Research On Reinforcement Design Of Mass Concrete Pile Cap Based On Strut And Tie Model

As an important component to transfer the upper load in the pile foundation design,which is widely used in highway bridges due its high bearing capacity,strong earthquake resistance and inhomogeneous settlement for various foundations.With the rise of all kinds of huge bridges,larger and thicker and more pile of caps are increasing,the corresponding reinforcement methods should be emphasized in the design.Therefore,it has important theoretical significance and engineering reference value to study the load transfer model and the reinforcement method.This paper based on the achievements of previous researchers,combined with relevant norms and documents,with the actual project as the background,taking the pile concrete cap of pile group as the research object,the reinforcement of concrete cap is studied in depth.The contents of this paper are as follows:(1)The design methods of pile caps in domestic and foreign codes are elaborated.The theoretical basis and shortcomings of the design methods of pile caps in different codes are compared.The research status of pile caps at home and abroad is discussed,and some problems existing in the design of pile cap reinforcement are put forward.In the definition of concrete zoning,the caps belong to the structure of D area is cleared,and the basis of the theory of strut and tie models is introduced.The strut,tie and node are introduced in detail,and the applicability of each design method in the strut and tie model is listed in tabular form.The design criterion of strut and tie is elaborated,the research progress and application of strut and tie model are summarized,and the basic steps of designing strut and tie reinforcement are put forward.(2)Based on the actual project,the finite element model of pile group cap is established,the stress and flow condition of pile cap under the action of operation load is analyzed.On the basis of the finite element model,the range of parameter is determined.Topology optimization method is adopted to establish the optimal result of the strut and tie model of the cap,which meets the strength checking computation.The results of different design methods are compared with the current standard calculation method.The results show that the amount of reinforcement calculated by the pull and pressure bar model method saves the reinforcement than the current standard.Through the node balance method,the distribution law of pile top reaction is analyzed,and the influence rule of pile cap thickness and pile-soil rigidity is determined.(3)Combined with the finite element theory of reinforced concrete,the reinforcement of the reinforced bar model calculated under the operating load is calculated.The results show that the reinforcement structure of the tension and compression bar is safe and feasible under the operation load.The influence law of the bearing capacity of the structure under the different reinforcement form and the different reinforcement ratio is analyzed in detail.The results show that the load capacity of the bearing platform can be improved by the concentrated reinforcement in the pile diameter compared with the uniform reinforcement.The reinforcement ratio of the pile cap presents a nonlinear growth rule for the bearing capacity,the reinforcement will not significantly improve the bearing capacity of the cap with a certain reinforcement ratio.Finally,combined with the calculation results,the engineering design recommendations for the load reinforcement of the cap are put forward.(4)Combining the finite element theory of the early concrete temperature stress,the influence of the steel bar on the stress of the early concrete is analyzed by the finite element model,and the effect of the reinforcement on the crack resistance of the concrete is explained with the actual engineering data.Taking the temperature crack index as an index,the influence rule of reinforcement spacing and reinforcement diameter is analyzed.Based on the reinforcement principle of crack control,the engineering design suggestions for not carry stress reinforcement of caps are given.