Structural Optimization Of UHPC Box Girder Bridge Deck System And Static Performance Test

UHPC(Ultra High Performance Concrete)thin-walled box girder with dense diaphragms is called UHPC box girder for short,which is a new type of structure between ordinary concrete box girder and steel box girder.This structure makes full use of the excellent mechanical properties of UHPC,so it can greatly reduce the selfweight of the beam body and increase the span of the bridge.UHPC box girder bridge deck system has good mechanical performance due to the bidirectional stress characteristics and UHPC strain hardening characteristics.Therefore,based on the existing research,this paper optimizes the design and reasonable value of the main structural dimensions of the UHPC box girder bridge deck system,and studies the mechanical performance of the optimized system.This paper mainly carries out research work from the following aspects:Based on the Beijiang Fourth Bridge in Yingde City,Guangdong Province,this paper combines the existing UHPC box girder literature and engineering examples to optimize the main design parameters of the original UHPC box girder bridge deck system,and obtains a set of optimal design parameters.After optimized,the UHPC volume of the whole bridge is reduced by 10.6% compared with the original design.The global and local force calculations of the finite element are carried out on the optimized UHPC box girder scheme.The global calculation results show that the optimized UHPC box girder scheme meets the specification requirements in the serviceability limit state and the bearing capacity limit state.The local calculation results show that the upper chord plate of UHPC box girder bridge deck system suffers the most unfavorable stress,so relevant tests should be carried out to verify whether the mechanical performance meets the engineering design requirements.The 1:2 scale model test of the optimized UHPC box girder bridge deck system is carried out.The linear elastic test shows that the optimized system has good mechanical performance.Under 6.3 times the partial wheel load of the designed vehicle,the bridge deck system is still within the online elastic stress range,with strong overload performance.The ultimate bearing performance test shows that the crack resistance and ultimate bearing capacity of the optimized system meet the engineering design requirements.Under the serviceability limit state,the experimental value of nominal tensile stress is 2.14 times of the design value;under the bearing capacity limit state,the experimental value of nominal tensile stress is 3.09 times of the designed value.Both of them have high safety reserves.Based on the French code,the crack resistance performance of the upper chord is analyzed.The results show that the calculated nominal cracking stress is close to the measured cracking stress.The analysis of crack resistance parameters shows that increasing the reinforcement ratio can increase the cracking stress of the bridge deck system,and increasing the height of the upper chord plate can improve the crack safety factor.The nonlinear finite element software ABAQUS is used to analyze the whole process of the experimental beam.The comparison between the calculated results are and the experimental results shows that the finite element model has good accuracy and applicability.On this basis,the parameter analysis is carried out to investigate the influence of the diameter of the steel bar,the height of the upper chord plate and the tensile strength and compressive strength of the UHPC on the mechanical behavior of the test model.The results show that the appropriate increase of the reinforcement ratio can increase the post-crack stiffness and ultimate bearing capacity;the increase of the height of the upper chord plate can increase the initial stiffness and ultimate bearing capacity;increasing the tensile strength of UHPC can increase the post-crack stiffness and ultimate bearing capacity;however,increasing the compressive strength of UHPC has no effect on the structural stress.