Study On Concrete-Filled Steel Tube Rock-Socketed Pile Steel-Concret Interface Characters Under Horizon Cyclic Load

Concrete-filled steel tube rock-socketed pile as a type of deep foundation is constantly used in deepwater wharf with shallow overburden and the construction of crossing-river bridges.In practical engineering,piles are exposed not only to the dead weight,but also the cyclic horizon loading induced by winds,waves,or ship impact load.Steel-concrete interface cyclic strength weakening directly affects security and stability when the normal use of deep-water wharf and other important engineering under cyclic horizon loading.Based on the national natural science fund project Study on steel-concrete interface strength weakening mechanism and long-term work behavior of concrete-filed steel tube embedded in concrete under cyclic loading,load-bearing behavior of concrete filled steel tube and the properties of steel and concrete interface working characteristies under horizontal cyclic loading are studied through large scale model test.In this paper,the main research work and achievements are as follows:Firstly,the rock-socketed pile with steel casing of Guo Yuan port is taken as prototype of model piles which are divided into three groups.The study shows that,the deformation development law of the pile meets three stages under different cyclic loading,which are linear growth stage,slow growth stage and sharp increase stage.each stage accumulation cycle times accounted for the proportion of the fatigue life roughly 8.5%,83%,8.5%.Secondly,the influence factors of steel and concrete interface bond weakening is discussed.The greater the force of the interface is subjected the more obvious influence by cyclic number.And greater cyclic loading,more serious stress concentration will accelerate the attenuation of the interface.Thirdly,strain variation regularity of the steel-concrete interface can be got through placing strain tablets at the same cross section of the pile on steel pipe,concrete test block and the steel.The results showed that,the degree of stress and strain redistribution of steel-concrete interface will be greater and failure occurs earlier with the increase of cyclic amplitude.The degree of steel-concrete interface stress redistribution increased gradually and tends to be stable finally with the increase of cycling times.Fourthly,the steel-concrete interface cohesive force and the damage process are analyzed based on hysteretic characteristics of concrete-filed steel pile and strain variation regularity of the interface.The cohesive force of steel-concrete interface is composited with three parts which are chemical bonding force,frictional force,and dynamic friction.the damage process can be divided into micro slip stage micro cracks(elastic stage),sliding stage,micro cracks development stage and residual stage.Fifthly,cumulative damage variable of concrete-filled steel tube rock-socketed pile is defined based on stiffness degradation.The change process of the concrete-filled steel tube rock-socketed pile stiffness cumulative damage showed S type of three stage variation regularity under different cyclic load.