Study On Shear Capacity And Failure Mode Of High Strength Reinforced Concrete Beams

In the 1980s,Japan began to study the systematic application of the reinforced concrete high-rise building structure with the use of lightweight high-strength concrete and high-strength reinforcement,and applied the research results to the actual project.For more than 30 years,other countries have also carried out research on the application of high-strength materials.Combined with the two revisions of the code for design of concrete structures(gbj 50010)in 2002 and 2010,China has also carried out the application research of high-strength steel bars,and included 400MPa and 500MPa highstrength steel bars in the two revisions,in order to comply with the development trend.However,up to now,the application of high-strength reinforcement in our country is not widespread,one of the important reasons is that the design theory and method of concrete structure with high-strength materials are not perfect,so it is necessary to further strengthen the research on the mechanical properties of reinforced concrete structure with high-strength materials.The mechanical properties of high-strength steel bars and high-strength concrete are different from those of ordinary materials,which leads to the mechanical properties of these high-strength reinforced concrete members and structures have their own characteristics.With the increase of the experimental and theoretical research on the mechanical properties of reinforced concrete beams using this kind of high-strength materials,the current design codes of concrete structures in various countries mostly consider the characteristics of high-strength materials on the basis of the original design methods,and modify to a certain extent to get the current design methods suitable for the application of high-strength materials.There is no problem in this way of thinking.The problem is that at present,there is not much accumulation of relevant research results in China,and most of the experiments are tracking and confirmatory,without forming systematic theories and design methods.If foreign design theories and methods are introduced,whether these theories and methods meet the requirements of China’s design specifications and engineering practical application needs to be further improved Step by step.The work of this paper is divided into two parts.First of all,based on the collection and arrangement of the test data of reinforced concrete beams without web reinforcement and with web reinforcement using high-strength materials at home and abroad,the main influencing factors and rules of the shear performance of high-strength concrete beams without web reinforcement and high-strength concrete beams with web reinforcement are studied,and the shear design theory and method of ordinary strength concrete and reinforcement are extended to mining The feasibility of shear design of reinforced concrete beams with high strength materials.Secondly,the index of using the ratio of relative bending moment,that is,the ratio of bending capacity and bending moment capacity corresponding to the ultimate shear at the time of failure,is proposed to describe the bearing capacity of the beam with shear failure.On the basis of the existing research,further research adopts the The concept of "shear Valley is used to verify the original conditions of bending failure and shear failure of beams without web reinforcement and beams with web reinforcement.Therefore,for any structural member,the change rule of relative moment ratio with shear span ratio and longitudinal reinforcement ratio can be obtained;the expression of critical shear span ratio gives the boundary of shear compression failure and cable-stayed failure;the combination of analytical model and expression of critical shear span ratio can more accurately identify the bending failure,shear compression failure or cable-stayed failure of the member under a certain shear span ratio and longitudinal reinforcement ratio.The main work of this paper is as follows.①The shear failure test data of 238 high-strength concrete beams without web reinforcement and 139 high-strength concrete beams with high-strength web reinforcement were collected,including the effective height of the test beam,shear span ratio,concrete strength,longitudinal reinforcement ratio,stirrup ratio,maximum aggregate size.②Using statistical analysis method to evaluate ACI318-14,GB50010-2010,EC2,including B method,A method of Japanese Design Guidelines to predict the shear capacity of beam with high-strength material.③The influences of such parameters as concrete compressive strength,shear span ratio,effective height,longitudinal reinforcement ratio and stirrup restraint stress on the shear capacity of high material beams are investigated,including the correlation between these parameters.④Based on the discussion of(3),nonlinear regression is used to modify the concrete and stirrup contribution of high-strength material beam.⑤The prediction model of the failure mode of the beams without web reinforcement is established.As long as the ρ and a/d is given,the failure mode of the beams without web reinforcement can be predicted.On the other hands,the beams without web reinforcement with specific failure mode can be designed,and the accuracy of the prediction model can be verified by using the existing database of high-strength concrete beams without web reinforcement.⑥The relationship between the angle between the concrete compression bar and the longitudinal reinforcement and the stirrup reinforcement ratio,stirrup strength,concrete strength,shear span ratio is obtained by regression,so that the prediction model of the failure mode of the non web reinforcement beam is extended to the beam with web reinforcement,and the accuracy of the prediction model is verified by the existing double high beam database.