Nonlinear Analysis Of Static And Dynamic Properties Of Long Span Cable-stayed Space Truss

Long span cable-stayed space truss consists of three basic parts, such as stayed cables, space truss and tower. Compared with cable-stayed latticed structure, it has many advantages not only in fewer members, joints as well as convenient construction, but also in aesthetic appearance. Therefore, it is a kind of hybrid structural system with good developing prospect.In this dissertation, according to the fundamental principle of continuum mechanics, nonlinear finite element theory is introduced. The difference between Total Lagrange formulation and Updated Lagrange formulation is discussed. Based on the equation of updated Lagrange formulation, nonlinear stiffness matrixes of elements are deduced, which contain a 3-dimension bar element for large displacement and infinitesimal rotation analysis ,a cable element and a 3-d beam element. Subsequently, nonlinear mixed finite element equation of the whole structure is formed.The paper discusses the types of structural configuration, including the cross sections of space truss, cable layout, and the form of tower. Two towers with three spans and one tower with two spans are commonly used in structural system of long span cable-stayed space truss. For these two structural systems, the analytical models are studied, and some special features about internal forces and deflection under vertical load can be obtained. The influence of several important parameters in the process of design is investigated, such as heights of tower and truss depths, distances between inclined cables as well as stiffness of tower and cables. Some conclusions are drawn as reference for primary design.The primary sources of geometric nonlinearity of the structural system are investigated. The cable sag, large displacement of the system as well as both of them taken into consideration are discussed respectively for two structural systems in this analysis. The results are shown that geometric nonlinearity has fewer effects on cable forces, but relatively great on the axial forces of truss and bending moments of tower. By use of two kinds of planar and spatial models, geometric nonlinearity, material nonlinearity and dual nonlinearities are considered to analyze of the load-carrying capacity fort two kinds of structural system. It is shown that the ultimate load-carrying capacity only considered geometric nonlinearity can be overestimated. The geometry nonlinear influence is not very obvious; therefore, structure actual limit bearing capacity can be controlled mainly by the material nonlinearity. Moreover, some other factors affecting ultimate bearing capacity are studied in order to have a further understanding of stability properties, such as heights of tower column, truss depths, distance between inclined cables, stiffness of cables, and pretension. It can be found from results that the influence of the distance between inclined cables is the greatest. As it reduces, limit bearing capacity increase obviously.The determination of pretension and the influence of pretension on the performance of structure are also researched. Because of many kinds of factors, cable corrosion in cable-stayed structures is unavoidable. Therefore, part or all stayed cables have to face the problem of being replaced after a few years. Based on this, iteration method is proposed for the first time to solve the problem that both the stiffness of the whole structure and equivalent concentrated node loads are changed after removal of cable with initial pretension. The formulation is derived and the convergence speed is also discussed. An iterative procedure is used to analyze the new structure with variation. By means of this method, repeated analysis is avoided when calculating the new structure because the whole iterative process is performed within the range of change in stiffness of original structure involving nodal degree of freedom. Therefore, the volume of calculation is greatly decreased. The method is suitable for not only the removal of any cable but also that of a few cables at the same time.Through the analysis of characteristic of natural vibration, it can be seen that the natural period of vibration of this structural system is much longer and frequency spectrum is denser. The CQC mode combination method should be adopted to calculate the structure response and 20 modes are suitable to participate in the combination when response spectrum method is made use of. The influences of some parameters on characteristic of natural vibration are also researched. By use of response spectrum method and time history method, the seismic responses of structures under horizontal earthquake are studied. At the same time, under strong earthquake, the elasto-plastic dynamic action is investigated under dead loads and horizontal seismic loadings. The comparison is made between a linear and nonlinear earthquake-response analysis by the step-step integration procedure. Through analysis, the weak positions can be found, which provide the basis for structural design.The analyses of both time history and vertical response spectrum are performed under the action of representative 1 vertical seismic wave. The calculated results of two methods are basically consistent. The magnitude and distribution of vertical seismic internal force coefficient are studied under vertical earthquake and the table for vertical seismic internal force coefficient has been summarized. It can be found that vertical seismic internal force coefficient is related to structural form and span besides site and earthquake intensity, which plays an instructional role for the earthquake resistance design of this kind of new structural system.At last, research work is summarized and the problems to be further solved are pointed out. The paper lays good foundation for further research to this structure, and gives beneficial references for practical application of the long span cable-stayed space truss.