Study On The Structural Behaviors Of The Cable-Stayed Bridge With United Twin-Pylons And Separate Twin-Decks And Model Test On The United Twin-Pylons

With the increase of traffic volume, bridges are designed with more and more wide decks, a kind of novel twin-deck bridge emerges as the times require. With spacious visual effect and good driving conditions, the twin-deck bridge gradually wins many people's good graces. The number of twin-deck bridges built at home and abroad gradually increases day by day. Most twin-deck bridges are two parallel structures, which are in independent force state except for aerodynamic interference effects. Yongjiang super-large bridge being built in Ningbo is a twin-deck cable-stayed one, but twin pylons of separate twin-decks are transversely joined into a monolithic one. The forcing states in twin bridges are mutually transferred through the joint part of the pylon. Twin bridges are in coupling force state. The working state and the safe reserve of the united twin-pylons have attracted engineers'attention. On the basis of collecting and studying correlative information at home and abroad, taking Yongjiang super-large bridge as an example, the structural behavior of cable-stayed bridges with separate twin-decks and united twin-pylons is studied and model test study on the united twin-pylons is made. The main research work is as follows:1. The structure state variables change with the construction stages going on, The variables can be expressed as the functions of cable forces and construction camber. The functions are derived in detail by considering the effect of geometric nonlinearity and creep. On the basis of the functions, a mathematical programming model for cable forces optimization in the cantilever construction stages of cable-stayed bridges is established, and the optimization program method is developed by the multi-objective, multi-restriction optimization algorithm using MATLAB program language. The command file about the simulation analysis for the cantilever construction stages of cable-stayed bridges is programmed on the basis of the development tool APDL language in ANSYS, which makes simulation analysis with a rule and simple. The linear and nonlinear calculation results are simply compared in the construction stages and the finished stage.2. In view of the coupling force state of twin bridges, quantitative analysis of the interaction degree of their force state is performed. A series of parameters extension analysis is carried out with different stiffness of the joint part and different lengths of the joint zone in order to study the parameters'effects on the interaction degree of twin bridges.3. Whereas aerostatic coefficients and wind loads specified in domestic codes are only in view of bridges with one deck,the aerostatic coefficients of two separate decks in Yongjiang super-large bridge are numerically simulated using the FLOTRAN CAD module in ANSYS. The stability in static wind and dynamic characteristics between the cable-stayed bridge with separate twin-decks and united twin-pylons and the one with single deck alone are compared.4. Taking the Yongjiang super-large bridge in Ningbo as an example, model test study on united twin-pylons is done. In order to optimally determine the assigning positions of stayed-cables, the number of stayed-cables and cable forces in the test, mathematical model and numerical programs for the least cables are developed. On the premise of meeting target state, assigning positions and corresponding cable forces are optimally determined according to the principle of minimal number of stayed-cables. Thus, at the same time of achieving the desired goal, the rate of utilization of stayed-cables is increased and the resource cost is reduced.5. Structural behaviors of united twin-pylons are studied in the model test. Displacements, stresses in control sections and cable forces are measured. The measured and the calculated results agree well. The rationality and feasibility of the cable forces optimization method for the minimal number of stayed-cables is verified by the test results. The mutual influence among stayed-cables, especially among those between different pylons in the united twin-pylons are made clear. Structural behaviors of united twin-pylons in the construction stages and the finished stage are shown in the test. Finally, the ultimate bearing capacity is tested and it shows a high coefficient of safety for the united twin-pylons. The model test results show that the cable-stayed. bridge with twin-united pylons and twin separate girders is feasible.