Study On Temperature Field And Effect Of Long-span Curved Prestressed Concrete Box Girder

Along with the development of high-grade highways and urban overpass,curved box girder has been widely used because it can meet the needs of the terrain and route design.Temperature effect is an important factor to cause the disease of curved box girder.Therefore,it is of practical significance to analyze the temperature field and temperature effect of curved box girder.In this paper,using the finite element software ANSYS,the solid model of Changfeng L14 curved box girder is established.Combining with the actual weather situation of bridge site,the temperature field and temperature effect of curved box girder under three types of temperature loads including the annual temperature variation,solar radiation and sudden drop in temperature are analyzed.By studying middle section and fulcrum section,the variations of box girder temperature field with time during the day are concluded.And temperature effects of curved box girder under different support distributions are compared.The specific contents are mainly as the following aspects:(1)The current research situation on the temperature of the concrete box girder at home and abroad is introduced,and the basic theory on the temperature field and the temperature effect of the concrete box girder is summarized.(2)The temperature deformation and stress under different ranges of integral overheating and cooling is calculated,at the same time,the temperature effect of the box girder when the roof temperature rises is also compared.Variation of deformation displacement and stress of box girder under temperature variation is is linear;When the temperature rising,the box girder is in the stress state of the " curve outside tension and inside compression",which is the opposite when cooling;When the roof is heated,the beam will have great stress,and the vertical deformation of the box girder will be changed greatly.(3)The temperature field and effect of the curved box girder under sudden cooling and certain sunshine radiation are analyzed.In the two case,the temperature of the outer surface of the box girder with stronger heat transfer capability is more close to the corresponding environmental temperature;Sudden cooling the curved box girder will be in the linear state of "middle span arching and side span sinking",which be the opposite when heating;Large tensile stress occurrs in the flange under sudden cooling,and the tensile stress of the midspan baseplate under solar radiation is also very large,therefore temperature crack may be formed easily in these places.(4)The time-varying temperature field of middle section and fulcrum section in daytime is simulated,and the temperature distribution of different thickness is compared.In summer,the roof surface temperature range of the box girder is the biggest,which can reach 24?;The internal temperature change of the roof is about 2 hours lag behind the surface;The internal surface temperature of the box girder has been rising at a relatively constant rate,the greater thickness of the roof and floor,the smaller internal surface temperature range of the box girder.(5)Change the curve box girder bearing arrangement to get four kinds of constraints,then use Ansys to compare four kinds of the box girder temperature effects under different constraint conditions.Using single point constraint at middle pier will reduce the lateral stability of the bridge;Restricting tangential displacement of curved box girder at different piers can lead to larger internal temperature stress.Fixed support should be set at the middle pier to reduce temperature displacement of the end of box girder.