SIFATULLAH BAHIJ2022-05-182022-05-185938https://drepo.sdl.edu.sa/handle/20.500.14154/1388Recently, attempts are being made for utilizing a new concrete material, named ultra-high performance concrete (UHPC), in reinforced as well as in pre-stressed concrete beams. UHPC consisting of ultra-fine materials and steel fibers without coarse aggregate possesses very high compressive and tensile strengths, toughness, ductility, stiffness, and low permeability. The study of structural behavior of UHPC beams considering the simultaneous effects of key parameters is a great significance for optimum design of the beams prepared using UHPC and high-strength steel bars. This research work was conducted to investigate the effects of key structural parameters on the shear behavior of non-prestressed ultra-high performance concrete (UHPC) beams passively reinforced with high strength steel bars (ASTM A722/A722M). The parameters studied were shear span to effective depth, a/d ratio, volume fraction of steel fibers, Vf, longitudinal reinforcement ratio, ρ, and stirrups spacing, s. Ten reinforced UHPC beam specimens with cross sectional dimensions of 150 mm × 225 mm were prepared and quasistatically loaded to failure on a simple span length of 1.75 m, under a four-point loading configuration. The data pertaining to shear behavior (such as modes of failure, ultimate shear strength, mid-span deflection, strains in steel bars and concrete, etc.) were recorded for analysis. Nonlinear 3-D finite element Modeling, using the concrete damage plasticity (CDP) model and material properties obtained from uniaxial compressive and tensile laboratory tests, was conducted to simulate UHPC beams using a commercial finite element software package ABAQUS 6.13. The developed model was validated with experimental results. Thereafter, a parametric study was conducted to further improve the understanding of shear behavior of UHPC beams and evaluate the contribution of the various levels of the variable parameters that were not included in the experimental program. In addition, statistical analysis was conducted to quantify the real level of significance of the four key factors. The test response was the shear capacity of the beams, Vu. Using the experimental data generated under the present work, an attempt was made to best-fit an equation to predict shear capacity of UHPC beams in terms of a/d ratio, Vf, stirrups spacing, and p. The results of the experimental study indicated that shear capacity and mid-span deflection increased with the increase in volume fraction of steel fibers, Vf, percentage of longitudinal reinforcement, ρ, and with the decrease in stirrups spacing and a/d ratio. Overall, finite element model was in good correlation with experimental results; therefore, it can be used in design and analysis. Statistical analysis of experimental data indicated that a/d, Vf, and stirrups spacing have significant effect on the shear capacity and failure behavior of beams, while the effects of ρ is quite insignificant. The experimental values of Vu and the values of Vu predicted using proposed shear capacity equation are validated and good agreement between the results was obtained. This indicates that the proposed equation can be used for shear design with a fair degree of accuracy for UHPC with compressive strength of around 150 MPa and in presence of shear stirrups.enThesis