Static Experimental Research On Reinforced Steel Diagonal Braced Box Girder Structure Of High-speed Railway

The main bridge of the Weihe River Bridge on the Yinxi High-speed Railway is the first project in China to use the bridge type of box girder with reinforced steel diagonal braces for PC railway bridges.For the new structure of the steel diagonal braces outside the web,there are few materials and data that can be referred to,and its mechanical properties and stress characteristics are not clear enough,so it is necessary to carry out detailed mechanical research on this structure.This paper takes the reinforced steel diagonal braced PC box girder structure of Weihe Bridge as the research object and carries out the following research contents:(1)Using the finite element analysis software ABAQUS,the simulation analysis of the whole bridge and the part of the diagonal braces of the 60 m reinforced steel diagonally bracing simply supported girder bridge of the Weihe Bridge respectively.The work performance,internal force and stress distribution law of the whole bridge and the diagonal bracing part under the design loads of self-weight,prestressed,secondary dead load and train static and live load are studied.In the meantime,The ABAQUS plastic damage model and the extended finite element model were used to simulate the cracking behavior of the concrete flange plate by finite element simulation,and the law of crack development and extension is obtained,and then check and calculate the local stability of the steel pipe;(2)According to the calculation results of stress,displacement and concrete cracking calculated by ABAQUS,take the part of the diagonal bracing of the 13.6m segment within 1/4 of the beam length of the beam end where the stress of the concrete flange plate and the steel braces is larger,and Combined with practical factors such as the experimental site and equipment,the scale ratio of 1:2.5 is used to carry out the local scale model experiment design of the reinforced steel diagonal bracing,including the size design of the specimen,the design of the anchorage of the specimen and the layout of the measuring points,and the design of the loading scheme,Confirmation and selection and debugging of experimental equipment;(3)Carry out the static load experiment of the local scale model of the diagonal bracing.According to the loading scheme,the three reinforced steel diagonal bracing specimens are subjected to uniform loads through the I-beam at the corresponding positions of the rails on the flange plate when the rail actually acts,and collected the strain,displacement and crack development results of all measuring points under each tonnage during the loading process are compared with the stress,displacement and cracking results obtained by finite element calculation,and then the force transmission mechanism and failure mode of the stiffened steel pipe diagonal braced box girder are determined.And the law of the development and extension of concrete cracks..The research shows that the experiment results are in good agreement with the results of the finite element calculation,and they all show that the Weihe Bridge reinforced steel diagonal bracing structure is in the elastic stress stage under the design load,and the steel tube bracing and the concrete flange plate stress are both small;Under1.25 times of the design load,longitudinal cracks are formed on the bottom surface of the concrete flange plate and gradually extend along an included angle of about 10°with the horizontal direction;Under 3 times the design load,the end of the steel tube diagonal bracing locally reaches the yield strength of Q345 q D material,many cracks on the bottom surface of the flange plate are connected,and the overall stress of the structure is good without obvious damage and large deformation.