Research On The Optimal Design And Experiment Of Railway Pile Caps

Pile foundation has characteristics of high bearing capacity, little settlement, excellent seismic performance, which was wildly used in railway bridge construction. When railway pile cap which is an important part of pile foundation bear the upper bridge load transferred by the pier, that will allocate the load to each pile by a certain rule. There is no uniform design and calculation method for railway pile caps at present, rigid angle and configuration steel at the bottom of pile caps was constructively limited in code for design on railway bridge and culvert of our country. Through the way of combining experiment and theoretical analysis comprehensively analysis the force transmission characteristics of railway pile caps, optimization design and calculation method of railway pile cap, that plays an crucial role to guarantee the safety of railway bridge operation.At real bridge state, pier, pile cap, pile and soil are mutual and working together. The finite element model that considering the condition of bridge joint action, has too much number of elements and nodes, lead to computing dimension and low efficiency. The concept of equivalent stiffness was put forward in this paper, that take the constraints of pile caps equivalent to springs with a certain stiffness, was added at the bottom of pile cap. Simplified like this greatly reduce the amount of the finite element model calculation, that can do more specific analysis to pile cap.The engineering background of this paper are5pile cap of new railway construction Longhai passenger uplink a certain super major bridge number7pier and11pile cap of Lan Yu line a certain river super major bridge number25pier, burying reinforcement meter for long-term observation in the pile caps, testing the stress of reinforcement meter repeatedly and continuously at every major construction phase. Setting up5pile and11pile cap construction stage equivalent stiffness finite element model, comparing the theoretical calculation and the actual test results, analyzing internal stress transmission laws of pile cap. The result show that pile cap in flexible working state in the construction process. The tension zone and compression zone apparently exist along the height direction of pile cap, showing certain characteristics of bending. The load of pile caps is transferred through the inclined compressive bar formed between the bottom of the pier and the top edge of pile and the vertical compressive bar in the pier loading surface area, keeping structural internal force balance through tensile bar between piles.According to the force transmission characteristics of pile caps, analyzing the influence to carrying capacity of11pile cap that including pile spacing, thickness of pile caps, loading area, reinforcement ratio at the bottom of pile cap. The reasonable value of the pile spacing will directly affect the carrying capacity of pile cap. When the thickness of pile cap reach to a certain value, if keeping on increasing the thickness of pile cap, the carrying capacity of pile cap change little. When the reinforcement ratio at the bottom of pile cap is low, the steel bar yield when the pile caps destruction, that is a typical tensile bar destruction. When the reinforcement ratio reaches a certain value, as the reinforcement ratio continues increasing, the carrying capacity of pile cap remained basically unchanged, the destruction of pile cap in the form of concrete compressive bar destruction.Taking11pile cap for background, set up space truss model that has characteristics of railway pile caps. Proposed design calculation formula for compressive bar and tensile bar, summarize optimal design method of railway pile caps.