Abstract:

Abstract:Traditional tendon design methods for prestressed concrete (PC) continuous girder bridges are tedious since they obtain feasible solutions based on trial calculation, and the existing optimization methods that can obtain the optimal solution have deficiencies regarding structural stress. In this study, based on research on the refined bridge design conducted in the Department of Bridge Engineering at Tongji University in recent years, a stress index-based tendon optimization method for PC continuous girder bridges is pro-posed. First, various tendon layouts are summarized, and a reasonable tendon layout is selected. Then, a mathematical tendon optimization model is established. After meeting the specifications and construction feasibility requirements, a genetic algorithm is used to find the optimal solution. This method not only realizes tendon forward design but also obtains a satisfactory solution. Finally, this method is used to successfully optimize the tendons of a three-span PC continuous girder bridge, which verifies the ration-ality of the method.

Abstract:Cable structure is an important type of structural bearing system. With the increasing of span and height of modern engineering structure, the length of cable used in civil engineering is increasing, and its structural form becomes more and more complex. In this case, the dynamic analysis of cable structure has become the key to the structural design, service performance monitoring and maintenance, and vibration control. The existing cable dynamic analysis theory can only consider the influence of some design parameters, or be suitable for cable systems with relatively simple structural forms, and difficult to balance analysis effi-ciency and accuracy and apply to the exact dynamic analysis of complex cable structures. Based on the dynamic stiffness method (DSM), this paper develops a set of exact dynamic analysis method for complex cable system; The effectiveness and applicability of this method are illustrated by taking naked cable system, composite cable system and multi-segment cable system with lateral supports as representatives. The main contributions and achievements are as follows: The exact solution of the frequency equation of small sagged cable considering bending stiffness, internal damping and additional cable force is presented; The dynamic modeling and solution of stay cables with double-sheathing anticorrosion system are given, and the influence of filling material on damping and frequency of the system is explored; Based on the DSM, the dynamic model of multi-segment cable system is established, and the corresponding dynamic solution scheme is proposed. According to this, the dynamic characteristics of the main cable of a suspension bridge are analyzed. The theoretical analysis results are in good agreement with the measured values and finite element solutions, which shows the accuracy of the proposed method. The cable dynamic analysis method proposed in this paper has high calculation accuracy and is easy to implement, which can provide theo-retical basis for the initial design and health monitoring of cable and cable structures in engineering.

Abstract:The cable saddle on top of pylon not only helps the main cable pass through the summit of design form, but also transmits the enormous force to the pylon. An imbedded cast iron cable saddle is going to be adopted for a single pylon and two span cable stayed bridge. A cast in situ concrete foundation, which is called a concrete mount in this context, bears the imbedded cable saddle underneath. Due to the cambered shape of the bottom face of this imbedded cable saddle, the local compressive stress distribution on the contact part with the concrete mount may not be uniform. The finite element method is used to investigate the feature of the local compressive behaviour for the concrete mount. According to the results, the reduction factor for nonuniform local compression is approximately 0.73. This cable saddle structure could meet the local compression bearing capacity via theoretical verification, and indirect reinforcement under local compressive pressure is recommended to keep the structure in good condition for the serviceability limit state.

Abstract:This paper mainly studies the mechanical properties of simply supported bridges of steel?concrete composite structures strengthened with externally prestressed CFRP plates. The introduction of the prestress of the CFRP plate from the support rods can not only apply prestress to the main beam but also provide an upward lifting force at the bottom end of the main beam to reduce the deflection of the original structure. Therefore, the CFRP board is prestressed by the support rods, which can improve the speed and efficiency of rein-forcement construction. The effects of the CFRP amount, prestress size, support rods amount and other parameters on the stiffness and bearing capacity of composite beams were studied by a static test of the scaled model. In the flexural test of the tensioned combination beam, by increasing the prestressing level and the number of CFRP plates, the flexural moment of inertia of the combination beam section was effectively improved, the reinforcement effect on the yield bearing capacity and ultimate flexural bearing capacity of the combination beam was obvious, and the reinforced specimens still had good ductility. For the third com-bination beam, a CFRP plate with a 15% prestressing level and 3 mm thickness was used for reinforcement. The ultimate load carrying capacity of the combined beam was increased by 47.9%; the yield load of the lower flange was increased by 39.8%; and the stiffness in the elastic phase was increased by 21.66%.

Abstract:With the development of modern long-span cable-stayed bridges, due to the parallel strand cable (PSC) being assembled on-site strand by strand, which has the advantages such as no need for large-scale equipment for cable-making, delivery, hoisting, traction, tensioning, and the corrosion protection of the cable is excellent, it is more and more favored by designers. As load-bearing components, the stay cables are known as the life cable of the cable-stayed bridge. Its reliability and durability are the key factors that determine the safety and the service life of the cable-stayed bridge. In accordance with the requirements specified in international recommendations, in-depth research has been carried out on cable fatigue, anti-corrosion, and vibration control to optimize OVM250 PSC system. All research results have been successfully applied to cable stayed bridge projects.

Abstract:The main bridge of Quzhou Academy Bridge is a V-shaped rigid frame bridge with a hanging hole, the span arrangement is 75 m+150 m+75 m=300 m, the middle span hanging hole was provided with a 60 m steel box girder, and the V-leg structure and the main beam are all prestressed concrete box girders with variable height. Due to the need for bridge landscapes and pedestrian viewing platforms, the large extension arc V-leg structure extends 6 m to each side of the bridge deck, and the total width is 41 m. It was necessary to consider the stress effect of the shell in the longitudinal and transverse directions. The stress and deformation of the shell in two directions are analyzed by using the finite element method solid model, and the difference between the solid model and the frame model is compared in detail. Finally, the overall structure was analyzed and checked in the modified simplified frame finite element model.

Abstract:The Nanxi (Xianyuan) Yangtze River Bridge in Yibin is a composite beam cable-stayed bridge with twin towers and double cable planes and a main span of 572 m. The superstructure is erected by the assembly method. In order to ensure the precise installation and control of internal forces for steel girders and bridge deck slabs of composite beams while also considering the construction efficiency of composite beams, a control method for the installation and erection of the superstructure has been proposed. This method is based on optimizing the internal force and geometric states of segments throughout the entire process, achieved by establishing finite element calculation models for both the full bridge and segmented sections and combining these with comparative studies of on-site monitoring data. With the installation stress and precision of composite beams properly controlled, construction efficiency has been enhanced through the optimization of the pouring process for wet joints between steel girders and concrete bridge deck slabs, as well as the tensioning process for stay cables. The equivalent tension method is applied to the tension process of the stay cable, thus ensuring the uniformity of the cable force of the steel strand. The relevant conclusions are applicable to the same type of composite girder cable-stayed bridge erection construction.

Abstract:The Tuojiang Bridge of Jinjianren Expressway Phase II is located in Jianyang City and the Eastern New District of Chengdu, all the section length is 4.3 km with a total construction and installation cost of about 1.74 billion yuan. The road is classed as both a first-class highway and an urban expressway, with a design speed of 80 km/h for the main line and 40 km/h for the auxiliary lanes. Tongji University Architectural Design (Group) Co., LTD designed the main bridge which is an urban landscape bridge with a length of 963 m. The main bridge adopts 45+185+238+45m single-tower double-cable-plane cable-stayed span layout, and the approach bridge adopts prestressed small box girder structure.

Abstract: