Abstract:The long-span prestressed tension-string pipe beam is a new type of structure for transportation pipelines crossing rivers or trenches, with a span of up to 100. 150m. Taking a 100m span prestressed tensioned string pipe beam as prototype, a 1:15 scale model is designed, and the whole process of stress testing of the tensioned string pipe beam in the prestressed tension stage, the normal use stage and the ultimate bearing capacity stage is carried out for the first time in China. The nonlinear finite element simulation of the whole test process is carried out based on ANSYS, and combined with the uniform defect mode method and the cylindrical arc length method, the buckling analysis considering both the initial geometric defects and geometric nonlinearity is carried out. The experimental study and finite element analysis show that the half-span load is unfavorable to the prestressed tension-string pipe beam, and the overall deformation and upper string stress of the structure increase rapidly. The structure is more sensitive to out-of-plane geometric defects, and the critical buckling load under half-span load is slightly lower than that under full span load. The structure has reliable stability and large safety reserve, and the ultimate bearing capacity is 2.68 times of the design load. The calculated results of the finite element method agree well with the experimental results, which shows that the nonlinear finite element method used in this paper can simulate the whole process of the stress of the prestressed tension-string pipe beam. Finally, based on Rayleigh-Ritz method, the calculation formulas of deformation and internal force of prestressed tension-string pipe beam under elastic and elastoplastic conditions are derived.

Abstract:In order to obtain the flexural strength of external prestressed concrete beams, the ultimate stress of external prestressed tendons must be determined first. In the past half century, many scholars have conducted experiments and analysis on the ultimate stress of unbonded prestressed tendons in vitro or in vivo, but these researches mainly focus on steel and rarely on fiber composite materials (FRP). Based on the relevant experimental data, the difference and change of the ratio between the length of equivalent plastic zone and the neutral axis of the failure section are analyzed in the case of FRP and steel reinforcement. The analysis shows that for external prestressed concrete beams with FRP, this ratio is stable and can be a constant. However, this constant is different from that of the components with steel as external prestressing tendons. In this paper, the conversion relation between the length of equivalent plastic zone and the ratio of neutral axis of failure section is established when FRP and steel are prestressed in vitro respectively. On this basis, it is suggested that it can be applied to both simple supported beams and continuous beams. The calculation method of the ultimate stress of external prestressed FRP bars is suitable for both conventional external prestressed steel bars and non-conventional external prestressed FRP bars.

Abstract:In order to improve the durability of the cable, combined with the experience of product development and engineering application, the anticorrosion requirements of the cable system were put forward according to the fib2005, PTI2007 and CIP2002 international standard for the cable system, including the anticorrosion structure of the cable body and the cable anchor The sealing structure and watertight performance, surface anticorrosion of cable anchors and other links are studied, and the protection treatment in the construction and operation of the cable is required to ensure that the OVM250 steel strand cable system meets the requirements of the specification and the expectation of the service life of the project.

Abstract:Prestressed high-strength threaded steel bars are widely used in the construction of Bridges, grid buildings, docks, tunnels and dykes, etc. With the continuous development of building structures in our country, the installation of large structures and their components is also increasing, and the requirements for the strength and diameter of prestressed high-strength threaded steel bars are also increasing. This paper introduces the application of large-diameter high-strength threaded steel bar developed by Liuzhou Overwem Machinery Co., Ltd. in the full scale project test of Hong Kong-Zhuhai-Macao Bridge preset cap and the construction process of supporting anchor products. The application of high-strength threaded steel bars has promoted the technical progress of the steel industry and machinery manufacturing industry, and has great significance for the construction of Bridges and other fields at home and abroad, and has better economic benefits and far-reaching social benefits.

Abstract:Taking Jialingjiang Bridge of Chongqing Shuangbi as an example, the construction technology of parallel steel strand cable-stayed cable and the complex construction technology of single cable tension combined with front fulcrum hanging basket are introduced.

Abstract:In order to realize the cyclone milling of large pitch T-thread (the outer diameter of the workpiece is greater than 200mm, the pitch is greater than 16mm), ensure the product processing accuracy, improve the tool life and production efficiency, a machine clamp tool is designed for cyclone milling a large number of large pitch T-thread products. Two sets of machine clamping tools are designed for roughing and finishing respectively. The design structure of the clamping tool adopts the tool body parts that can be used many times and the blade that can be changed quickly. The left and right blades with wrong teeth are used in milling. The blade material is cemented carbide; By changing the corresponding parameters of the blade, the stress of the blade and the quality of the milling product can be improved, and the service life of the tool can be increased.