Study On Solar Radiation And Hydration Heat Hemperature Field Of Box Girder In High Altitude Area Of Southern Tibet

The bridge structure is exposed to the natural environment all year round,and it will inevitably cause some adverse effects on the bridge itself due to the influence of sunshine radiation,the change of day and night temperature.Especially,the prestressed rigid frame bridge,which is built in high altitude area with large temperature change and strong solar radiation,may have more influence.This paper takes a prestressed continuous rigid frame bridge as the research object,and constructs the box girder segment model.The analysis and Research on the temperature field of the real bridge section and box girder model are carried out,and the main results are as follows:The vertical temperature difference of the solar radiation temperature field of the real bridge section reaches the maximum value at 15:00,and at this time is the highest time of the overall temperature of the box girder.The highest temperature measureme nt point is located on the top surface of the top of the box girder roof,and the lowest temperature measurement point is located on the top surface of the box girder bottom plate.The temperature change of roof > Web temperature > the temperature change of bottom plate during the whole day.The vertical temperature gradient of the positive side and the back side of the bridge under the influence of solar radiation is compared.The vertical overall temperature of the positive side is higher than the vertical overall temperature of the back yang side under the influence of solar radiation.The temperature measurement points of the web at the positive side are obviously concave than the temperature of the top plate and the bottom plate.The temperature of the web at the top and lowest temperature of the back side web is almost unchanged.The temperature distribution of the web at the back side can be simplified to a "1" shape distribution.At the lowest temperature,the temperature difference between the roof and the other measuring points is not significant.Then,under the influence of solar radiation,the temperature of the roof measuring point rises rapidly,and the maximum temperature difference between the roof and the bottom plate measuring point reaches 10.8 ℃.The temperature of hydration in the box girder section changes obviously within 72 hours after pouring,and the hydration temperature is distributed symmetrically along the web of the box girder.The initial temperature distribution of the temperature field of the point array model is relatively uniform.After 6 hours of pouring,the box girder concrete begins to release heat gradually,and the overall temperature of the box girder model begins to rise.Because the roof of the box girder can conduct heat exchange with the external environment,the temperature rise is relatively slow.When the pouring is completed for 12 h,the peak value of hydration heat temperature of box girder appears,and the peak measurement point is located at the junction position of the middle web and the bottom plate,and the peak temperature is 28.9 ℃.During the 12-16 h process after pouring,the hydration heat temperature of box girder will remain unchanged.After 17 h of pouring,the temperature of the web and bottom plate of box girder began to decrease gradually,and the hydration and heat release process of box girder was 72 h after the completion of the pouring.The temperature of the box girder model is fitted along the thickness of the plate in the hydration heat stage.It is found that the temperature and thickness of the roof are approximately linear,while for the web and the bottom plate,the temperature and thickness are approximately quadratic function.The transverse temperature of roof and bottom plate in the hydration heat stage of box girder model is fitted.The hydration temperature is symmetrical distribution,and the three peak mode is along the width direction.The peak points are all located at the junction position between web and top floor.The peak value of middle peak is higher than that of both sides,and the maximum average temperature in the direction of roof width is 29.8 ℃;The maximum average temperature of the width direction of the bottom plate is 29.1 ℃.The temperature change of box girder under the influence of solar radiation is divided into stable stage,heating stage and cooling stage.The temperature of web is the lowest at 8:00,then the temperature gradually increases,reaching the highest temperature at 15:00,and the maximum temperature gradient of the measured model is 15.1 ℃.Compared with the heating stage of each part,the temperature change of the middle web and the bottom plate is small.Compared with the cooling stage of each part,it can be seen that the temperature of the roof position decreases rapidly in the period from 15:00 to20:00,and the temperature of web part decreases rapidly in the period of 20:00-23:00.The temperature of box girder section tends to be stable from 0:00 to 8:00,and the temperature of each part is not changed.The temperature field of hydration in the section of box girder is simulated by finite element method.The variation law of hydration heat temperature obtained by FEM is consistent with the measured one.The factors influencing the distribution of hydration heat temperature are analyzed.Among the factors affecting the temperature field of concrete,the factors influencing hydration heat are arranged according to the maximum temperature difference of the section.The cement content in unit volume > the temperature of the mold is > the heat conduction coefficient > the model size.