Analysis Of Static Behavior And Dynamic Property For Asymmetry Suspension Bridge

With the development of the highway to the mountain area, the suspension bridge is always the best preference because of its long-span with strong spanning capacity and beautiful appearance.However, in order to adapt to the special engineering environment, such as large span and deep trench V, the suspension bridge with main cables, anchorages both sides and side span asymmetry appears. Therefore, to search the mechanical properties of asymmetry suspension bridges, the effect of asymmetry main cables, anchorages both sides and side span on static behavior and dynamic property of suspension bridge have been analyzed based on practicsl asymmetry suspension bridge. The main research contents and conclusions of the paper are listed as following.(1) Static calculation formula for main cable shape of parabola and catenary of asymmetry suspension bridge were derived based on the theoretical analysis methods. The approximate calculation method and the finite element method(FEM) were used to calculate the stressed cable length and unstressed cable length of anchor, side, and middle span with different asymmetric sensitivity parameters. The stressed cable length and unstressed cable cable length of middle span have grown up with asymmetric sensitivity parameters exponential rate. In addition, calculation method on saddle pushing of asymmetry suspension bridge was studied based on energy method.Formula for the maximum allowable displacement of main tower was derived from Rayleigh-Ritz method. The pushing method of the main cable saddle was optimized from the perspective of both displacement of main tower top and stress at tower bottom. Finally, accuracy of the proposed formula was verified by FEM.The results show that asymmetry from suspension bridge leads to different pishing displacement of the main cable saddle on both sides.The error between the result from proposed formula and that from FEM is 3.4%, and the error from processes considering and without considering the effects of P- ? on the main tower is 4.6%. The maximum allowable displacement of the tower keeps increasing with the lifting of stiffening girders, and the increase amplitude can reach 19.9%. Meanwhile, the pushing values and time interval should be gradually increased and pushing times should be reduced, which resolves problems during pushing the saddle of the asymmetry suspension bridge and optimizes stress state of the main tower.(2) Based on the suspension bridge of anchorage asymmetry both sides, the differences between the tunnel-type anchorage and the gravity anchorage were analyzed in terms of stress mechanism, and rock displacement and stress state of tunnel-type anchorage zones in process of excavating, backfilling, prestressing and applying main cable tension of Puli Bridge have been analyzed by numerical simulation method of the finite difference software FLAC3 D. The trend chart of rock displacement with the change of main cable was given. Rock displacement gradually increases with the increase of cable force, and the slope is also increasing, which shows that the changing rule between the rock displacement and cable force is non-linear changes. When the main cable force exerted by the anchoring concrete-plug reaches 7.5 times of the design cable force, the net increase of the rock displacement is 1.96 times of the displacement from design cable force.(3) Since the estimation formula of vertical and torsional fundamental frequency in Chinese wind-resistant design specification for highway bridges was derived based on the ordinary suspension bridges,it is unavailable in estimating the fundamental frequency of asymmetry suspension bridge without taking these design parameters of asymmetry main cables and side span into account. In order to calculate vibration frequencies of asymmetry suspension bridge conveniently and rapidly, frequency formulas for 1st symmetric vertical vibration of suspension bridge with asymmetry main cables were derived under both cases that considering and not considering the influence of side-cable and tower stiffness on vibration frequencies based on Rayleigh,s method.Asymmetric structure influencing factors in revised standard formulas and that considering the influence of side-cable and tower stiffness were both put forward. Formula for influencing factors of side-cable and tower stiffness on vibration frequency was also given, and frequency formulas for 1st vertical and torsional vibration were derived based on the Rayleigh,s method. As for 1st symmetric vertical and torsional vibration, asymmetric structure influencing factors for correction of code formula were put forward, and formula for crankle ratio of the fundamental frequency was also derived, and the application condition was discussed. Finally, the accuracy of the proposed formulas was examined by FEM. The results show that when calculating vertical vibration frequencies of asymmetry suspension bridge, the influence of side-cable and tower stiffness should not be ignored, and the result of calculated by proposed formulas considering side-cable and tower stiffness is much agreed with that calculated by the FEM.The error is 3.3%,which meets requirements of accuracy for projects.In addition,1st anti-symmetric vertical and torsional vibration of asymmetry suspension bridge is free from the influence of asymmetry structure parameter. While for 1st symmetric vertical and torsional vibration, the decreasing range of fundamental frequency is obviously more significant when the structure sensitivity parameter exceeds 0.1. In this paper, the fact was found that there wre differences of vibration frequency between the asymmetry suspension bridge and symmetry suspension bridge with high-end or low-end support by FEM. The sensibility of the dynamic characteristics of the asymmetric suspension bridge to the variation of the structural parameters was analyzed.The effect of parameters including the rise-span ratio of asymmetric structure, sensitivity parameters of asymmetric structure, the flexural rigidity of the main tower and flexural rigidity of girder rigidity on dynamic characteristics of the asymmetric suspension bridge were studied. The sensitivity of the dynamic characteristics of the asymmetric suspension bridge with different parameters was obtained. The relationship between the partial parameters and the vibration fundamental frequency of the asymmetric suspension bridge was fitted.(4) The dynamic property of three span suspension bridge with side span asymmetry was studied by Rayleigh-Ritz method. Frequency formulas for 1st vertical and torsional vibration were derived.The applicability and universality of the formulas was discussed, and the accuracy of the proposed formula was verified by FEM.(5) Mechanical properties of the asymmetry suspension bridge were analyzed based on dynamic load test and long-term monitoring test. Fundamental frequency and modal parameters of structure was obtained by practical bridge. The theoretical value and experimental value were compared and analyzed,and the error of them was discuseed.Settlement and displacement of slope surface of tunnel-type anchorage, deformation of tunnel-type anchorage, stress of anchoring concrete-plug and surrounding rock of Puli Bridge have been studied by long-term monitoring method. Safety and stability of rock mass and surrounding rock from tunnel-type anchorage was analyzed, which can provide the basis for decision-making in design and construction.In summary, the error between vibration fundamental frequencies of asymmetry suspension bridge calculated by the proposed method and FEM can meet with the requirement of design phase, which indicates that proposed formulas can be applied to guide the schematic design and preliminary design of asymmetry suspension bridge.Study on numerical simulation of tunnel-type anchorage and long-term monitoring data can provide a decision-making basis for the design and construction of tunnel-type anchorage.