Joint Design And Model Tests Of Extra-long-span UHPC Continuous Girder Bridge

The extra-long-span continuous box girder bridge composed of ultra-highperformance concrete (UHPC) was put forward which was based on the excellenttensile and compressive properties of UHPC. The new beam bridge is the organiccombination of UHPC, thin-wall box girder with dense diaphragm plates, and partialexternal prestressing technique, and it changes three-dimensional prestressedstructure into one-dimensional prestressed structure in the longitudinal of bridge.Compared with the traditional continuous girder bridge, it has the advantages of largespanning, light deadweight, strong stability, small deflection at mid span of lateroperation, easy to maintenance etc. With the precast segment cantilever method, abracket joint between segments is proposed for the extra-long-span UHPC continuousbox girder bridge, and conduct parameter optimization analysis. This passage focuson the shear performance of single bracket joint, investigate the effects of diaphragmon the shear performance, and research whether the vertical joints of box girder webscan meet the force demand of structure. In view of this, the author has done thefollowing work:(1) Establish joint finite element analysis model, and use the result of numericalanalysis to contrast the shear performance of conventional concrete joints with UHPCjoints. In addition, investigate the shear performance of single bracket joints and toothblock joints and conduct parameter optimization analysis on UHPC bracket joints.The parameter optimization is done for the following parameters, including thehorizontal angle of bracket joint, the ratio of joint tooth block’s depth and height, andthe ratio of joint tooth block’s height and beam’s height. The optimal ones are0~45,great than1/10, and1/3~2/3correspondingly.(2) A double cantilever box girder with bracket joint is designed by theoptimization, one end of the beam has three diaphragm plates while other one hasfour diaphragm plates. Compared with the shear performance of the two cantilevergirders under elastic load, also study the whole course of shear failure of the twobeams through the experiment. The results demonstrate that the shear behavior ofweb’s joint is strong, and the shear capacity of joint can be increased by intensivediaphragm plates in thin-walled box girder. The cracking strain in joint’s corner reached455με, which is much greater than the ordinary concrete joint, and theresistance cracking degree of safety reach to1.63.(3) Establish finite element analysis model of test beam. Combining with modeltests and numerical analysis, the shear behavior of web’s joint and the influence ofdiaphragm plates on the joint performance are studied. The results demonstrate thatthe shear behavior of UHPC bracket joint is strong, and the shear capacity of jointcan be increased by intensive diaphragm plates in thin-walled box girder.(4) Brief introduce the continuous girder bridge whose span is up to400m span,besides, establish MIDAS finite element analysis model of whole bridge to analyzethe overall force of the whole bridge and the shrinkage and creep properties. Theresults demonstrate that the stress distribution of extra-long-span continuous boxgirder bridge composed of UHPC is uniform which conform to the force demand ofstructure, and the deflection at mid span of later operation is small which can avoidthe risk of bridge crack.(5) Basing on the global model, establish the local finite element model of thesegment near the bearing to analyze its mechanical behavior, determine if the shearcapacity of the webs and joints can satisfy the requirements of the box girder. Theresults show that bracket joints keep good connectivity and integrity, and the principaltensile stress of the webs and joints is relatively low, it will not make the webs crack,which means the girder can satisfy the force requirements of the ultra-long spanbridge.