عنوان مقاله [English]
Masonry buildings are some of the most popular structures in Iran. Unfortunately this type of building is very vulnerable during earthquakes. Masonry walls are the basic elements providing strength and stiffness to
masonry structures. Experimental results of masonry prisms show significant variations in the strength and stiffness of the units. The purpose of this paper is to study the effects of variations in the properties of masonry units in the behavior of masonry walls. In view of the lack of material data, Monte Carlo simulations are used in the analysis of walls. Statistical data collected on real materials are used in the analysis. These include compression strength, tensile strength and modulus of elasticity. These basic parameters are modeled as random variables. A finite element model of the wall is used, along with the said random variables. The validity of the finite element model is established by three different checks: Comparison with closed form solutions, experimental
results and code formulas. From the Monte Carlo simulation, two parameters were obtained; ultimate displacement and maximum strength. These were extracted from a pushover, nonlinear analysis .
A parametric study was conducted in order to establish the effect of various parameters on the behavior of walls. The parameters included wall thickness (with two values 22 and 35cm), gravity load, based on the tributary area of the roof (roofs with 2 or 4 m spans), quality of material (fair, good), and type of lateral load simulating earthquake (with uniform, stepped and triangle accelerations, as well as displacement of a point of the roof). The last parameter was in the presence or absence of tie beams. The results show that gravity load will affect the maximum strength of the wall, as well as the final displacement. The type of lateral load will affect maximum strength, final displacement and their distribution probabilities. This is a noteworthy result, because the pattern of lateral load is a significant factor in pushover analysis. In masonry walls without tie beams, the strength of the wall increases with the use of good material. However, for the same type of wall, the final displacement is reduced with the use of good material. This is despite the fact that the use of good material increases both strength and final displacement in walls with tie beams. In other words, in the latter, wall ductility is increased. Another conclusion is that the coefficient of variation of the final displacement is larger than that of the maximum strength. This discrepancy can be up to 20 times. Therefore, when designing a masonry wall, it is much more difficult to reach a target displacement than a specific value of strength.