Temperature Gradient Study And Effect Analysis Of PK Section Steel Box Girder In Asphalt Concrete Pavement

Under the action of sunshine temperature,the temperature gradient generated by the wide-section steel box girder of the cable-stayed bridge in the operation stage is likely to cause relatively large temperature stress.Although the Chinese highway bridge specification JTG D60-2015 gives the vertical and lateral temperature gradient of the structural section.However,it is worthy of more detailed research on the application of bridge structures in different regions and different sections.In this thesis,the four-bridge of Luzhou Tuojiang River in the operation stage is used as the engineering background.The temperature field of the PK section steel box girder with asphalt concrete pavement is measured by ANSYS and the ANSYS finite element simulation.The full bridge model is established by MIDAS Civil and will be fitted.The temperature gradient mode and the recommended mode are loaded,and the effects of the temperature effects of the cable-stayed bridges are compared between the two modes.The main contents and results are as follows:(1)By simplifying the boundary conditions of the integrated heat transfer coefficient h and the integrated atmospheric temperature Tsa,the ANSYS model of the sunshine temperature field of the asphalt pavement PK steel box girder is established.The results show that the surface of the asphalt concrete pavement layer is at 14:00 on a sunny day.When the maximum value is reached,the temperature of each plate of the steel box girder reaches the maximum temperature at 18:00,and the temperature field of the steel box girder shows obvious hysteresis.The vertical maximum positive temperature difference of the longitudinal partition of the finite element simulation is 14.26℃,which is a nonlinear mode.By changing the calculation parameters,the vertical temperature difference between the steel box girder and the lateral temperature difference of the roof plate are ranked from the largest to the smallest in order of the pavement layer absorption rate,atmospheric transparency,wind speed,pavement layer thickness and steel absorption rate.(2)The 7-month temperature measurement of each panel of PK steel box girder was carried out.The results show that the lateral temperature difference of the steel box girder with pavement layer is mainly manifested on the U rib of the top plate and the top plate,and the lateral temperature difference between the U rib of the bottom plate and the bottom plate is not obvious.In the typical summer weather,the U rib of the top plate reaches the lowest temperature and the highest temperature lags behind the top plate.The lateral temperature difference of the roof and the vertical positive temperature difference of the longitudinal partition are related to the intensity of solar radiation.The sunny day is the largest,the cloudy day is the second,and the rainy day is the smallest.The maximum positive temperature difference measured by the longitudinal partition is 16.25℃,which is a nonlinear mode.The maximum negative temperature difference of the vertical partition is-2.5℃,which is linear.The maximum lateral temperature difference of the top plate is 15℃.The temperature gradient mode can be fitted to the "N" type..Comparing the measured temperature and the calculated temperature of the measuring points of the steel box beam,the results are in good agreement,indicating that the finite element simulation is accurate.(3)The most unfavorable temperature gradient fitting of the vertical box with PK section steel box girder with pavement layer indicates that the vertical positive temperature difference mode can be simulated by exponential form;the vertical negative temperature difference mode can be simulated by linear equation.It can be seen from the measured worst-case temperature gradient that the maximum vertical negative temperature difference base of the PK steel box girder with asphalt concrete pavement is-0.154 times the maximum vertical positive temperature difference base.Comparing the fitted temperature gradient with the temperature gradients of various countries,the British BS-5400 specification value is selected as the recommended mode;the measured lateral temperature difference base of the roof is far greater than the specified value given by the Chinese highway bridge specification JTG D60-2015,it is necessary to consider the horizontal Temperature gradient.(4)Comparing and analyzing the temperature effect produced by fitting temperature model and recommended temperature model,the results show that it is feasible to use BS-5400 specification to load the section temperature gradient of steel box girder of cable-stayed bridge in the absence of field temperature gradient in Luzhou area.