Experimental Study On Punching Shear Behavior Of Steel Fiber Reinforced High-Strength Concrete Four-Pile Caps

Reinforced concrete four-pile caps have been widely used in hydraulic structures and offshore drilling platforms because of simple structure,easy construction and excellent seismic performance.A large amount of research on the punching shear behavior of reinforced ordinarystrength concrete or steel fiber reinforced concrete four-pile caps were carried out by domestic and foreign scholars,however,experimental research on the punching shear behavior of steel fiber reinforced high-strength concrete(SFRHSC)four-pile caps has not yet been carried out.In this paper,the punching shear behavior,the influencing factors of bearing capacity,and a calculation method for punching shear bearing capacity of SFRHSC four-pile caps were studied hereby incorporated experimental study and theoretical analysis.The main contents are as follows:(1)According to the experimental investigation on punching shear behavior of 9 SFRHSC four-pile caps,the occurrence and development of cracks and failure mode were studied.Test results show that the main failure mode of SFRHSC four-pile caps is punching shear failure.(2)The characteristics of the load-deflection curve,the distribution curve of concrete strain along the height of the section,and the load-steel strain curve of SFRHSC four-pile caps were studied.Test results show that the concrete strain of SFRHSC four-pile caps no longer conforms to the plane section assumption;the failure process of specimens change from bending,shearing,to punching shear,and eventually punching shear failure occurs.(3)The effects of the thickness,steel fiber volume fraction,steel ratio,and bar arrangement on the punching shear bearing capacity were analyzed.The results show that the punching shear bearing capacity of pile caps is significantly influenced by the thickness and the steel fiber volume fraction;with the increment of the steel ratio,the bearing capacity is effectively improved;the bearing capacity of the pile caps is improved certainly by using bunched or diagonal bunched bar arrangement.(4)The punching shear failure mechanism and bearing capacity calculation method of SFRHSC four-pile caps were studied.The results indicate that the mechanical mechanism of SFRHSC four-pile caps conforms to the space strut-and-tie model;the specimens fail as result of diagonal splitting of strut,rather than the crushing of strut or the yielding of tie.On this basis,a calculation method for punching shear bearing capacity of SFRHSC four-pile caps was proposed based on the space strut-and-tie model.