| Abstract: |
An experimental investigation on the shear behaviour of reinforced concrete beams with and without web reinforcement made of HSC is presented. The experimental study carried out included testing thirty-six reinforced concrete beams to investigate the factors affecting the shear behaviour of reinforced HSC beams. The major test variables were: the concrete compressive strength (fcu) ranged from 25, 60 to 90 MPa; the shear span to depth ratio (a/d) changed from 2 to 3; the longitudinal main steel reinforcement ratio (?) changed from 2.26 to 4.02 % and for beams with web reinforcement the web reinforcement ratio (?v) varied from 0.0, 0.57 to 1.01 % in the form of vertical stirrups.Two equations were proposed for predicting the cracking and ultimate shear strengths depending on the major test variables. A detailed comparison was made between the experimental values of the cracking and the ultimate shear strengths obtained from this study and from the literature and the estimated values using the proposed equations in this study and the other predictive equations proposed by other investigators.6.2 Conclusions and RecommendationsFindings from the experimental study and the analysis of such test results and variables brought out a number of interesting points. Although most of theses findings are written in their proper location through the text, they will be summarized here for reference:1. The higher the compressive strength, the higher is the initial crack load, and also, it is noticed that, the number of cracks and their widths decreases, this is due to the increase in tensile strength.2. The cracking and the ultimate loads increase as shear span to depth ratio (a/d) decreases, this is because cracks form in the shear regions at places of high moments which are towards the applied concentrated loads, as shear span to depth ratio (a/d) decreases this distance also decreases, and the slope of the cracks become more steep.3. As the longitudinal steel reinforcement ratio (?) increases, the penetration of the flexural crack decreases. Also beams with low longitudinal steel reinforcement ratio (?) have large deflection since their inertia is relatively low and hence will have wide large cracks in contrast to short narrow cracks in beams with high longitudinal steel reinforcement ratio (?).4. As the web reinforcement ratio increases, the shear resistance of the beams increases, and also, the beams became more ductile and hence, failures were less sudden.5. The slopes of the load-midspan deflection curves increase slightly with increase of the web reinforcement ratio (?v). Also, it is found that, failure and cracking loads increase with increase of the web reinforcement (?v).6. The increase in shear span to depth ratio (a/d), decreases the ultimate shear loads. The increase of web reinforcement decreases the values of the strain, this is because stirrups tend to close the cracks.7. The values of the measured longitudinal strains at the shear span for all beams increased significantly after the formation of the diagonal crack however, strain values were more or less small at the first stages of loading before the first diagonal crack was formed. And also, it is concluded that, the increase of web reinforcement, decreases the longitudinal strains at the shear span, and the increase of concrete compressive strength, decreases the longitudinal strain values at the shear span.8. An equation has been proposed for predicting the cracking shear strength of reinforced concrete beams based on the multiple regression analysis for the test data of 201 reinforced concrete beams with and without stirrups failed in shear obtained from this study and from other previous investigators including the major factors affecting the cracking shear strength as follows:vcr = 2.88 ( fc? ? )0.3 ( d/a )0.6 (mm-N)9. A second equation has been proposed for predicting the ultimate shear strength of reinforced concrete beams based on the multiple regression analysis for the test data of 271 reinforced concrete beams with and without stirrups failed in shear obtained from this study and from other previous investigators including the major factors affecting the ultimate shear strength as follows:vu = 2.88 d/a + 1.1 (mm-N)6.3 Recommendations for Future WorkThe following recommendations may be pointed out as suggestions for future work:1. Studying the shear strength in continuous reinforced HSC beams.2. Studying the fatigue shear strength for reinforced HSC beams.3. Studying the shear strength for reinforced UHSC beams.
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