Experimental Study On The Minimum Stirrup Ratio Of Reinforced Concrete Simply Supported Beams

The minimum stirrup ratio is one of the important structural measures for reinforced concrete beam members.China’s current code for design of concrete structures GB 50010（referred to as China’s code）follows the concept of the design code of the 1980s.By substitutingV_{mi n}（28）0.1f _cbh₀?1.0f _tbh₀（the minimum shear design value of the beam with the minimum stirrup consumption）into the shear bearing capacity calculation formula to get the minimum stirrup ratio calculation formula of the beam with web reinforcement.At present,the research on the performance of minimum stirrup ratio in shear failure of beams with web reinforcement at home and abroad shows that the concept of minimum stirrup comes from the shear safety reserve of beams.There is a significant size effect in the shear capacity of beams without web reinforcement,and a certain number of stirrups can reduce the size effect.In fact,the minimum stirrup ratio of the recently revised ACI 318-19 code considers the safety of the shear capacity of large-size beams.Moreover,the shear failure of the beam is brittle failure,especially when the shear span ratio is large.The minimum stirrup ratio can transform the cable-stayed failure to the shear compression failure,and improve the brittle property of the shear failure.For the reasonable value of the minimum stirrup ratio,researchers at home and abroad have carried out more extensive research.According to the code formula of our country,the minimum shear capacity of beams with web reinforcement should not be less thanf_t bh₀,which largely depends on the shear capacity of beams without web reinforcement.However,the calculation formula of shear bearing capacity in the existing concrete structure design code is not based on the analysis of shear failure mechanism,but on the empirical formula based on the experimental data analysis.The shear mechanism is not very clear,and the prediction of shear bearing capacity varies greatly in different design codes.The existing research shows that the shear capacity of beams without web reinforcement is not safe enough in the code formula of our country,which leads to the doubt whether the beams with the least stirrups can meet the requirement off_t bh₀.Therefore,in order to further study the shear performance of reinforced concrete beams with minimum stirrup ratio,this paper completed the shear performance test of36 simply supported reinforced concrete beams（12 beams without web reinforcement and 24 beams with web reinforcement）under the action of concentrated load,and took the stirrup ratio（0,minimum stirrup ratio,construction of stirrup requirements）,shear span ratio（2.2,2.6,3.0,3.4）and concrete strength（C25,C45,C65）as the experimental variables.Such as failure mode,crack development,diagonal crack load,main diagonal crack load,shear capacity and mid span deflection,are compared.At the same time,the influence of a small amount of stirrups on the shear performance of beams is discussed,and the calculation formulas of the minimum stirrup ratio of GB50010-2010,ACI 318-19,CSA A23.3-14 and EC 2-02 are compared.On this basis,the rationality of the minimum stirrup ratio in GB 50010-2010 is analyzed.Combined with the test results of this paper and the shear failure test data of rectangular section beams without web reinforcement and beams with web reinforcement in the range of minimum stirrup ratio collected from the relevant literature at home and abroad under the action of concentrated load and uniform load,the calculation formula of shear in GB 50010 is evaluated to see whether for beams without web reinforcement and beams with minimum stirrups have enough safety.Based on the statistical analysis of the existing shear test data,the calculation formula of shear capacity of beams with web reinforcement and a small amount of stirrups is proposed.