| During the infrastructure boom of the past three decades in my country,bridge building has proceeded at a rapid pace on a vast scale.PC box girder bridges are one of the preferred type of bridge within the main spanā„200m.This type of bridge has the merit of this bridge are low cost,simple and convenient construction,and low maintenance costs.while,considering the inherent properties of its own materials,PC box girder bridges have been found to have two major drawbacks in the long-term service: excessive deflection and beam cracking.Studies have shown that excessive deflection in beams causes undesirable effects as cracks get worse and continue to develop.The combination of causes of both phenomena in large span bridges is attributed to the structural deficiencies,which limits the development of PC box girder bridges to a great extent noticeably.Associated with Research and application of Ultra-High-Performance Concrete(UHPC),the UHPC R&D team of Hunan University proposed a dense diaphragm UHPC thin-walled box girder structure,which considers the box-shaped section in accordance with UHPC optimization.Moreover,this study covers the design features of the multi-stiffening structure inside the steel box girder in order to address the two major problems of PC box girder(mid-span deflection and beam cracking).The team has carried out a series of experimental studies on the new UHPC box girder structure and has a certain understanding of its structural performance.Relying on the engineering project,this paper analyzes and studies the flexural performance of segmental prefabricated and assembled external prestressed UHPC box girder.The main research contents are as follows:(1)Based on the engineering background of the approach bridge over the side embankment of Dazhan Town,Beijiang Fourth Bridge,Qingyuan City,Guangdong Province(single-span 102 m UHPC simply supported box girder bridge),this paper uses the Midas Civil software to establish a full bridge model based on the project and to conduct an overall analysis.The calculation results show that: a)The ultimate bending and shearing capacity of the UHPC box girder scheme meets the engineering design requirement.The safety factors of the bending bearing capacity at the mid-span section and the joint section are 1.34 and 1.17 respectively.b)The stress level of the UHPC box girder scheme considering under the serviceability limit state,serves the purpose of the relevant specifications for the fully prestressed member,indicating that the UHPC box girder structure can give satisfaction to engineering design demand.(2)According to the experimental research requirement,a 1:4 scaled test beam was designed and manufactured.Two point bending test was carried for study to observe the crack development and its trend,and ultimate bending and destruction form of the test beam during the test.(3)Using ABAQUS software to track and analyze the entire loading process of the test beam,and compare the finite element analysis and the structural response of the test process to verify the accuracy of the finite element model.Based on this finite element model,a series of parameters such as UHPC tensile and compressive strength,external prestressed beam reinforcement ratio and permanent stress are set for finite element analysis,and the influence of these parameters on the bending performance of the test beam is summarized and analyzed.(4)The flexural bearing capacity of the segmental prefabricated and assembled external prestressed UHPC box girder is calculated and analyzed,and the simplified calculation formula is derived through the equivalent rectangular stress distribution diagram.The calculation results show that the contribution of UHPC tensile strength is more consistent with the finite element analysis results. |
PDF Full Text Request