Caculation Theories And Tests Research On The Ultimate Capacity Of The Long-Span Steel Bridges

Some indicators of the China's long-span steel bridge constructions had been catching up with the international advanced levels, but lagged behind in basic theoretical researches, which lagged behind engineering practice more seriously. Along with the development of China's bridge constructions, the longer span of steel bridges, the taller height of bridge towers, the thinner plates of box girder, the extensive application of high-strength steels, as well as the development of whole welded in steel bridge fabrications, so that the local and overall structural stiffness declined, which made bridge stability is more important than ever. There is an urgent need for model tests and theoretical study in depth for steel bridges on the key technology, ie. stability and ultimate strength. Crashed of the four large steel box girder bridges during construction in the 1970s in Europe was the new starting point of the bridge stability research. It is also shown that the limit capacity theory should be guidelines to the bridge designings. Analyzed the ultimate strength of steel bridge structure, not only can be used to limit state design, but can understand its destructive forms, accurately know its overloading capacity and safety reserve with the given loads, provide the gist and guarantee for the security construction and operation.In this thesis, based on summarizing and learing from the achievements in the pioneer's works on the bridge stability, the limit capacity of plate and steel plated structures. With theoretical and numerical analysis, the limit capacity of plate and steel plated structures had been investigated comprehensively and systematically. The study of this paper as follows:1. Summarized and commented the stability theories of steel bridges and the ultimate strength theories of steel plated structures. On the basis of its basic theories, research ideas, analysis methods and current level etc., systematically summarized its study history and current status, commented its achievements, and pointed out the questions on the ultimate capacity of plates and steel plated structures currently, which can give references to research on the ultimate capacity of long-span steel bridges. 2. Research on the ultimate capacity of steel plated structures. To analyze the ultimate capacity of steel plated structures finally can be idealized as investigated the ultimate capacity of a rectangular plate with arbitrary elastic boundaries loaded in plane. In this paper, considered residual stress as equivalent residual stress loads, researched on the large deflection equations of plates with initial imperfections, applied the thickness discounted quantity of plate as perturbation parameter, assimilated between the applied plate with initial imperfections and the perfect plate, acquired the thickness discounted quantity of perfect plates and the thickness discounted equations of steel plated structures. Validated by the results of nonlinear FEA and experiments, the thickness discounted method (TDM) is practical with good precision. According to nonlinear FEA, had comprehensive investigated the effect by initial imperfections of steel plated structures.3. Comprehensive summarized the research history and the possible reasons for the plastic paradox. Though numerical methods, contrasted the effect of plastic buckling by the flow theory and the deformation theory of plasticity, and the other reasons which may causes plastic paradox. According to detail analysis of the pastic buckling experiments and theoretic research, deemed that plastic paradox is not exist in numerical analysis, which was mainly caused by the approximate supposition in theoretic researches.4. Researched on the unified ultimate capacity theory(UUCT) for steel plated structures. Promoted the effective width theory to analysis the steel plated structures, gained the unification formula for the post-buckling ultimate strength of steel plated structures and the gradual destruction method to analysis the ultimate strength of complex steel plated structures, and validated the UUCT by nonlinear FEA. Through analyzed the ultimate capacity of simple-supported board plate with pressure loading, validated the application range of the UUCT. Research on the effect of torsion stiffness by elastic boundary, extended the results of simply supported plates to plates with elastic boundaries. Research on limit capacity of the simple-supported plate, loaded uniform shear load, non-uniform load and combination loads, systematically researched on how to apply the UUCT, and validated the reasonable of the UUCT by nonlinear FEA. Therefore, TDM, the unification formula and randomicity research on the limit capacity of steel plated structures be called by a joint name——the unified ultimate capacity theory. 5. Researched on the application of the UUCT for the steel plated structures. By the unified theory, researched on the limit capacity of I-section steel girders with shear loading, patch loading and combined loading, research on the stiffened plates with pressure loading. Through comparing research between tests result and nonlinear EFA, the new methods are reasonable than the known theoretical formulas.6. Reviewed the development of highway steel bridge design theories in China, through contrasted between domestic norms and overseas norms for the steel bridge designing, based on the reliability theories, brought forward the suggest value of reliable indicators and the ultimate capacity design methods for the steel plated structures. Stochastic nonlinear finite element method has been developed base on Ansys software. With it, researched on the effect by the stochastic design parameters of steel plated structures, received the sub-factor for the ultimate strength design.7. Researched on the ultimate strength of steel columns by the ultimate capacity theory. Systemically discussed the effect for strut's bearing capacity by initial imperfection, rebuilt the new checking formula by amended Shanly model. By analytic method, research on the dominate equations of simple supported columns with eccentric loading, gained the direct reasons of that results of double-module theory is large than tests. Probability analyzed on the ultimate strength of steel struts, acquired the sub-factor for the ultimate strength design.8. Based on the flat steel box girder segment experiments of Huangpu Bridge, over Zhujiang river, studied the construction stability of the long-span cable-stayed bridges during suspender installation, and the mechanical properties of truss diaphragms. Through contrasted between the test and the finite element method, verified the unified ultimate capacity theory of steel plated structures proposed in this paper.