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۱OPTIMUM PLACEMENT AND PROPERTIES OF TUNED MASS DAMPERS USING HYBRID GENETIC ALGORITHMS
نویسنده(ها): ،
اطلاعات انتشار: International Journal of Optimization in Civil Engineering، اول،شماره۱، ۲۰۱۱، سال
تعداد صفحات: ۲۱
Tuned mass dampers (TMDs) systems are one of the vibration controlled devices used to reduce the response of buildings subject to lateral loadings such as wind and earthquake loadings. Although TMDs system has received much attention from researchers due to their simplicity, the optimization of properties and placement of TMDs is a challenging task. Most research studies consider optimization of TMDs properties. However, the placement of TMDs in a building is also important. This paper considers optimum placement as well as properties of TMDs. Genetic algorithms (GAs) is used to optimize the location and properties of TMDs. Because the location of TMDs at a particular floor of a building is a discrete number, it is represented by binary coded genetic algorithm (BCGA), whereas the properties of TMDS are best suited to be represented by using real coded genetic algorithm (RCGA). The combination of these optimization tools represents a hybrid coded genetic algorithm (HCGA) that optimizes discrete and real values of design variables in one arrangement. It is shown that the optimization tool presented in this paper is stable and has the ability to explore an unknown domain of interest of the design variables, especially in the case of real coding parts. The simulation of the optimized TMDs subject to earthquake ground accelerations shows that the present approaches are comparable and\or outperform the available methods.

۲Behaviour of wrapped hsc columns under eccentric loads
نویسنده(ها):
اطلاعات انتشار: Asian journal of civil engineering، چهارم،شماره۲-۴،October۲۰۰۳، سال
تعداد صفحات: ۱۰
With the technology development on the compressive strength of concrete over the years, the use of high strength concrete has proved most popular in terms of economy, superior strength, stiffness and durability due to many advantages it could offer. However, strength and ductility are inversely proportional. High strength concrete is a brittle material causing failure to be quite sudden and ‘explosive’ under loads. It is also known that true axial compression of structural concrete columns (axially compressed) rarely occurs in practice. The stress concentrations caused by the eccentric loading further reduce the strength and ductility of high strength concrete. This paper presents results of testing eccentrically loaded columns externally wrapped with different types of materials. The experimental results show that external reinforcement can enhance the properties of high strength concrete columns.

۳Moment Coefficients for Statically Indeterminate Prestressed Concrete Structures
نویسنده(ها): ،
اطلاعات انتشار: Asian journal of civil engineering، دوازدهم،شماره۱، Feb ۲۰۱۱ ، سال
تعداد صفحات: ۲۲
In statically indeterminate prestressed concrete structures, prestressing force producessecondary moment in addition to primary moment due to eccentricity. This condition isdifferent from statically determinate structures where there is no secondary moment effect and the moment due to prestressing is due to primary moment only, i.e., prestressing force times eccentricity. With the presence of secondary moment, prestressing force design becomes more complex, because the secondary moment is a function of prestressing force and the geometry of the structures. In addition, considering that in general the cable profile is parabolic or another type of curves, which also occurs at continuous supports, the load balancing method may not be used. To cope with this problem moment due to prestressing force is assumed to be the prestressing force times a β coefficient. In statically determinate structures the β coefficient equals the cable eccentricity to the center of gravity of the section. Therefore, the β coefficient can be considered as a statically indeterminate eccentricity. By assigning that the moment due to prestressing force as a function of prestressing force and by considering the allowable stress requirements at top and bottom fibers, equations can be derived to compute the prestressing force in statically indeterminate structures. From the derived equations, the upper and lower bounds of prestressing force can be determined if the section satisfy the requirements. If the optimum prestressing force is needed, the difference of lower and upper bounds should be minimum. Nevertheless, the difference of lower and upper bounds can be considered as a safety level. At the end of thepaper examples are presented to show the application of the proposed method.
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