength section steel

In consideration of the positive synergetic between H-shaped steel and concrete in SRC structures, this paper investigates the flexural behavior of high-strength steel reinforced UHPC (HSSRUHPC) beams. Six HSSRUHPC beams with different H-shaped steel ratios (5.5 %, 6.8 % and 8.7 %), steel configurations (concentric and eccentric placement) and steel fiber volume fractions (1 %, 2 % and 3 %) were tested under two-point symmetrical loading. The structural performance was examined involving failure pattern, load versus deflection response, load-strain behavior, and load carrying capacity. Experimental work indicated that the failure mode for all specimens occurred via the typical bending failure of the under-reinforced beams, although the failure still unfolded slightly fragility with an abrupt drop in post-peak bearing value. With the addition of steel fiber increasing, the sudden unloading at peak load could be degraded due to the superb “bridging” effect, which also inhibits the elongation of cracks and enhances the bearing capacity of specimens. The test results also signified that the initial stiffness and flexural capacity of HSSRUHPC beams are improved linearly with the H-shape steel ratios, and shifting the steel section downward from centroid is instrumental in discharging more concrete to resist compressive strength, whereas it exerts an adverse effect on post-peak bearing stability. Finally, a theoretical analysis methodology was proposed to reckon the ultimate moment of HSSRUHPC beams, which incorporated the momentous contribution of UHPC tensile force based on the plane section hypothesis. The test data along with additional test results sorted from other literature were used for comparing the distinction between theoretical predictions and test values. This method exhibiting good correlation is thus illustrated to estimate the bending capacity of HSSRUHPC beams with high accuracy, which provides a reference for the design of SRC members reinforced by high-strength materials.