Research On Temperature Field Of Steel Box Girder And Thermal Stress Of Structural Details Of Orthotropic Steel Deck

In order to investigate the temperature distribution of steel box girder under solar radiation and the effects of temperature gradient on stress at structural details of orthotropic steel deck(OSD),in this paper,the temperature field of two steel box girder bridges is measured,a sectional model of box girder is established for finite element analysis of temperature field,the finite element results on the floorbeam are compared with the measured results,the thermal stress produced by temperature field at structural details of orthotropic steel deck and its influence on the fatigue life of the structure are studied by sub model technique.The main contents are as follows:(1)the temperature on outer circumference and the floorbeam of two steel box girders is measured under strong solar radiation and high environmental temperature in summer and the typical sunny weather in four seasons,and the vertical temperature gradient is fitted based on measured maximum temperature difference between roof and floor,the factors affecting the transverse temperature distribution are analyzed and suggestions on the transverse temperature gradient are put forward.It is found that under strong solar radiation and high environmental temperature in summer,there is the maximum vertical thermal gradient on the steel-deck box girder and it can be fitted as a combination of four linear functions after revising the interpolation point and the interpolation temperature,with the maximum temperature difference is lower than that of Eurocode.There is no obvious gradient function on the transverse temperature distribution,but the factors such as bridge direction,inclined web,pavement thickness of bridge deck system,guardrail position and longitudinal space plate will affect the transverse temperature variation,it is suggested that the linear temperature gradient should be considered in these areas.(2)After establishing the sectional model of box girder in ANSYS with measured temperature and convection conditions applied on box-girder,temperature field in the sectional model is obtained.The results on floorbeam agree well with the measured temperature,which validates the present th ermal analysis.(3)The sub model of OSD in the sectional model of box girder is established based on the sub model technology,and the refined grid is divided in this model.Based on the 24 h temperature field,thermal stress field in the sectional model of box girder is analyzed,then,the thermal stress time histories at the four details around rib-to-floorbeam connection and the cutout are obtained in the sub model.It is found that obvious thermal deformation and significant stress concentration appear at the details of OSD,particularly stress ranges at rib-to-floorbeam of rib side and at the cutout are higher than that at rib-to-floorbeam of floorbeam side and weld-all-around.The stress at cutout is tensile stress,it is very high and the first principal stress at cutout is tangent to it free edge,perpendicular to the crack direction in the real bridge.Thermal stress may affect the cracking of cutout.(4)The effect of thermal stress on the fatigue properties of four structural details is studied,the hot spot stress is used at three details around rib-to-floorbeam connection,and the nominal stress is used at the cutout.It is found that the four structural details all meet the requirements of infinite life under the action of temperature load.But it may be detrimental for the thermal stress to be superimposed over the live-load induced stress range at detail s of OSD.Hence the effect of thermal stress on fatigue performance of OSD should be taken seriously.