Determining The Reasonable Design State And Reasonable Construction State Of Complex Suspension Bridge

In last decades, there is trend towards longer span and lower safety margin for suspension bridge construction. Meanwhile self-anchored suspension bridge has developed rapidly and combined cable bridge becomes more and more popular Also the shape of the main cable extends to 3D and main beam varies in shape. Thus, based on two NSFs granted to supervisor and taking five typical complex suspension bridges as background engineering, some work has been conducted in this dissertation, including the determination of reasonable completion state, the cable construction control system, as well as the determination of the reasonable construction state which takes into account the multiple level non-linear impacts during construction period. This work has been performed on the general rule of "determining final state ahead of construction stage". The main works and results are as follows.1) On the determination of reasonable completion state for complex suspension bridge(1)According to the nature of slight impact between bridge completion state and construction process, a progressive model has been raised to determine the rational completion state., First, build the independent rigid support successive girder to obtain the initial force value of the suspension cable and the stress mix; Secondly, take the vertical component of hanger stress as known, and create a separate main cable model to pursue the shape-finding calculation; Thirdly, Crete a new girder model more in line with the actual (replacing the rigid supporting at anchor with vertical force in hanger) and adjust the vertical suspension force. Fourthly, with latest hanger stress, repeat the adjustment process until the cable and girder geometry shape under dead load meet the design requirement; Finally, by integrating results on the main cable, build the FEM of full bridge one the basis of main beam model,. Check the effect under variable loading and modify the cable force accordingly. Repeat these processes until achieve the rational state under dead and live load.(2)It was found that the coordinate of the suspension point of the spatial main cable shelf-anchoring bridge were determined by the force balance of the main cable and the suspension cable, rather than the experiences. Then, the spatial main cable shape design theory, method and flow chart were proposed. In this new theory, the key part was the adjustments of the horizontal component force of the suspension cable after the elevation of the main span were determined, after which the stress design was determined when the differential value between two consequential steps was below the predefined value.(3)A new bridge finished state determination named "two steps in one"was proposed after analyzing the mechanical characteristics of the triple tower middle stayed cable suspension combination bridge. In this new method, the bridge finished state were optimized in both the design stage and construction state synchronously, which could make sure both the construction state and bridge finished state were all reasonable.2) On cable construction control systemThe approaches to control the predefined bias of the precision demand and the side span main cable design control were discussed. After this, the necessity and the developing scheme of the shape calculation of cable shape for the ground anchored suspension bridge were analyzed. At last, the anchor span stress controls value determination and that when the temperature difference between day and night was big.3) On the determination of the reasonable construction state which takes into account the impact of multiple level non-linear during construction period.(1)A new concept was proposed, which considered that the simulation results of the one-time-frame-setting method for construction of self-anchored suspension bridges are similar to that of the ordered installation method. The modeling, calculation and results post-processing methods of the ANSYS simulation for the construction of the suspension bridges are given. The shortcomings of the ANSYS and Midas Civil for the simulation of the suspension bridge construction simulation were also pointed out.(2)A saddle-cable unit was proposed based on precise elastic catenary theory, considering the arcs tangent point between the main cable and saddle arcs, while integrating the simulation of saddle pushing, without considering the flexural rigidity of the tower node. On this foundation, a software based on Analytical method and finite element method was developed, which involved the existing mature Space truss finite element theory of Multiple nonlinear static overall analysis for complex suspension bridges, considering multiple non-linear factors, such as geometric nonlinearity, shrinkage and creep, saddle pushing, correction of the tangent point of the main cable saddle, multiple tension of the suspension cable and stay cable. This software was evaluated by the real case study.(3)The construction organization of four bridges was optimized, among which are three large-span suspension bridges and one complex three-tower bridge containing both suspension system at side span and cable stayed system at central span.First, in order to solve the problem of setting temporary support anchoring device and the temporary suspension cable anchoring device, a new system transformation is proposed, in which the stress design of the first permanent suspension cable near the splay sets is full filled, followed by the splay sets and the permanent suspension cable of the main tower.Second, a new cable adjust concept was proposed for the double tower lateral inclination space main cable self-anchored suspension bridge, which determines the stress of the permanent suspension cable near the temporal cable in order to overcome the shortcoming of the deficiency of the allowable value of cable force. This forms a new system transformation approach for self-anchored suspension bridge after calculation optimization, which does not need actively relax the temporal cable.Third, a system transformation optimization method named "middle and two sides Synchronization, step by step design" was proposed for the plane main cable double tower three-span self-anchored suspension bridge.Lastly, a construction scheme named "first girder, second cable" was proposed for the triple tower middle stayed cable suspension combination bridge, which decrease the cost and increase the safety during removing the temporal devices compared with the normal construction scheme.For the construction and stress design of complex suspension combination bridges, a new conception was proposed, which consider the worst cases not only during the design stage but also at construction stage the latter could be the main factor.