Analysis Of Vertical Temperature Gradient And Temperature Effect Of Unpaved PK Section Steel-concrete Composite Beam

Steel-concrete composite beams are widely used in cable-stayed bridges due to their good mechanical properties and economy.When the composite beam is exposed to sunlight,due to the hysteresis of heat transfer and other reasons,the structural temperature presents a significantly non-uniform and nonlinear distribution in the vertical direction.This causes large self-stresses in the structure and,when constrained,secondary stresses.Therefore,the temperature gradient often becomes the controlling factor in the design of the composite beam.At present,there have been a lot of studies on the sunlight temperature gradient and its effects on concrete beams and steel beams with box sections.However,there is no research on the temperature field of composite beams with PK section.Moreover,the current code in my country does not stipulate the value of the temperature gradient of the composite beam without pavement.This paper takes the main channel bridge of the Zhongkai Expressway Yinzhou Lake Bridge as the engineering background.The temperature gradient and its effect of steel-concrete composite beams with unpaved PK section in the construction stage are studied.The main work and conclusions are as follows:(1)A typical section is selected to measure the temperature field of the steel-concrete composite beam with PK section without pavement in the middle span of the construction stage.Through the analysis of the measured data,the temperature distribution characteristics under different weather conditions are obtained.It is found that the roof has a distribution law that the temperature gradually increases at the same time as the distance from the top surface of the beam decreases in the vertical direction.The web temperature of the steel box varies relatively little with height in the vertical direction.At the interface where the concrete roof and the steel beam web are connected by shear studs,the temperature at the middle web has good continuity.The edge web has a large temperature difference,the maximum difference can reach 3.25℃.(2)The finite element numerical simulation of the temperature field of the steel-concrete composite beam with PK section without pavement in the construction stage was carried out.The numerical calculation is in good agreement with the test results.Based on the meteorological parameters of sunny days in summer and cloudy weather with long sunshine hours,the vertical maximum positive temperature difference data of composite beams are obtained through finite element model calculation.Statistical analysis found that the maximum vertical positive temperature difference in this type of weather obeyed the generalized extreme value distribution.Taking the 50-year return period as the standard,the standard value of vertical positive temperature difference of composite beams in Jiangmen area is 14.946℃.The exponential function is used to describe the vertical temperature gradient distribution curve of the composite beam.The vertical positive temperature gradient model of the unpaved PK section steel-concrete composite girder in the construction stage of the main bridge of Yinzhou Lake Bridge is obtained as:Tv=14.946e-12.3y.(3)Based on the three meteorological parameters of latitude,altitude and the daily temperature difference corresponding to the annual maximum temperature,a prediction formula for the standard value of the vertical positive temperature difference of the composite beam is proposed.According to the prediction results of the standard value of the vertical positive temperature difference of composite beams in 235 cities across the country,China is divided into 3 regions for temperature difference values.The values for each zone are 14℃,16℃ and 18℃,respectively.The proposed vertical positive temperature difference standard value prediction formula and temperature difference value division are suitable for composite beams with unpaved PK section.(4)For the PK section composite beam without the tuyere structure on the side,the maximum daily lateral temperature difference of the roof reaches 10℃ and the maximum daily lateral temperature difference of the bottom plate reaches 8℃.They all exceed the provisions of the current Chinese code for the transverse gradient temperature to be 4℃ for concrete box girder and 3℃ for steel box girder.The vertical maximum positive temperature difference at the outer web is significantly larger than that at the inner web,and the maximum difference between the two can reach 6.75℃.In the sunshine temperature field,attention should be paid to its transverse temperature gradient.The vertical temperature gradients at the outer and inner webs are calculated separately.(5)In the working condition of the full bridge in the construction stage,under the action of vertical positive gradient temperature determined in this paper and uniform temperature rise,the maximum tensile stress of the lower edge of the concrete roof section can reach 0.73MPa,and the maximum upper arch can reach 2.3cm.After the full bridge is closed,the deflection and stress of the composite beam caused by the temperature effect have a great influence on the subsequent cable adjustment of the full bridge.Based on the vertical temperature gradient mode and uniform temperature effect of the 100mm asphalt concrete paved composite beam specified in the specification,a combination of effects is carried out on the load action in the limit state of the load-carrying capacity of the bridge.The most unfavorable load effect combination of "dead load+lane+system cooling+positive gradient temperature" on the upper edge of the concrete roof section of the composite beam is obtained.The most unfavorable value of the upper edge of the section is 18.9 MPa compressive stress.