Experimental Study And Finite Element Analysis On Steel Fiber Reinforced High Strength Concrete Three-Pile Caps

Recently, pile foundation has been widely applied owing to its high bearing capacity, small and uniform settlement and good anti-seismic performance, in which the caps of pile form a connecting link between the upper structure and the down pile so that it is the crucial bearing component of pile foundation. It is very important to improve the mechanical properties of caps. The steel fiber reinforced high strength concrete can improve the crack resistance, shear resistance, earthquake resistance and the durability of pile caps. Also, it can reduce the thickness of pile caps. Therefore the application of SFHSC provides a new way to meet the request of high-rise and high-rise building to pile caps. The mechanical properties and transfer model of SFHSC three-pile caps were discussed by experimental research and theoretical analysis in this paper, and the main contents are as follows:(1) Based on the experimental study on 6 specimens of SFHSC three-pile caps with the ratio of the model to the real of 1:5, the effects of two variable parameters including the thickness of the cap and the volume fraction of steel fiber were studied. The developing of cracks and failure of caps were described. The test results indicate that the destruction of three-pile cap belongs to shear or punching failure, which is different from that of the general bending member.(2) The influence factors of bearing capacity of SFHSC three-pile caps were analyzed based on the test results and study at home and abroad. It can be achieved that such factors as the effective thickness of three-pile caps, concrete strength, the shear-span ratio, the volume fraction of steel fiber and reinforcement quantity and reinforcement approach of three-pile caps have remarkable effects on the bearing capacity of SFHSC three-pile caps. Also the type of steel fiber is an important influence factor of bearing capacity of three-pile caps.(3) Based on the experiments, the stress of longitudinal reinforcement and the strain of concrete were analyzed. It indicates that the stress of reinforcement along the length has little change and the reinforcement is like a tension rod. The mechanical behavior of SFHSC three-pile caps can be imitated by the space truss model. The strain of concrete no longer meets the plane-section assumption, the mechanical properties of three-pile caps meets the space truss model.(4) The finite element analysis models of three-pile caps were established to discuss the transfer model of three-pile caps. The results suggested that the transfer model of three-pile caps meets space truss model. The failure of caps is due to shear failure or splitting tensile failure of slanting compressive member of steel fiber reinforced high strength concrete formed within the range of linking line between column and corner pile.