Research On Construction Control Key Technology Of Multi-pylon And Spatial Cable-stayed Bridges

Multi-pylon and spatial cable-stayed bridge are gaining more and more popularity for its beautiful structure geometry, high adaptability tonavigation and topography conditions, good torsional and wind resistance capability, and so on. Although many studies such as on its structure system, stiffness improving measures and design calculation have been made, research on multi-pylon and spatial cable-stayed bridge’s construction and construction control are relatively under-researched and many problems are worth further research and deserve improvement.Taking Jiashao Bridge, a 6-tower spatial cable-stayed bridge, and Maanshan Bridge, a 3-tower spatial cable-stayed bridge, as project background, this thesis studies a series of construction control questions, including determining rational construction and completion state, calculating spatial 4-plane stay-cables force, parameter analysis of multi-pylon and spatial cable-stayed bridge, steel box-girder’s local stress caused by construction temporary loading, temperature field of steel box-girder without pavement, etc. The main results are as follows:(1) Aiming at the shortcomings that currently there is no clause on solar thermal gradient for steel box girder without pavement and concrete section of Pasco-Kennewick type in specifications for highway bridges and culverts in China and a heavy work would be invovled to determine it with measurement, a vertical solar temperature gradient is established through numerical calculation and on-site test of steel box girder in Jiangdong bridge and concrete girder in Maanshan bridge. t. When the temperature field is measured at the scene of Jiangdong Bridge, the calculation values coincide better with the measured values. And sensitivity analysis has been carried out to study the effects of various parameters on the temperature field. And it may be widely applied to determine solar temperature gradient in the steel box girder without pavement and Pasco-Kennewick type concrete girder in China. Also it had been verified through the on-stie test of steel box girder solar temperature gradient in Dongsha Bridge,The study shows that the absorptivity have the most significant effect on temperature distribution, while wind speed little. The vertical temperature gradient proposed here has a strong influence on the stress and geometry configuration of steel box girder without pavement.(2) To counter the deficiency of massive calculation and unclosed property associated with traditional approach, this paper presents a new method of two-in-one for determining rational construction and completion state of cable stayed bridges, The basic thought is as follows:according to the allowance range of governing parameters set by codes and designer, a initial value of cable force is determined by utilizing dead load balance approach under structure self-weight, structure stress and deviation of pylon top Then a forward iterative method is used to determine the initial and the adjustment amount of cable force, making structure internal force meet the design requirements under various construction condition, and ensuring the stress under load combination of action effects not only meet the design requirements but also have some safety margin.(3) Enough safety stock need to be taken during determining rational state to create conditions for construction control of cable force and linear adjustment; In addition to setting the pre-camber along the longitudinal direction, transverse pre-camber is worth consideration for wide box girder in construction. Concerning cable force lateral distribution in 4-plane cable-stayed bridges with twin girders connected via cross beam, on the basis of mechanical principal, statical analysis along the transverse direction of a single girder’s construction segment is performed. By introducing the torque balance equation, formulas on the ratio of internal and external cable force is deduced for 4-plane cable system in both the initial tensioning and the completion state. By employing these formulas to calculate the cable force ratio for Jiashao bridge during construction and after completion resectively, it shows that the difference is litter. Therefore the ratio at completion state may refer to the value at construction phase. Also analysis on influence factor indicates that:the weight of steel box girder plays a stronger role as weight parameter, and of geometry parameters, the horizontal distance between deck traveler and shear center along transverse direction pose a heavier influence.(4) FEM-based parameters sensitivity analysis indicates that:to meet construction control requirement, construction precision and control standards stricter than bridge code requirements should be set on following three aspects such as the cable force difference between mid-span and side-span, deck and wearing surface thickness of multi-pylon and spatial cable-stayed bridge; Meanwhile calculation results on construction sequence suggests that:all processes demonstrated in this paper, except for the demolition time of deck traveler on side span, shall be fixed before girder erection.(5) Based on the energy variational principle, taking into account the normal stress equilibrium condition in cross section and the influence of shear deformation, a new shear lag warping displacement function including parameter m is established for box girders. In this section, the calculated mean square errors of stress and deflection ware taken as standards to analyze the adaptabilities of the new functions with different parameter m. The results state that the quadratic function is more accurate. By comparing the calculated stresses in typical sections, it is further analyzed on the accuracy and adaptability of the new function (m=2). When trying to determine the stress of the exterior extreme of the flange in a simply supported box girder under concentrated load, there is a certain deviation in the calculation. For that deviation, by stress curve fitting, a new improved formula was obtained. Meanwhile, the stresses and deflections calculated with the newly established shear lag warping displacement function and the basic function respectively were compared to prove its validity and high calculation accuracy.(6) In view of the fact that the temporary load during construction is even larger than the design load under service state, mechanical response of steel box girder is analyzed for construction temporary load like deck traveler. And the critical case is identified in which structure is high prone to overstressing and buckling. Suggestion of large construction temporary load should be listed as one of the actions in "bridge and culvert general design code" is proposed, as well as much importance should be attached to the strength and stability verification during construction.