Experimental Study On Bending Resistance Of U-shaped Steel Sheet Pile Under Repeated Loading And Unloading

U-shaped steel sheet pile is a kind of complex section structure with special locks on both sides.It has been widely used in support engineering because of its high construction efficiency,good self-healing effect,green environmental protection and other advantages.Due to the special locking connection mode of steel sheet pile,the development of the bending strength of steel sheet pile under bending has a strong relationship with the change process of the contact occlusion between the locks.And it makes the research of the bending performance of steel sheet pile have some complexity and uncertainty.when the locks between the piles are smoothly connected,each steel sheet pile participates in bending resistance alone;when there is no relative slippage between the locks of the piles,the steel sheet piles are tightly combined to form a whole to participate in bending resistance;In practice,there is a certain amount of slip between the locking openings of the steel sheet pile wall,and the flexural strength is between the single pile and the ideal pile wall,and it changes with the deformation of the specimen.At present,there are few experimental studies of mechanism on the bending resistance of U-shaped steel sheet piles at home and abroad.Therefore,by setting suitable test equipment,the paper conducts laboratory test on steel sheet pile,analyzes its flexural performance under bending action,and discusses the formation mechanism of its flexural mechanical properties.The main research contents are as follows:1.The bending tests of steel sheet pile composite structure under repeated loading and unloading were carried out,and the deflection of pile body,the slip of interpile lock and the positive bending strain of cross section were tested.2.Combined with the measured data,the variation law of deformation characteristics such as slip and deflection with the load is analyzed.It is found that in the elastic loading stage,the occlusion of the locking mouth of the steel sheet pile is gradually compact,and the bending stiffness of the steel sheet pile is gradually enhanced.In the unloading stage,the bending deformation decreases and shows hysteresis effect.And in the initial stage of unloading,the steel sheet pile is in the ideal state of locking the pile wall under bending action,and gradually changes to the state of bending action of single pile with the process of unloading.3.Through further analysis,it is found that the change rate of slip and the change rate of deflection value fluctuate with the change of load,indicating that the lock between piles is in the continuous transformation process of "locking" and "loosening".4.According to the distribution law of the normal bending stress of the cross section,it is found that the stress distribution curve of the cross section is between the stress distribution curve of the single pile and the ideal pile wall,and the stress distribution curve gradually approaches the ideal pile wall value curve during the elastic loading stage.In addition,the stress distribution of the cross section is no longer linear due to the closer occlusion of the local lock along the pile body.