Study On Mechanical Properties Of The Railway Bridge Pile Cap

Pile cap due to its high carrying capacity, excellent seismic performance and small settlement and is widely used in construction of railway bridges. The pile cap is located in the key position of a connecting bridge structure, an important component part of pile foundation, the design should be given attention. Multiple transmission models were presented for pile cap design, each method has a certain limitation and scope of application, but has not been unified. Therefore need to study transmission mechanism and mechanical properties for pile cap, then proposing suitable calculation method for the railway bridge pile cap is very necessary. The primary contents and achievements are given as follows:The main factors affecting the ultimate bearing capacity and the force transmission and the damage mechanism of pile cap include the strength grade of concrete, the pile spacing, the cap thickness, the loads form, the reinforcement ratio and the reinforcement arrangement form. Through analysing various affecting factors, this paper sums up the variation of the vertical ultimate bearing capacity of pile cap with various affecting factors, studing the transmission mechanism and mechanical properties of pile cap under various factors, and defining the boundaries of various damage mechanism, providing theory basis for proposing suitable calculation method of the railway bridge pile cap design.The stress path in the elastic stage as well as the emerging, development and distribution characteristics of the cracks under external load are analysed, besides, the topology optimization under various loads for pile cap is done in order to understand the stress and the material distribution characteristics of pile cap. Based on this reason, this paper proposes the spatial truss model which is suitable for the design of railway bridge pile cap.With the provisions of the existing norms at home and abroad and international research results, based on the equilibrium of force, the strain compatibility conditions and the concrete softening constitutive laws, and combined with finite elements method calculation results, the bearing capacities formula quantitative of the tie, the strut compression and the strut splitting are amended. Comparing the calculation results by the method presented in this paper to the finite element results, analysis result shows that two calculated results are closely tallied. In addition, comparing the steel bar number calculated by this method to that calculated by "cantilever beam method" and "strut-tie method" shows that the results calculated by this calculation method are closer to the results calculated by the "strut-tie method".This paper bases on the representative projects6piles cap and15piles cap of the railway bridge as field test research objects, analysing the stress variation and distribution characteristics of each measuring point under the construction conditions, making finite element analysis for representative projects with considering the effect between pile and soil, and comparing with test results by stress or strain measuring points that are arranged on the steel bar at the bottom of the pile cap, the strut of the pile cap and on the cap side respectively, finally finding the change of the law is consistent. Field data furtherly verifies that the mechanical properties of the railway bridge pile cap meet the spatial truss model.