Study On Shear Lag In Cantilever Construction Of Different Box Girder Bridges

With the rapid development of transportation in China,more and more concrete continuous beam bridges and continuous rigid frame bridges are appearing in the traffic network,and the span is more and more large.The cross-section forms include single chamber single chamber,single chamber multi chamber and multi chamber and so on.the box section has unique stress characteristics.Shear lag effect is one of the mechanical properties of box girder.The shear lag effect leads to the uneven distribution of the cross section stress of the box beam,resulting in cracks and even damage.In the cantilever construction stage of the bridge,the main beam is subjected to large force,and the shear lag may affect the overall construction safety of the bridge.In this paper,the finite element model in the state of maximum cantilever under single-box,single-box and double-chamber girder bridges is established to simulate the shear lag effect of box girder under construction load.The shear lag effect of single box single chamber beam bridge and single box multi room beam bridge is compared and analyzed.The main conclusions are obtained as follows:(1)The characteristics of the shear lag effect are similar under the three loads of installing the hanging basket,pouring concrete and tensioning prestress.Under the action of prestressed tension,the shear lag effect near the cantilever end is the most significant.The location of the maximum value of shear lag coefficient is related to the layout of prestressed tendons,and the location stress of prestressed beam arrangement is larger.(2)The shear lag effect of the main girder closer to the cantilever end is more obvious,while the stress distribution of each beam far away from the cantilever end is more uniform,and the shear lag effect is less affected.(3)The section of the cantilever root of the box beam is a positive shear lag effect,and then gradually becomes the negative shear lag effect along the bridge span.The transition section of single box single room beam bridge is between 1 and 2,and the transition section of single box double room beam bridge is from 2 to No.4.(4)The diaphragm of single box double chamber girder bridge has little influence on the shear lag effect of box girder,and the difference of maximum shear lag coefficient is small,so the influence of diaphragm on shear lag coefficient can be neglected.