A constitutive model considering creep damage of wood

The serviceability of wooden structures involves multiphysical phenomena, notably the interactions among creep, plasticity, and damage. The influence of creep on the initialization of the damage and on its growth and spread can be adjusted by an additional alpha parameter in order to take into account the coupled effect between creep and damage more properly. We integrate an orthotropic viscoelastic model, based on the generalized Kelvin chain, with an orthotropic damage model, capturing both the immediate nonlinear elastic-plastic-damage response and the time-dependent viscous response of timber. The combination of these material models is important to obtain a realistic description of wood behavior, because the timber shows an immediate nonlinear elastic-plastic-damage response, but also the time-dependent viscous response. In this paper, we algorithmize, implement, and validate the concept of 'creep damage', a phenomenon observed in wooden structures. Benchmark tests reveal two distinct patterns of damage in beech wood, immediate postload damage that evolves over time and damage that occurs and spreads during the loading period.OA-hybri

Dynamic analysis of viscous material models

summary:The article deals with the analysis of the dynamic behavior of a~concrete structural element during fast dynamic processes. The constitutive material model must be chosen appropriately so that it takes material viscosity into account when describing the behavior of material. In this analysis, it is necessary to use fairly complex viscous material models which can affect, for example, vibration damping and the dependence of strength or even of the entire stress-strain curve on the strain rate. These relatively complex models are often formed via the combination of viscoelastic models with viscoplastic models or viscous damage models. Numerical simulations are performed for these models. The numerical analysis is validated by experimental measurements

On the Nonlinear Transient Analysis of Structures

This chapter consists of four sub-chapters the first of them is the introduction. The second sub-chapter discusses the suitability of the explicit and implicit methods for seismic analysis of buildings exposed to a substantially nonlinear response. Taking into account a duration typical for earthquakes from several seconds to about twenty seconds, it seems that the implicit method is more suitable. Because of the shape of accelerograms, it is needed to use quite short time steps. Both methods were compared for a heavily nonlinear response, typical for seismicity. The third subchapter discusses the analysis of the time-dependent behavior of concrete using nonlinear time-dependent material models during fast dynamic actions. Huge plastic yielding or damage of the material is reached. The fourth sub-chapter discusses sources of dynamical damping that are needed in earthquake analysis. This subchapter aims to take into account the influence of different kinds of damping in the dynamic analysis of structures. More advanced analysis taking into account the various sources of damping, i.e., material viscosity, plasticity/damage, and friction in connections and supports is strongly recommended in the earthquake analysis

Srovnání numerických výpočtů statického zatížení nosníku

This bachelor thesis is focused on wooden beams with rectangular cross-section. During static assesment of beams is suitable to calculate the deformations of beam as accurately as possible but linear elastic material models underestimate it as long as load exceeds linear elastic limit from which the material behavior is nonlinear. It is better to use elasto-plastic material model to describe a real behavior of wood. The aim of the work is to analyze and compare linear and nonlinear behavior of wooden beam for different boundary conditions. This work deals with spruce beam, two kinds of loads and two kinds of supports. The numerical solution is based on finite element method in Ansys software using 1D as well as 3D elements. Numerical results were compared with analytical solution to validate the numerical model for all variants of beam with linear elastic material

Dynamic Damping - Comparison of different concepts from the point of view of their physical nature and effects on civil engineering structures

summary:Sources of dynamic damping may be various. Mostly, the damping is implemented into calculations in a form of introduction of damping forces, as a product of the velocity vector and the damping matrix in an equation of motion. In practice, the damping matrix is usually assumed to be a linear combination of the mass matrix and the stiffness matrix (so called Rayleigh’s damping). This kind of damping primarily assumes the external environment viscosity as the source of damping, even though the part of Rayleigh's damping with the stiffness matrix implies the internal damping of the material. Explicitly, the internal viscosity of the material is respected using the appropriate material models. The relation between the Rayleigh damping and the Kelvin-Voight viscosity is shown in the paper. Dynamic damping occurs even when using non-elastic materials, where the unloading takes place in a different path from the loading and thus it leads to dissipation during loading cycles. The paper deals with the comparison of different types of damping of the oscillation of a building structure. The main aim of the paper is to recommend to apply the viscous material model instead of the obsolete and physically unjustified Rayleigh damping in the nonlinear dynamic time analysis of structures