Research on Key Design and Construction Techniques for Precast Segmental Box Girders of Sharp-Radius Ramp Bridge
To promote the application of precast segmental box girders in the sharp-radius ramp bridge,studies were carried out to analyze multiple related issues,including mechanical property,effective structural configuration,girder fabrication as well as the crane installation and girder assembly alignment control.The relationship between the radius of the ramp bridge and the torsional-flexural resonances as well as load bearing behavior of cast-in-situ stitches was examined.The effects of girder depth,web thickness,and top and bottom slab thicknesses to the shear and torsional resistance of the girders were investigated.To suit the plan curvature of the ramp bridge,the girders were erected by cranes,during which tailored techniques were taken to smooth the construction,including guiding the cranes to turn and cross the piers,adjusting the girder offset,tuning the unbalanced hoisting,and feeding girders from end.The measures to adjust the axis deviation,lateral displacement and alignment during construction were analyzed.It is shown that during the construction of the precast box girders within a plan curvature radius smaller than 250 m,the torsional-flexural resonances must be considered,while within a plan curvature radius smaller than 100 m,the torsional resistance and allowable cross-sectional shear-torsional stresses can not meet the requirements.The most effective way to improve the cross-sectional shear-torsional resistance is to increase the thickness of the webs,and increasing the thicknesses of the top and bottom slabs is also applicable.The smaller the plan curvature radius,the greater the assembly axis deviation of the box girders and the axial lateral displacement.The acceptance criteria for the assembly accuracy should be determined in accordance with the plan curvature radius of the ramp bridge,and the pre-cambers of the superstructure should be set with the consideration of the axial lateral displacement of the completed ramp bridge.
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维普
