Study On Bearing Behavior Of Pile-beam Composite Spatial Foundation Structure

For a long time,pile foundation has been widely used in all kinds of engineering construction.However,because the group pile foundation of high(heavy)buildings often set long pile length due to bearing capacity demand and deformation demand,and the ability of group pile foundation to resist lateral load is relatively weak,there are engineering problems of insufficient bearing capacity or large horizontal deformation in some specific enviro nment.Therefore,in this paper,a new structural type of pile-beam combination space foundation is proposed on the group pile foundation,which can make full use of the shallow reliable bearing layer bearing capacity under the premise of satisfying the vertical and horizontal bearing capacity and deformation requirements of foundation engineering,so as to achieve the purpose of reducing the number of foundation piles,shortening the pile length and reducing the engineering construction difficulty.In this paper,through theoretical analysis and calculation,numerical simulation and other methods,the bearing behavior of pile-beam combined space foundation structure under vertical and horizontal loads are studied and compared with those of group pile foundation,the main work is as follows:(1)The 2×2 group pile foundation was modeled by software,and its vertical load carrying and horizontal load carrying behavior were studied in terms of different pile spacing,load transfer settlement characteristics under different loads,pile axial force,pile end resistance,horizontal load-displacement and pile bending moment.(2)Modeling and analysis of pile-beam combined space foundation structure by software,and study its vertical and horizontal bearing behavior by changing the number of beam layers,pile spacing,load level and other different working conditions,and compare and analyze the bearing behavior with those of conventional group pile foundation.(3)Vertical bearing behavior: the settlement of the pile-beam combined space foundation structure under different pile spacing gradually increases with the increase of load level.Under the same working condition,compared with group pile foundation,the pile-beam combined space foundation structure will effectively reduce the settlement value;the pile-beam combined space foundation structure has an obvious abrupt change in pile axial force at the cross beam;the pile-beam combined space foundation structure pile axial force under each pile spacing decreases with the increase of pile depth,and the magnitude of axial force decrease increases with the increase of load level.With the increase of pile spacing,the maximum value of axial force under each load level decreases;the difference of pile end resistance o f pile-beam combined space foundation structure under different pile spacing increases gradually with the increase of load level;under the same load level,the pile end resistance decreases with the increase of pile spacing,and under the same working condition,compared with group pile foundation,the pile-beam combined space foundation structure will effectively reduce the pile end resistance.(4)Horizontal bearing behavior: Within the range of the added load,the horizontal displacement at the center of the top of the bearing platform of the combined pile-beam spatial foundation structure under each pile spacing is approximately linearly related to the horizontal load.Under the same working condition,compared with group pile foundation,the pile-beam combined space foundation structure can effectively reduce the horizontal displacement;under the same load level,with the increase of pile spacing,the maximum positive and negative bending moment values of the pile-beam combined space foundation structure pile body are decreasing.Compared with the group pile foundation,the pile moment of the pile-beam combined space foundation structure has a negative moment zone at the bottom side of the crossbeam,and the maximum positive and negative moments of the pile body of the pile-beam combined space foundation structure are significantly reduced compared with those of the group pile.(5)By summarizing the calculation methods of the bearing capacity of the group pile foundation in common use nowadays and combining with the elastic foundation beam theory,the calculation ideas of the bearing capacity of the pile-beam combined space foundation structure are proposed.