Study On Shear Behavior Of High Strength Reinforced Concrete Beams Based On Modified Compression Field Theory

In the basic theory of concrete components,the shear mechanism analysis of flexural members is a very complicated problem.With the growing maturity and popularization of high-strength steel and high-strength concrete,the shear behavior of high-strength reinforced concrete beams has gradually become the focus of researches.And a large number of empirical formulas have been developed,but the accuracy is slightly lacking.Otherwis,the study on shear behavior of reinforced concrete beams with high strength steel fibers is relatively few.And most of the known research results are based on experimental data.They are the semi empirical and half theoretical formulas obtained by adding fiber influence coefficient to the relevant formulas of high-strength reinforced concrete beams.And the applicability of those formulas needs further verification.The shear behavior of high strength reinforced concrete beams and steel fiber reinforced high strength reinforced concrete beams in this paper is studied and discussed by using the modified compression field theory as the shear model.The formula for calculating the related shear capacity is derived.The main conclusions are as follows:(1)It is known from the evolution process of the modified pressure field theory and the content of its hypothesis that its advantage is to consider the shear contribution of the tensile stress after the cracking of the concrete,and to predict the shear bearing capacity of the beam and the description of the whole process of load deformation from crack to shear failure of members.,combining with conditions like stress-strain equilibrium?local stress checking conditions at cracks and so on.(2)Through the analysis of the shear stress characteristics and the existing experimental results of the high strength reinforced concrete beams,it is found that the shear force is jointly undertaken by the concrete in the upper compression zone and the lower tensile zone,and a formula of the shear bearing capacity of the high strength reinforced concrete beams is derived.(3)Because of the high tensile strength of steel fiber,the addition of steel fiber can effectively improve the shear ability of the stirrup and the effect of the dowel action.Considering the influence of concrete in the compression zonedowel action,the dowel action and the fiber stress on the shear performance of beams,a formula based on the modified compression field theory for calculating the bearing capacity ofsteel fiber reinforced high-strength reinforced concrete beams can be derived.(4)By adhitbitting the shear resistance's contribution coefficient of steel fiber and the dowel action,and the unified calculation formula of the bearing capacity of concrete beams is given.(5)The calculation formula of the bearing capacity is verified by the experimental data of our research group,and the results are in good agreement.At the same time,the experimental data of relevant literature are used to compare the shear model in this paper and other shear models.The results show that the precision of the shear model is high,and the reference value is more practical.