Stress State Analysis Of Tower And Beam Of Arch Pylon Concrete Cable-Stayed Bridge In Construction Stage

Arch pylon concrete cable-stayed bridge,as a new type of pylon cable-stayed bridge structure,is difficult to control its linearity and internal force because the pylon limbs are inclined inward in the process of bridge tower construction.The transverse width of the main beam is large,and there is an obvious shear lag effect during the construction of the main beam.In addition,with the system transformation from cantilever to bridge,the stress state of the structure has changed significantly,and the selection of closure scheme is particularly important.Therefore,taking a cable-stayed bridge under construction as the background,this paper studies the stress state of the tower and beam of the arch tower concrete cable-stayed bridge in the construction stage.The main research contents are as follows:(1)By analyzing the location of the temporary cross brace of the bridge tower,the top thrust of the cross brace,the removal sequence of the cross brace and the pre deflection of the bridge tower,the Arch Tower alignment and internal force control are studied,and the influence of temperature effect is analyzed.The analysis results show that the position of cross brace and the magnitude of jacking force need to be determined by the principle of double control of stress and alignment;The setting of cross bracing,the application of jacking force and the setting of pre deflection can effectively reduce the tower limb displacement and tensile stress in the process of bridge tower construction.Combined with the measured data,the effectiveness of the measures is proved;Under the action of temperature gradient,the deformation and internal force of tower legs on both sides of the bridge tower are different;During the construction of the main beam,with the tensioning of the stay cable,the displacement of the tower limb first decreases and then increases,and the maximum displacement increases by 1.46 times compared with that without the construction of the main beam.The maximum tensile stress at the inner and outer parts of the tower limb also increases,which is 0.75 times and 1.41 times higher than that when the main beam is not constructed.(2)The solid finite element analysis model is established to analyze the whole construction process of the largest double cantilever beam section and the stress distribution of the prestressed concrete main beam,and the variation law of shear lag of the main beam is obtained.The analysis results show that during the cantilever construction of the back fulcrum hanging basket,the stress and shear lag coefficient of the top and bottom plates of the main beam near the tower change little,and the roof of nearly 1/2 span and nearly 3/4 span show complex alternating characteristics of positive and negative shear lag;Concrete pouring and cable tensioning are the main construction processes that affect the shear lag effect of the main beam;The tensioning of prestress can significantly reduce the shear lag effect of the beam section with 1/4 of the maximum cantilever span near the tensioning section,and has little effect on the beam section far away from the tensioning section;Compared with the stress of the main beam calculated according to the plane section assumption of the elementary beam theory,considering the shear lag effect of the main beam,it has the greatest impact on the stress near the flange plate and the middle web of the top plate,the stress at both web plates of the bottom plate increases,and the stress at the middle of the bottom plate of the side box decreases.(3)In order to make the prestressed concrete cable-stayed bridge reach the target completion state,the closure scheme of the main beam is optimized based on the stress-free state method,the influence of the closure temperature of the main beam is analyzed,and the closure temperature suggestions are given.The analysis results show that the closure scheme when the unstressed state of the closure section is close to the initial design value can be selected for the closure construction of the main beam;The stress free state of closure section is different,which mainly affects the alignment of main beam and bridge tower,and has little effect on the stress of upper and lower edges of main beam;By analyzing the alignment of the main beam,the alignment of the bridge tower and the stress of the upper and lower edges of the main beam,it is determined that the closure temperature of the main beam is better when it is close to 25℃,and the theoretical verification is carried out by comparing the non stress state of the closure section under each closure temperature.