Behaviour Of Big Size Reinforced Concrete Beams For Shear In Compliance With Compressive Force Path Method

In field of the basic theory for concrete structures,the research on shear capacity of reinforced concrete beam has always been a key research issue,which has been extensively and deeply studied by scholars in various countries.However,in the concrete structure codes of most countries including China,the calculation formula of shear capacity is still a semi-empirical and semi-theoretical formula with a certain reliability based on the statistical analysis of experimental results.Owing to the complexity of the shear mechanism and various influencing factors of shear capacity,the mechanism of shear failure still lacks a unified calculation model and shear theoretical system.Although the reliability of the shear calculation formula in our codes has been improved,the amount of stirrups has been increased than before,and the study on large-size components is also not sufficient.Therefore,it is of important theoretical significance and engineering economy to investigate the shear capacity and reasonable calculation model of shear capacity for large size reinforced concrete beams.Based on the above research background,this paper studied the compressive force path method proposed by Kotsovos,a Greek scholar.The underlying point of this theory is that,for a reinforced concrete beam in its ultimate state,the highest stresses sections are located in the compressive force path.These sections will become the dangerous regions of the beam.If we can increase the stirrup ratio in these specific sections,the shear capacity of the reinforced concrete beam can be increased evidently.According to this method,three groups of large-size reinforced concrete beam members with different shear span ratios were designed.Each group has three specimens,respectively designed by the compressive force path method and Chinese national standard method,in addition,we also designed a compressive force path beam adopting the construction reinforcement suggested by Chinese code,thus to compare each other.Such mechanical properties are obtained by the tests as the cracking process,failure phenomenon,ultimate load,load deflection curves and load strain curves of the beams.Through the experimental research on the shear mechanism of large reinforced concrete beams by compressive force path method,the practicability of this theory in large-size components is verified.The results show that,the shear capacity of the reinforced concretecomponents is mainly affected by the stresses on the compressive force path,the reinforcement calculated with the compressive force path method will not only maintain the shear capacity,but also greatly reduce the amount of stirrup.After analyzing the shortcomings of methods in our code and the applicability of the compressive force path theory,a more reasonable shear failure mechanism and component design method is proposed herein,which can provide references for the relevant standards of China.