Numerical Simulation Study Of Load Transfer And Steel-concret Interface Characters Of Concrete-filled Steel Tube Piles Under Horizontal Cyclic Load

Three Gorges reservation of water has been greatly improved reservoir area channel.But there are some deep water construction problem in wharf construction.Concrete-filled steel tube rock-socketed pile as a type of deep foundation is constantly used in deep water wharf with shallow overburden and the construction of crossing-river bridges.Use steel casing as construction protection measures.Steel pipe and pile core concrete have common stress properties in later use cycle.With concrete-filled steel tube rock-socketde pile under long-term effects of various complex loads,steel-concrete interface fall off and slip.And it also lead to bearing capacity decline or deform.It will directly effect the bearer status and structural safety of concrete-filled steel tube rock-socketde pile..Finding out the load transfer mechanism and strength weakening mechanism of steel-concrete interface,which is the key to evaluate the bearing behavior of concrete-filled steel tube rock-socketde pile.This paper combine \combined national nature science fund projects “strength weakening mechanism and long-term performance of steel-concrete interface of strength weakening mechanism of concrete piles under cyclic loading”.The properties of the steel-concrete interface under cyclic loading and the bearing characteristics of the concrete-filled steel tubular piles are systematically studied.(1)The study of the law of load transfer through the steel-concrete interface shows that adhesion at the interface of concrete-filled steel tubes is controlled by chemical bonding force and mechanical bite force.Cement properties and steel pipe surface roughness have a decisive effect on the ultimate bond strength.Detackling and slippage in the upper part of the interface is earlier than the lower part.The bonding force exerts a sequential order and reveals the load transfer mechanism of the steel crucible interface.(2)With the nonlinear increase of the shear stress at the interface of the steel concrete structure,the peak load decreases gradually,and finally tends to the residual stability value,the interfacial strength is weakened.Based on the interfacial bond slip model,a nonlinear spring element constitutive model is established by piecewise interpolation,and the numerical method for the bond slip of the steel concrete interface is established.(3)Based on the calculation models of the steel concrete interface,the numerical calculation model of the concrete filled steel tube rock-socketed pile is established considering the strength weakening of the steel concrete interface and the nonlinear characteristics of the steel pipe,concrete and so on under cyclic loading.(4)Based on the steel tube concrete piles calculation model,the stress-strain behavior of steel tube and concrete,piles moment,pile body deformation and failure mode are analyzed.The research shows that under the lateral load,the fatigue cumulative of the steel tube contrete pile on the compression side is easy.Under the influence of subgrade reaction,foundation surface and vary-sectionpile are the weak interface of concrete filled steel tube.The failure of pile foundation is mainly caused by the weakening of the foundation on the pile foundation under the long-term load,which leads to the debonding of the steel concrete structure interface,the steel pipe of local bulge and yield and the tensile fracture of the concrete,which leads to the general demoitionl of pile foundation.