Experimental Study On Mechanical Behavior Of Steel Fiber Reinforced High Strength Concrete Five-pile Caps

Five-pile caps is a special type of pile caps,which has good mechanical performance and high bearing capacity.A large number of structural tests and finite element analysis have been carried out on ordinary strength concrete and steel fiber reinforced concrete caps at home and abroad,but the research on steel fiber reinforced high strength concrete five-pile caps has not been carried out yet.Therefore,it is of great theoretical significance and practical value to explore the performance of steel fiber reinforced high strength concrete five-pile caps.In this paper,the mechanical behavior,failure mode and bearing capacity calculation method of steel fiber reinforced high strength concrete five-pile caps are studied through model test and theoretical analysis.The main research contents are as follows:(1)Through the static load test of 10 steel fiber reinforced high strength concrete five-pile caps with a model ratio of 1:5,the occurrence,development,distribution and failure mode of the pile caps’ cracks under various loads were observed.The test shows that the failure mode of steel fiber reinforced high strength concrete five-pile caps is punching shear failure.The reaction force of the middle pile is obviously higher than that of the corner pile.The thickness of pile caps affects the ratio of reaction force of each pile.As the thickness of the cap decreases,the reaction ratio gradually increases.(2)The load-deflection curve of pile caps and the distribution curve of concrete strain along the height of pile caps section were analyzed,load-reinforcement strain curve,as well as the influence of different test parameters such as effective thickness of pile caps,the volume fraction of steel fiber and concrete strength on the mechanical performance of steel fiber reinforced high strength concrete five-pile caps.The results show that the mechanical characteristics of steel fiber reinforced high strength concrete five-pile caps do not conform to the plane section assumption,and the bearing capacity of the pile caps was mainly affected by the effective thickness of the cap and the volume fraction of steel fiber.(3)By studying the crack development,deflection,concrete strain and reinforcement strain characteristics of the pile caps,the stress mechanism of the steel fiber high strength concrete five-pile caps is clarified.The force transmission mode of strut fiber reinforced high strength concrete five-pile caps is that the straight compression strut and the diagonal compression strut share the compressive stress,and the tie bears the tensile stress,which conforms to the space strut-and-tie model.(4)According to the design specifications or other existing bearing capacity calculation formulas of five-pile caps,the test datas in this paper are used for comparative analysis.The results show that the calculated bearing capacity of the five-pile caps based on the space strut-and-tie theory is in good agreement with the test value.The calculation method of the bearing capacity of the five-pile caps based on the space strut-and-tie theory can provide a reference for the application of the five-pile caps.