Load Transfer Across Shear Keys In Steel Pile-to-pile Cap Connection

Steel pipe piles are widely used in the pile foundation engineering of port wharf in China because of their high bearing capacity and simple construction procedure.In order to ensure the reliability of the connection between steel pipe piles and the beam of wharf superstructure,one or more shear keys are usually welded at the top of piles and then a section of pile-core concrete is cast on the top of piles.The shear keys are connected with pile-core concrete and steel pipe.A force system is formed between them,which plays the role of transferring load.However,the stress mechanism of steel tube pile shear key is relatively complex,and there is no corresponding conclusion in the current code of our country.However,as an important way to transfer load,the analysis of the stress mechanism of steel tube pile shear key is imminent.One of the most important and difficult problems is how to determine the distribution coefficients among the keys in the case of multiple pairs of keys.In view of this,based on Gebman's measured data and under the condition of axial compression,this paper makes a tentative theoretical exploration on the distribution coefficients of each keys based on the theory of tension-compression rod model,and establishes a finite element model of steel pipe pile shear key.The theoretical calculation results,numerical simulation results and Gebman's measured data results are compared,and the results show that the calculation accuracy is higher.The determination of distribution coefficient not only lays a foundation for calculating the stress distribution function of pile-core concrete,but also provides a reference for the design of many pairs of shear keys.Specific research contents are as follows:(1)According to the stress characteristics and stress transfer mode of steel tube pile shear key pile core concrete,and considering the restraint effect of steel tube wall on pile core properly with the theory of tension-compression rod model,the calculated results are in good agreement with the measured values and numerical modulus values,which shows that the method is effective in determining the distribution coefficient of multiple pairs of keys.(2)By further extending the calculation formula,it is found that the distance between keys is an important factor affecting the distribution coefficient between bonds under pressure,and the sensitivity intervals of two and three pairs of keys are obtained.The stress sensitive region of two pairs of keys is 75 mm ~ 200 mm,and the sensitive region of three pairs of keys is 100 mm ~ 150 mm.With the increase of the number of keys,the sensitive region will be compressed.In addition,under the condition of axial tension,it is also found that the time distance between 75 mm and 190 mm has a significant effect on the distribution coefficient of the keys.When the distance is greater than 190 mm,the influence of the distance on the distribution coefficient is gradually weakened.In the case of three pairs of keys,the sensitive area of the spacing is between 100 mm and 150 mm,which provides a reference for the layout optimization of subsequent shear keys.(3)The distribution coefficient varies with the diameter of steel tube.The larger the diameter of steel tube,the lower the distribution coefficient of the first key and the higher the distribution coefficient of the second key.When the diameter of steel pipe increases to 4.0m or more,the influence of pile diameter on the distribution coefficient of key decreases gradually,which indicates that when the diameter of steel pipe increases to a certain extent,the influence of pile diameter on the distribution coefficient of key will no longer be significant.(4)The theoretical formula can determine the distribution coefficients among the keys,which lays a foundation for analyzing the failure mechanism and cracking mechanism of the shear keys,and provides a new method for discussing the stress mechanism of the shear keys step by step.In this paper,the concept of distribution coefficient is put forward and the corresponding calculation formula is obtained for the connection mode of shear key of steel pipe pile with the beam of superstructure.It provides a certain basis for the reinforcement calculation and optimization design of pile-core concrete and further theoretical analysis,and also provides a certain reference value for future engineering design.