Περίληψη | The masonry of old structures varies in a wide range: geometry of walls and columns, type and
dressing of stones, joint constructions and materials, and others. Also repair work and strengthening techniques
of old masonry have a major influence on the mechanical behavior so additionally material models are needed
to describe the seismic behavior of strengthened masonry.
The masonry material constituting the structures of monumental and old constructions is often characterized
by very low tensile strength with respect to the compression strength. In parallel, masonry compression
behaviour is of crucial importance for design and safety assessment purposes, since masonry structures are
primarily stressed in compression. However, the compression failure mechanism of quasi-brittle materials is
rather complex, especially when compared with tensile failure.
The finite element method is usually adopted to achieve sophisticated simulations of the structural
behaviour. A mathematical description of the material behaviour, which yields the relation between the stress
and strain tensor in a material point of the body, is necessary for this purpose. This constitutive model must be
capable of predicting the behaviour of the structure from the linear elastic stage, through cracking and
degradation until total loss of strength.
Masonry is a composite material made of bricks and mortar, which exhibits distinct directional properties
due to the mortar joints which act as planes of weakness. In our research, on the numerical representation the
macromodeling of masonry as a composite is used, which is applicable when the structure is composed of solid
walls with sufficiently large dimensions so that the stresses across or along a macro-length will be essentially
uniform and also is more practice oriented.
Nonlinear behaviour of both components should be considered to obtain a realistic model able to describe
cracking, slip, and crushing of the material. Its yield behaviour is a strong function of hydrostatic pressure and
tensile yield stress and compressive yield stress, under uniaxial loading are different. In order to obtain a better
representation, individual yield criteria must be considered, according to different failure mechanisms, one in
tension and the other in compression. Something which is not so easy in many yield and failure criteria which
are already programmed to finite elements programs.
In this paper, some results of a parametric investigation about the applicability of widely used criteria like
the Drucker and Prager, the Parabolic Mohr- Coulomb and the Buyukozturk, in the dynamic analysis of
masonry wall are presented. The analysis was done, considering various dynamic loads in order to study the
influence of the selected criterion on the dynamic behaviour locally or globally of the structure. The correlation
of the results is concentrated on the effectiveness of the examined criteria to represent the real mechanical
behavior and the estimation of critical areas. Also the differences which are presented seems to be remarkable
when complicated dynamic loads are applied. | en |