Effect of longitudinal reinforcement strength on shear strength of reinforced concrete beams and slabs

Pathuri, Jayender Reddy
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This thesis evaluates the shear strength of beams with high-strength longitudinal reinforcement. The focus of the research is on beams with longitudinal reinforcement yield strengths (fy) of 100 and 120ksi. A parametric study was performed using the implementation of Modified Compression Field Theory in the analysis program RESPONSE 2000. The parametric study consisted of 468 simulations evaluating the influence of shear span-to-depth (a/d) ratio, concrete compressive strength (f'c), presence of minimum shear reinforcement, and longitudinal reinforcement ratio (which is dependent on the yield strength of the reinforcement), on the shear strength of beams with effective depths ranging between 22.5 and 45.5 in. The effect of yield strength on the shear strength of beams was also evaluated using a database with results from 425 shear tests of beams with nominal longitudinal reinforcement strengths ranging between 40 and 120 ksi. Simulation and experimental results were used to evaluate design provisions for shear in the 2014 AASHTO LRFD and ACI 318-14 Building codes. It was found that design provisions in the 2014 AASHTO code, which account for the effect of neutral axis depth on shear strength, provided adequate estimates of normalized shear strength for the range of concrete compressive and reinforcement yield strengths studied. The simplified provisions in the ACI 318-14 Building Code provided unconservative estimates of shear strength, with the level of unconservatism increasing with concrete compressive strength and reinforcement yield strength. The presence of minimum shear reinforcement specified in the ACI 318-14 Building Code improved the estimates for beams with normal strength concrete, but the level of unconservatism increased with concrete compressive strength.

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Civil and Environmental Engineering