| Suspension bridge analysis and computation have become increasingly refined in recent years, with even intensive analysis to examine on the changes of tangent point between the main cable and cable saddle resulted from cable saddle pushing. Such refined analysis, however, is mostly done on structures after completion. Structures under construction, especially in the process of hoisting and mounting stiffened girders, add to the complexity of analysis due to their unique characteristics. In this case, it is all the more necessary to conduct intensive analysis of the mechanical properties and seismic properties of the structures. With the use of refined finite element technology, the dissertation dissects the structural mechanical properties of main tower and main cable as the major components of suspension bridge as well as the seismic properties of suspension bridge at construction stage.The refined finite element analysis referred to in the dissertation lies largely in the adoption of high-precision elements to simulate the main components of the structure.First of all, the main power is simulated by fiber element model, which has similar computational precision but higher computational efficiency compared to 3D solid modeling. Furthermore, to better deal with the elastic-plastic analysis of appreciable issues with shear effects under complicated stress state, the dissertation builds on traditional fiber modeling theory and puts forward a fiber model that considers the effects of shearing deformation through Poisson ratio, and thus addresses the problem of significance difference between computational and experimental results of displacement of components with small length-width ratio. Comparison with experimental results finds that for such components, computational results of the fiber model which considers shearing deformation are 15% to 25% more precise than those of pure bending fiber model, and that the hysteresis loops obtained are more consistent with the shear-type components form features.Given the fact that main cables are curved after cabling is completed, spatial curved beam elements are used to simulate the main cables as the former fully considers the coupling effects of various types of internal forces and deformation. During study of previous works, it is found that the existing curved beam theories have drawbacks with geometrical equations under the circumstances of large displacement and big angles of rotation, and fail to actually take into account the coupling effects of various spatial internal forces. Therefore, studying the analytical theory under the circumstances of large displacement, big angles of rotation, and great curvature of curved bars will be not only of theoretical significance but also of practical engineering significance as it can be applied to the refined analysis of suspended bridges. In order to make up for the drawbacks of existing curved beam theories, with the use of mathematical tools including co-moving curvilinear coordinate representation and tensor analysis, the geometric equations, spatial two-directional bend-rotation coupled equilibrium differential equation, nonlinear virtual work equation and constitutive equation of arbitrary spatial beams under the circumstances of large displacement, big angles of rotation, and great curvature are systematically derived. The idea of straight beam element displacement component interpolation is improved to displacement vector interpolation to establish displacement field that applies to any curve types of Total Lagrangian (TL) and Updated Lagrangian (UL) incremental finite element formulations for spatial curved beams. Comparison of calculation results indicates that the precision with curved beam elements is noticeably higher than that with segmented straight beam elements. Typically, it takes only one fifth as many curved beam elements to achieve the same level of calculation precision as it takes straight beam elements. Method of forming the consistent mass matrix for curved beam elements is given. In addition, static condensation method is improved and the generalized static condensation.Existing commercial software cannot be applied to conduct analysis due to use of highly precise elements from independent research. The authors'research necessitates a set of purpose-built and proprietary analytical software. Building on the foregoing theoretical preparation, software MockCool is developed as the first phase of work. MockCool is featured with its capabilities of fiber model analysis considering shear deformation, analysis of spatial curved beam elements with large deformation, automatic conversion between and loading of disassembled elements and (restraint) internal forces, and dealing with boundaries with improved large mass method, etc. Comparison of computational results with MIDAS and literature results (experimental results), the accuracy and rationality of MockCool's computational results are verified.Based on the foregoing theoretical preparation and software development, using the independently developed software, a great quantity of computation and analysis are done specific to the characteristics of suspension bridge under construction, and the structural mechanical properties of main cable and main tower, the two major components of a suspension bridge under construction.The bending stiffness of main cable after cabling is completed for long-span suspension bridge is indeed negligible. However, during hoisting of stiffened girders, does the bending stiffness of the main cable have any effect on the structural analysis at this point of time? How much effect? No one has been able to answer these questions as of now. In order to give a quantitative answer as to how much effect there is of the bending stiffness of a suspension bridge's main cable, numerical analysis takes the bending stiffness into consideration and analyzes bending stress parameters of main cable with different spans. Results are as follows: During hositing of stiffened girders, the secondary bending stress of the main cable of long-span suspension bridge peaks at 15% of the primary stress. The secondary bending stress is going to grow rapidly with the increased ratio of diameter of main cable section to the span (section-to-span ratio). When the section-to-span ratio exceeds 1:400, the secondary bending stress becomes greater than 30% of the primary stress. This shows that it is reasonable to ignore the secondary bending stress after completion of long-span suspension bridge, but the secondary bending stress of bridges under construction, especially that of a short-span suspension bridge, cannot be ignored. Compared to analysis using straight beam element, analysis using the independently developed curved beam element results in larger model and greater precision, and is more suitable for analysis of short-span suspension bridge model.As for main tower, mechanical properties of main tower under construction with the main cable not yet attached are analyzed by comparing with main tower after completion, where the effects of main cable and other members are considered after completion of the bridge. Elasticity and elastic-plastic analyses are done. The instability and failure modes of main tower of suspension bridge are examined in a qualitative way. Quantitative analysis is done to address the margin of safety for the main tower. Results suggest that for the computational models discussed here, although both the main tower under construction and the main tower after completion have the same type of instability issue, which is elastic instability, they have different boundary conditions. Hence, they have different modes of elastic instability and significantly different elastic-plastic ultimate bearing capacities. Analytical results of the main tower under construction are to overestimate the axial compression load capacity under real working condition after completion of the main tower.Seismic properties of suspension bridge at different stages from unloaded cable to completed bridge are examined by comparing again with the structure after completion.Because of the comparison with completed bridge, it is first necessary to study the seismic properties of the completed structure.Specific to different physical quantities, the paper examines various factors one by one, including geometrical non-linearity, direction of seismic ground motion input, and artificial ground motion recording power spectrum, to see how they affect the analysis results of response time history of bridge to earthquake under single-point excitation. Results indicate the following: (a) during the single-point excitation analysis, geometrical non-linearity does not have much effect; (b) there are significant differences between the results of multi-dimension and single-dimension analysis and the 3D seismic motion analysis should be used; and (c) Relative to other models, Kanai-Taijimi model generates seismic motion excitation that is more suitable for analysis of earthquake response time history of long-span suspension bridge. Based on these findings, multi-point elastic-plastic and incremental dynamic analysis of time history are done with the model of Jianyin Bridge. Results of the analysis suggest that the main tower will basically remain its normal working condition in rare cases of an earthquake at seismic fortification level 7. According to the results of numerical analysis, in the rare cases of an earthquake above level 9, the main tower may become at risk. This means that the Bridge has a considerable margin of safety.Seismic properties of Jiangyin Bridge under construction (with stiffened girders being hoisted) are examined while the construction is under way. Results of such analysis indicate the following: (a) natural vibration period of the structure under construction is longer than that of the completed bridge, and the vibration mode sequencing of the same order would change as the construction moves on; (b) time-history analysis finds that the response of structure under construction is smaller than that of completed structure when the excitation input is modest (<400 gal). Under such circumstances, as long as the design can guarantee the safety of completed structure, the structure during construction stage would be safe too. When the excitation input is greater, the geometrical non-linearity during construction would cause the main cable's stiffened girder system sway noticeably, and thus make the response of the structure under construction way greater than that of completed bridge. Some provisional connections are recommended during construction to restrain the swaying displacement of stiffened girders against risks.
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