Dynamic load capacity of the steel lattice girder under cycle impulse load

摘要

The paper presents a solution of the analysis concerning the behavior of the steel lattice girder under a cycle of dynamic impulse I=P·τ_0. In this analysis I use the theory of shakedown. I assume that this load causes anon elastic reaction which it contain dissipation of energy, so we have to continue the deformations and residue forces in the rods. At a certain intensity of these forces, the construction can reaction subsequent cycles of load without further dissipation of energy, i.e. in the field of secondary elastic. This condition is referred to as adapting the structure to the objective of cyclic loading. Lattice girder models the system of the masses gathered combined hinge of tension members and discrete compression members. Obtaining solutions requires a theory of moderately rods. Solution system dynamics are looking for using of the finite difference method with explicit time integration scheme. I look for shakedown load capacity by direct analysis of the dynamics of the girder in the area non elastic, by checking if there is a loss dissipation of energy in next cycles of loading. Thus determines the member of possible repetitions of the assumed impulse load exceeding which generates no longer increases dissipation of energy. In the analysis I take into account the possibility buckling compression members and consequently the non-elastic vibration in the longitudinal and transversal geometric nonlinearity range. The main issue is to determine after the next cycle of the load state of inelastic displacement nodes and residual internal in the rods. These amounts represent the initial condition to describe the load cycle. It is possible to use the approach presented in the paper, in order to assess the relevance of the type of accidental action. In such cases, it is assumed that low times of the impact of accidental action and assumed irreversible serviceability limit states with criterion limit deformation permanent structures or amplitude displacements and deformations. The intensity of the accidental action is greater than the shakedown load capacity. I use model of deformation of the material: perfectly elastic-plastic. The theory of shakedown is illustrated by the described examples.