Shear Models Of Reinforced Concrete Simply Supported Beams With Web Reinforcement

Scientists have been doing researches on shear behavior of elements for many years, and eager to find a set of relative complete and correct models for shear analysis. But because of complexity of shear behavior, most shear formulas in current codes are empirical or semi-empirical, rather than derived from clarify physical models, which limits their application scope. First of all, three representative shear design methods in current codes and several principal shear analysis models are introduced in this article; then, on the basis of shear database of reinforced concrete beams with web reinforcement, shear design methods are checked; By this, shear models of reinforced concrete beams with web reinforcement are analyzed and assessed.The details of this work and corresponding main results are as follows:①Analyses of 351 simply supported beams with web reinforcement subjected to concentrated loads reveal following rules.1)For 149 elements of which l_n/ h≥5, V /bd increases when shear span ratio, longitudinal steel content, and vertical reinforcement content increase, but decreases when effective depth increase.2)For 202 elements of l_n/ h < 5, when vertical reinforcement pvfy is smaller than 3.0, V /bd tend to increase with the concrete strength increasing; but when vertical reinforcement pvfy is bigger than 3.0, the tendency is not as obvious as the former. Except that vertical reinforcement pvfy of some elements is between 2.0 and 3.0, V /bd of other elements decreases with shear span ratio increasing, and increases with longitudinal steel content increasing. In addition, V /bd tend to increase with the vertical reinforcement content increasing, some points of which the concrete cubic strengths are between 50 and 80 MPa excepted.②Comparison of using three codes to predict shear capacity of 351 simply supported beams comes to following conclusions:1)For 149 elements of which l_n/ h≥5, the average ratio of shear capacity predicted by CSA94 general method, GB02 method, and ACI05 method to that of experiment is respectively 0.93, 0.87, 0.65; meanwhile, coefficients of variation are respectively 0.28, 0.27, 0.29. By contrast, method based MCFT (Modified Compression Field Theory) (CSA general method) is more precise than semi-empirical methods (GB02, ACI05 method). 2)For 10 elements of which 4 < l_n/ h < 5且a / d>2, the average ratio of shear capacity predicted by CSA94 general method, GB02 method, ACI05 method to that of experiment is respectively 1.0, 0.84, 0.69; meanwhile, coefficients of variation are respectively 0.15, 0.15, 0.16.3)For 6 elements of which 4 < l_n/ h < 5且a / d≤2, the average ratio of shear capacity predicted by CSA94 general method, GB02 method, and ACI05 method to that of experiment is respectively 0.81, 0.64, 0.77; meanwhile, coefficients of variation are respectively 0.10, 0.19, 0.09.4)For 155 elements of which 2≤l_n/ h≤4, the average ratio of shear capacity predicted by CSA94 general method, GB02 method, and ACI05 method of Strut-and-Tie Model to that of experiment is respectively 0.62, 0.71, 0.78; meanwhile, coefficients of variation are respectively 0.30, 0.20, 0.43. For elements of which the concrete cubic strength is between 50 and 80, vertical reinforcement pvfy is smaller than 2.0, and shear span ratio a /d is smaller than 1.5, shear capacity predicted by GB02 method is conservative (average safety factor is 2); safety factor of using CSA94 general method is much bigger ( average value is 3.0). So for these elements, method based on MCFT (CSA94 general method) and empirical method(GB02 method) are less effective than method of Strut-and-Tie Model.5)For elements of which l_n/ h≤2, the average ratio of shear capacity predicted by CSA94 method of Strut-and-Tie Model, GB02 method, ACI05 method of Strut-and-Tie Model, and Finite Element Method VT2 to that of experiment is respectively 0.41, 0.68, 0.65, 0.70; meanwhile, coefficients of variation are respectively 0.15, 0.15, 0.27,0.30. None of these methods are satisfying.