Study On Hoop Stress System Of The Tower Wall At The Anchorage Zone Of Cable-stayed Bridge Cable Bent Tower

The cable bent tower is a key part for controlling the design and construction of the long span cable-stayed bridge,where hoop pre-stressing bundled bars are needed setting to withstand the strong pulling stress engendered by the cable force,and the concrete is under the complex three- dimensional stress status.The paper studies the hoop stress system of the tower wall at the tip tower where the horizontal stress is maximal,relying on the study on the Songhuajiang Sifangtai cable-stayed bridge of Harbin surrounding highway.There are three aspects of the study:(1) experimental study on stretching elongation of large-tonnage and small-radius hoop pre-stressed bundled bars;(2)analysis and evaluation of the hoop pre-stress effect of tower wall through the comparison between the experiment and the FEM analysis result of full-scale segmental model;(3)Optimum arrangement for pre-stress bundled bars.The pre-stressed bar construction craft experiment is taken on the tower anchorage zone. According to the data from the experiment,the plastic corrugated pipes' warp factors k and friction factors/t are got by least square method and regression analysis.The paper analyzes and discusses the reason why the stretching elongation of pre-stressed bundled bars is bigger than that in the General Code for Construction of Highway Bridges and Culverts (JIJ041—2000).Under the small radius and large tonnage status,the stretching elongation of pre-stressed bundled bars is composed by four parts:the normal elastic extension,the extension caused by the differences of the restrained states, the geometry extension caused by radial compress and the movement of the bundled bars' center of gravity,and the extension caused by pipe breakage and the bend preliminary stress.The theoretic calculation formula of extension based on qualitative analysis is a helpful supplement to pre-stressed bundle bars extension calculation based on statistics of the General Code.FEM analysis is done on the hoop pre-stress effect of tower wall combined with the tower segmental model experiment.From the comparison between the analysis and the experiment,when the tower is under pre-stressed stage and before concrete corruption,the actual test value is almost equal to computer imitation,and taking the bundled bars as the center of the tower,the inside stress is larger than the outside, presenting belt.distributing character.Under the pre-stress and 14000kN cable force statuses respectively, the tower stresses distribute even and the distortions of the two statuses reverse, which show that the hoop stress assignment is suitable and its effect is prominent.Because of the limitation of the tower structure,the rational assignment of pre-stressed bundled bars is special and the optimum is to make sure the number of pre-stressed steels in every kind of bundled bar.After optimized,the number ofpre-stressed steels in the bundled bars from NI-N4 is 11,8,5,6 respectively,when the bearing capacity performance is the best.