Study On The Effect Of Sunshine Temperature Difference On Super High Pier Tower Of Multi Tower Cable-stayed Bridge

As a part of the long-span cable-stayed bridge,the pier tower is exposed to the outside environment all the year round,which is affected by the atmospheric temperature,sunshine radiation,sudden temperature rise and fall and annual temperature difference.Due to the poor thermal conductivity of concrete,the internal temperature of the bridge tower changes slowly,resulting in large temperature difference stress and displacement,which has a negative impact on the safety of the bridge structure.Multi tower cable-stayed bridge,especially super high pier multi tower cable-stayed bridge,its main components cable,tower and beam may be more significantly affected by temperature difference effect.However,the current code is lack of analysis regulations on the influence of daily temperature difference of super high pier tower,and the complexity of bridge tower and the whole structure of this kind of bridge,which makes it difficult to accurately calculate and evaluate its influence,so it is necessary to carry out relevant research combined with specific projects.This project is a super high pier three tower steel-concrete composite girder cable-stayed bridge in Guizhou mountainous area.The main tower is 332 m high,the height is the first in the world.The bridge tower is a diamond shaped space tower.From the bottom to the top,it changes from a monolithic pier to a four tower and two tower structure,and it is closed as a whole at the top of the tower.The special structure and the harsh temperature and climate conditions in the mountain area make the effect of sunshine temperature difference on the bridge tower in construction The impact of industrial and operational processes is of great concern.In the construction of bridge tower,the location of tower axis,the deformation of four tower legs and the change of stress after the closure of tower top need to be solved urgently.The main contents of this paper are as follows:(1)Research and summarize the characteristics of multi tower cable-stayed bridge,the research progress and results of temperature effect of bridge structure at home and abroad,and enumerate and analyze the domestic and foreign bridge accidents caused by temperature effect.(2)In this paper,the formation and classification of temperature field and three basic methods of solving temperature field are introduced.Combined with the relevant thermal theory,the thermodynamic boundary of the tower and three applicable calculation methods of solar radiation intensity,radiation heat transfer coefficient and convection heat transfer coefficient are analyzed.(3)Collect the meteorological data of Guizhou area and the temperature data of the bridge tower measured on site,analyze the distribution law of the temperature field of the bridge tower,fit the horizontal section,height direction and three-dimensional gradient temperature formula of the concrete bridge tower,and put forward the temperature field model suitable for the super high pier tower of the bridge.(4)An independent finite element model of concrete super high pier tower is established to analyze the influence of sunshine temperature difference on the deformation and internal stress of four pylons.The results show that in the temperature field,the displacement of each point along the bridge direction is greater than the displacement of each point across the bridge direction;in summer and winter,the maximum tensile and compressive stress of the bridge tower is the same: the maximum transverse tensile stress occurs near the southeast of the bottom of the bridge tower,and the maximum transverse and vertical compressive stress occurs near the south of the tower and the pier body.(5)In this paper,a two-dimensional model of two limb tower column of concrete bridge tower is established for detailed analysis.Considering the mutual shielding effect between tower columns,the change of temperature and stress of tower column section is studied.It is concluded that the stress state of the section of two leg tower in summer is more unfavorable than that in winter.It is necessary to pay special attention to the weak stress areas such as chamfering and turning angle in the section of bridge tower.(6)The finite element software is used to establish the construction stage model and the whole bridge model.Firstly,the influence of temperature effect on the deflection of main girder and the cable force is analyzed;secondly,the deformation law of tower,cable and main girder under the action of sunshine temperature difference and the sensitivity of different parts of cable-stayed bridge under various temperature conditions are analyzed The influences of live load and five temperature effects on the deflection of main girder are compared.The analysis shows that different temperature effects have different influence on the mechanical parameters of each component of the bridge,and the maximum deflection of the main beam brought by five temperature effects is close to half of the influence of two lanes on the deflection of the main beam,which shows that the temperature effect cannot be ignored.(7)A series of adverse effects of sunshine temperature difference effect on concrete super high pier tower cable-stayed bridge are summarized,and several effective methods are listed to weaken or avoid the harm of sunshine temperature difference effect on bridge tower.The method of coating reflective insulation material is recommended.