Analysis Of Temperature Field And Temperature Effect Of Pipeline Bridge Structure Under Thermal Pipeline Burst

When urban thermal pipelines cross large-span rivers,water main canals,highways,and valleys,pipeline bridges are usually used.Due to the corrosion and aging of thermal pipelines,there is a risk of leakage.The mechanical properties are affected to varying degrees.Therefore,studying the variation law of the temperature field and stress field of the pipeline bridge structure under the condition of thermal pipeline burst has theoretical research significance and engineering application value for the design and safe operation of the pipeline bridge structure.This paper has taken a box-section pipeline bridge spanning the main canal of the South-to-North Water Transfer Project as the research object,and has used ANSYS finite element analysis software to analyze the temperature of the upper structure of the pipeline bridge under different pipe burst positions,pipe valve closing time,pipe burst water temperature,and atmospheric temperature.The distribution law of the field and stress provides a reference for the optimal design of the pipeline bridge.The main work and conclusions of this paper are as follows:(1)ANASYS finite element analysis software as well as the Workbench platform have been used to establish a finite element model of constant cross-section box girder.The hot water flow thermo-solid coupling,thermal parameters and boundary conditions have been settled in the model.A transient simulation of the energy exchange in the process of hot water flow crossing the surface of the box girder The results have showed that there have been heat exchanges between the hot water flow and box girder as well as the air,causing temperature decrease to the hot water flow and uneven temperature distribution on the surface of the box girder.Therefore,the temperature gradually decreased along the hot water drop point to the surrounding.Meanwhile,there is a hysteresis between the change of the surface and internal temperature decreases.(2)The parameter sensitivity of the temperature field distribution of the box girder is studied by taking the initial temperature of hot water,the atmospheric temperature and the closing time of the pipeline valve as parameters.The calculation and analysis have showed that the highest temperature on the surface of the box girder occured when the water flow of the pipeline was completely cut off.With the increase of the closing time of the pipeline valve,the depth of the internal temperature rise of the box girder increases.The greater the variation of the internal temperature of the beam was,the greater the temperature difference between the inside and outside of the box girder,and the greater the variation of the internal temperature of the box girder.(3)Based on the analysis results of the above box girder temperature field,the initial temperature and atmospheric temperature of hot water in the burst pipe were selected,and a pipeline bridge spanning the main canal of the South-to-North Water Transfer Project was taken as the research object,and a 72+125+72m span variable cross-section box girder flow heat was established.The solid coupling model is used to simulate the temperature stress distribution law and deformation law of the box girder.The results show that due to the large temperature difference between the inside and outside of the box girder,the tensile and compressive stress generated by the box girder is also larger,and the longitudinal and lateral stress changes on the inner and outer surfaces of the roof are much larger than the vertical stress.(4)When the self-weight,pre-stress,pipeline load,and temperature load act together,four different pipe burst positions have been set up to analysis.The results show that the pipe burst position has a great influence on the stress on the upper edge of the pipeline bridge,and the maximum compressive stress appears at the position of the pipe burst.The pipe burst position has little effect to the stress on the lower edge of the pipeline bridge.Before and after the valve is closed,the upward vertical displacement caused by the temperature effect and the pipe unloading effect will offset the downward vertical displacement of part of the pipeline bridge under normal operation.The maximum vertical displacement after the valve is closed is about 1/6 of the vertical displacement of the pipeline bridge in the normal operating state.