Research On The Torsion Performance Of I-section Steel-concrete Composite Dual-girder Bridge

The I-section steel-concrete composite dual-girder bridge is an open-section structure composed of a concrete roof and two H-shaped steel girders through transverse connection system.It combines the advantages of two materials and is easy to construct,it is a promising structure type in small and medium-span bridges.The webs of conventional open-section composite girders are flat steel plates.In recent years,corrugated steel plates have been widely used in closed-section composite box girders and have good mechanical performance,but corrugated steel plates are fewly used in open-section composite girders.Therefore,a kind of open-section dual-girder bridge with corrugated steel webs is proposed in this paper.It replaces the flat steel webs with corrugated steel webs.And by comparing the results of these two kinds of girders,the influence of web shape on the overall torsional performance of composite dual-girder bridge is studied.For now,studies of the torsional performance of open-section composite girders are mainly based on single girders.This will ignore the influence of the transverse connection and the distance between steel girders on the torsional performance of composite girders with the increase of the number of main steel girders.In this paper,the general frame-type cross brace and truss-type cross brace used in open-section composite girders are selected to investigate the effect of the distance between the steel girders and the kind of lateral connection on the overall torsional performance of the composite girders.The main contents and conclusions of this paper are as follows:(1)Three dual-girder bridge test models are designed and fabricated with variable web shapes and lateral connections,and the pure torque loading test is completed.The development and distribution patterns of the crackings in the girders are obtained,and the torque during the whole process of torsion is obtained.Twist rate curves,stress and strain distributions of concrete plates,webs of steel girders,lower flanges of steel girders and steel bars are given in this paper.The test results show that under the pure torsion effect of the composite girders,the steel bars area yielded and cracks along 45° extend so much that the deformation of the concrete plates is too large and the composite girder is considered to be destroyed.Concrete and steel girders are axially restrained during torsion,and are both under restraint torsion.The transverse connection affects the distribution of shear flow in the section,and thus have influence on the torsional behavior of the composite girder.The difference in the slope and maximum of the torque-torsion curve of the composite girder with the corrugated web and the flat web shows that the shape of the webs has a certain influence on the torsional stiffness and ultimate bearing capacity of the composite dual-girder bridges.(2)By comparing with the test results,the way of applying torque that best fits actual loading process can be obtained.the best simulation method that can perfectly reflect the real performance of the composite dual-girder bridge under pure torsional load is obtained.The finite element model of each test girder is established.Through the comparison between the finite element model results and test results,it is found that the effect of the web shapes and lateral connection of the steel girders on the torsional behavior of open-section composite dual-girder bridge is mainly limited to plastic and destruction range,and the corrugated steel plate is less effective than the flat steel plates in resisting torque.The existence of the lateral connections will increase the overall torsional stiffness and ultimate bearing capacity of the composite girder.(3)Based on the I-section steel-concrete composite dual-girder bridge with flat webs connected by small beams,this paper studies the effect of several variables on torsional performance including the distance of beams,the distance between steel girders,the strength grade of concrete and the reinforcement ratio of the concrete roof.The results show that the space between the small beams has no obvious influence on the torsional performance of the combined dual-girder bridge.Increasing the distance between steel girders can significantly increase the cracking torque,torsion bearing capacity and torsion stiffness of the combined dual-girder structure.Improving the strength grade of concrete can increase the cracking torque,torsion bearing capacity and torsion stiffness of the composite dual-girder structure to some extent.Increasing the reinforcement ratio of the concrete roof can mainly improve the torsion behavior of composite dual-girder at plastic stage.