Theoretical Analysis And Test Study On Diagonal Belly Poles External Prestressed Cable Structures

The best advantages of prestressed reinforcement technology are that the collaborative work between new and old structure start at the same time of the strengthening completion. The external prestress is one of the important branch of post-tensioned prestressing system,which is developed rapidly in recent years and being used widely in the fields of building and bridge structures because of the merits such as convenient construction, economizing material and convenient maintenance, etc.Because of the slippage and deformation inharmony between external prestress bar and reinforced member, the strain of external prestress bar after loading is not equal to the strain of corresponding concrete sections, and the carrying capacity calculation of structure member is not suitable for the plane surface assumption theory. There are significant diffenrences of calculation results using different analysis methord and various theory assumption about the calculation of external prestress bar stress increment under normal loading.The cable is applied to bridge structural system originally, a distinctive feature of cable is the smaller length deformation and the larger deck structure transform, which can be neglected as far as the deformation of cable length are concerned, and there is a theory of invariant cable length. The feature of external prestressed cable structure in building structure is the larger cable length deformation and the smaller transform of original structure and the length deformation can not be ignored. The invariant cable length basic assumption of original theory is not suitable for analysis and calculation of the external prestressed cable structure.A tilted belly poles cable structures external prestressed reinforcement technology is proposed on the basis of traditionally external prestressed reinforcement technology. The cable structures theoretical model is established and derived by taking the simply-supported beam reinforcement as the research object, the parameters of the reinforced composite structure system are basically assumed, the cable deformation increment and tension force formulas of the composite structure system are obtained. The paper modifies the unchanged cable length assumption in the calculation of the cable structures, which analyses the relations between deformation, tension force and the load, the results shows the cable structures figure is a part of the ellipse, the cable maximal horizontal tension force lies in the mid-span of the simply-supported beam, there is the minimal horizontal force in anchor point. Not only can such a stress characteristic fully develop the cable advantage of the high tensile capacity, but also it can decrease the unfavorable effects of cable horizontal force on the beam. Under the action of the radial uniform load, it shows the nonlinear relationship between the cable length incensement and deflection incensement. By means of iterative calculation,the precision is related to the magnitude of load-steps, the smaller load-steps, the higher precision, and the precision will be reduced on the contrary. The study of the paper provides theoretical references for the application of new technology.7 Unit Tests with ordinary spring were taken to simulate the prestressed cable. Vertical load was imposed on the cable, according to the variation of tilted belly pole members, load-steps and height span ratio. The deformation rule of the cable was studied by testing the characteristic values of cable, such as cable length, the maximum cable sag value, the maximum tension value.The results show that (other conditions are equal):(1) The larger the number of web member is, the more close the test result is to the theoretical analysis test;(2) The smaller height span ratio is, the more accurate the calculation results is;(3) The bigger height span is, the smaller the maximum tension value of cable is.The results can provide theoretical guide to the engineering.The tilted belly poles cable structures external prestressed reinforcement technology can be used in reinforcing horizontal members and the vertical elements, which would be applied more widely and easily in practical engineering.