Wyniki wyszukiwania - BazTech

1

Linear and Non-linear Creep models for a multi-layered concrete composite

Balevicius R., Marciukaitis G.

Archives of Civil and Mechanical Engineering

|

2013

|

Vol. 13, no. 4

472--490

EN

One- and two-dimensional linear and nonlinear creep models for predicting the time-dependent behavior of a concrete composite under compression are proposed. These models use the analytical and iterative solutions of the Volterra integral equation. The analytical approach is based on the age-adjusted effective modulus method, and the nonlinear technique applies an iterative approach to the system of non-linear equations, implying a generalization of the principle of superposition. Both models are validated in this study. It has been recently found that negative values of the aging coefficient can emerge in early age multi-layered composites when the stress redistribution between the layers is governed by the combination of considerably different creep strains and aging of the layers. In the plane-strain state, the two-dimensional creep analysis of multi-layered composites yields the same vertical stress-time history as that in a one-dimensional case if the Poisson ratios of the layers are equal. This is valid even though the average value of the vertical stress used to calculate the Volterra integral term is dependent on the Poisson ratio of the layers. In particular, the evolution of vertical stress with time is dependent only on the vertical strain and compatibility conditions in a direction parallel to the lamination. A fracture mechanics approach is also introduced to predict the gradual degradation of long-term strength for a multi-layered composite under a sustained compressive load. The results show that the stress redistribution near the crack-tip under the final period of a high level of sustained loading may lead to an additional required compressive stress for complete failure of the composite. Long-term failure primarily begins with the less deformable (stiffer) layers because the more-deformable layers can relieve the initial stresses. Thus, the long-term strength of the composite can exceed its instantaneous strength for early age composites or for composites composed of layers that possess considerably different creep and aging properties.

2

Microscopic and macroscopic analysis of granular material behaviour in 3D flat-bottomed hopper by the discrete element method

Balevicius R., Kacianauskas R. R., Mróz Z., Sielamowicz I.

Archives of Mechanics

|

2007

|

Vol. 59, nr 3

231-257

EN

The paper presents the application of the discrete element method to modelling of granular material filling and discharge in 3D flat-bottomed hopper. A mathematical model, as well as the developed software code, operates with spherical visco-elastic non-cohesive frictional particles. The evolution of granular flow, internal forces and densification (rarefaction) are characterized by macroscopic parameters such as the discharge rates, the porosity fields and the wall pressures, as well as by microscopic evaluations in terms of coordination number, velocity patterns and inter-particle contact forces. It was shown that qualitative characterization of flow may be done even by relatively rough models with small number of particles, which required to be increased, however, for more precise description of the localized phenomena. Unsatisfactory evaluation of the stress peak during discharge is presented as an illustrative example. The main focus of the paper is the analysis of particle friction effect and the consistency of micro and macro-phenomena in the time-dependent flow process.

3

Non-linear physical relations for reinforced concrete elements under long-term loading

Balevicius R., Simbirkin V.

International Journal of Applied Mechanics and Engineering

|

2005

|

Vol. 10, no 1

5-20

EN

The paper presents a method for modelling material non-linearity for use in the analysis of load-carrying capacity and deformations of reinforced concrete beams, columns and membrane-bending plates subjected to long-term loads. Physical relationships expressing relations between internal forces and stresses, strains and stiffness are derived on the basis of the fracture and creep theories for concrete and using non-linear stress-strain diagrams modified for time effects. A specific implementation technique of a genetic algorithm is developed to find multiple solutions to non-smooth problems under consideration. The computation technique proposed is found to be effective in numerical examples, and an adequate accuracy of the analysis is verified by comparison with experimental data.