Study On The Mechanical Properties Of Simple-span Girder Bridge Based On Rigid Connection Widening

With the rapid development of China's economy,the increasingly close exchanges of regional economies,the changing of resident travel mode,the strong and growing morden logistics industry,closing to the saturation of the traffic volume of some sections of roads,especially the dramatical increase of large medium-sized vehicles and large tonnage transport vehicles,the traffic capacity of many secondary roads can't fulfill the growing social needs.So,the old roads and bridges should be widened to meet the needs of traffic.Based on typical bridges on secondary roads,the paper carried out researches on many issues,such as widening method of bridges,stress analysis of old and new bridges after reconstruction,concrete shrinkage and creep discrepancy influence of old and new bridges,the influence of the base's uneven settlement on superstructures.First,this paper summarized the widening and splicing methods of the existing bridges,and thereby built the bridge models by the finite element analysis software MIDAS,calculated the transverse load distribution and the horizontal distribution of the internal forces before and after widening bridge according to different ways of splicing methods.The results showed that internal forces of old bridges' beam under loading are reduced after widening,rigid-diaphragm beam connection is conducive to the overall stress of the bridge.Second,the article calculated and analyzed the influence of shrinkage and creep of concrete in superstructure and the joint of its connecting.The results showed that it was better to select rigid-diaphragm beam connection method between old and new bridges,and the storage time of the main girders should not be less than 90 days after established before forming with the old bridge.The relationship between shrinkage creep and span was further analyzed,and the results showed that internal force of shrinkage and creep was increased with the increase of span.Finally,the article calculated and analyzed the influence of different settlement between the old and new bridge's foundation in superstructures and the joint of its connecting,the results showed that the boundary beam of the old bridge was the most unfavorable under different settlement conditions,therefore it should be the main checking beam near the seam when bearing capacity of the old bridge.It was better to choose the rigid-diaphragm beam connection in the view of stress of the whole structure.The paper propssed the allowable settlement values of different bridges,based on the analysis results the actual support construction project under the most unfavorable settlement conditions.It should be controlled within 5mm for the simple T-beam bridge,while 10 mm for the simple hollow plate bridge.In general,the settlement allowance was generalized.And it should be controlled within 0.03 degree for the simple Tbeam bridge,while 0.08 degree for the simple hollow plate bridge,while the settlement rotation angle ? was used as the control index.The results of this paper could provide a useful reference on the design of similar bridges' expansion.