Dynamic Characteristics Of Nonlinear Viscoelastic Structures And Seismic Control Of Long Span Space Shells

Long span space structures are widely used in important public buildings. They are complex not only on architectural modeling and construction technology but also on inner facilities of electricity, thermal and water supply. The geometrically nonlinear problems of long span space structures are very conspicuous because of their large span, thin thickness and light weight. In addition, long span space structures are often made by steel or aluminum alloy materials, the viscosity of materials will be greatly enhanced in high temperature environment or under an explosion, impact load or after being taken some vibration control measures. The structures essentially become a kind of viscoelastic or visco-elastic plastic structures on condition of mentioned above. The main motivation of this dissertation is to study the dynamic behaviors of several kinds of viscoelastic structures and the seismic control of long span space shell.Firstly, fractional derivative viscoelastic and visco-elastic plastic constructive model of steel and aluminum alloy material are proposed, which provided with strongpoint to describe the time and frequency effects. Subsequently in chapter 2, the creep experiment of aluminum alloy material and dynamic characteristic experiments of three polymeric materials are made to prove the advantage of fractional constructive model. Then, numerical computation schemes for fractional derivative are deducted in chapter 3. The results of silmulation sample shows that the proposed method possesses the advantages of fast convergence, higher accuracy and better stability.In chapter 4, the dynamic characteristics of autonomy and non-autonomy fractional Van Der Pol-Duffing system are discussed based on the numerical scheme proposed in chapter 3 and Runge-Kutta method. The results show that the responses of this fractional system are similar to classical Van Der Pol-Duffing system. Moreover, the order of fractional derivative can change the oscillation period and nonlinearity of the system greatly. In additional, the output energy under seismic loads can be varied by changing the fractional order, which can be used to seismic control.In chapter 5, the first and second order Galerkin methods are used to simplify the flat hinged shallow arch structure. The dynamic responses with varyiance of damping coefficient, fractional order and excitation amplitude are illustrated. The results show that this nonlinear system has complex dynamics phenomena such as period doubling bifurcation and chaos. In additional, there is coexistence of solutions found in the first order Galerkin system.In chapter 6, comparison is made to exposure the balance route of a two-bar plane truss structure under vertical loads, horizontal loads or compound loads. The research results show that balance route of the compound loads is more complex than the others, which is equivalent to vertical loads with horizontal disturbance, and the support capacity decreases under compound loads. Then, based on the phase portrait definition, the relationship of ultimate bearing capacity of structure with bifurcation and chaos is built. In this theory, bifurcation means critical condition and chaos means ultimate bearing capacity.The final part of this dissertation is engineering application. In chapter 7, the difference of dynamic characteristics between an elastic single-layer spherical shell with a viscoelasticity aluminum alloy single-layer spherical shell on condition of same span, same rise-span ratio and same member sections. The results show that the time-dependence of the material may affect the structure's dynamic behaviors greatly. In chapter 8, viscoelastic dampers are introduced into a single-layer spherical shell for seismic control and the dynamic performances of controlled shell and uncontrolled shell are contrasted. Parameter analyses are performed to investigate the influence of dampers'positions and parameters on seismic control effort. The results show that it is feasible to seismic control by viscoelastic dampers, but the control effort is greatly influenced by the dampers'location and parameters.