Development of damage models for masonry construction elements and applications of finite element

During the project and construction process strength of the materials being used should both be known as individual parts and as construction elements. With this aim, for example some standard cube or cylinder test specimens are taken from the concrete during casting. The steel specimens are taken from the reinforced concrete being used for reinforcement. Tensile tests are carried out. The concrete compressive strength at 7 or 28 days can be compared with target rates or the rates used in project calculation. Wall elements which can be used as filling material in a reinforced concrete or in steel frame or as only masonry construction elements individually are very important construction elements. The evaluation study of these infilling walls with the frames is considered of increasing importance. In the event of their use as masonry, or as a built up construction element, the carrying capacity of the walls becomes important. In such a case, the method to determine the compression strength of a masonry wall is to test prisms made of the masonry unit, mortar and grout used in the wall. The size of these prisms must be selected for reflecting the behaviour of the wall under the axial load or the failure mechanisms. For this purpose, in these studies, standards and codes of the fact that this size, the height to thickness ratio, is selected as between 2 to 5; the same dimensions will be used with tests for the general failure mechanisms of the masonry wall. Hence, rather than testing the large sized masonry walls, a common standard implying the use of these masonry prisms has been developed. In the event of the use of the masonry wall as filling material of reinforced concrete or steel frames, in these studies the masonry prisms, made of the same material of the masonry wall, are tested. It can be considered that these masonry prisms are identical to the cube or cylinder specimen taken from the concrete. Or this can be named as the specimens taken from masonry wall or filling wall. The use of these masonry prisms to determine the strength of historical masonry buildings is also possible. With this purpose, two or three masonry units taken from the historical building can be tested in the same way as a masonry prism. In the studies carried out until recently, the hollow or grouted masonry prisms have been tested under axial strength to examine the behaviour of the concrete masonry prisms. Some of researchers leaning on their own conducted test results proposed some relations to estimate the compressive strength of the concrete masonry prisms. On the other hand, in order to examine stress-strain relationships of the stack bond prisms, some researchers have conducted researches with linear finite element analysis. In this study, nonlinear three-dimensional finite element models of effective block, mortar and grout materials of hollow block and grouted block prisms that compare with the existing test results in the literature have been conducted using LUSAS program. The prisms that their models have been finite element of three-course block masonry prisms by using LUSAS, both the elasto-plastic (Drucker-Prager failure criteria) and isotropic damage models (Oliver model) are activated to reflect the analysis of nonlinear behaviour of blocks, grout and mortar. According to the findings of conducted research, in relation to block strength, mortar and grout concrete strength, concerning Drucker-Prager failure material parameters cohesion and internal friction angle and material damage values, plenty of correlations have been suggested. By using the results of these analyses, a simple analytical relation is proposed to predict the compressive strength of hollow and grouted prisms. The most important attribute of these relations is that they have been acquired through nonlinear analyses. In this respect, the behaviour of the prisms could be estimated more realistically. By utilizing recommended material parameters, the model of prisms can be analyzed by means of finite element packet programs. Consequently, hollow prisms and grouted prisms that are filled by various concrete compressive strengths have been tested in YTU laboratories. The way of behaviour has been observed by testing these prisms. Furthermore, three dimensional nonlinear finite element analyses of tested prisms have also been conducted. Through these analyses, the test and the proposed relations results have been compared and the results have been observed to be in good agreement. Keywords: Compressive strength; Masonry prism; Hollow block; Three-dimensional model; Finite element method; Drucker-Prager yield criterion; Isotropic damage; Grout; Stack bond.