چكيده به لاتين
Optimal design of structures has been the subject of considerable research over the past few decades, resulting in cost-effective designs. The main part of the cost of a structure is contributed by quite a few factors, among which the amount of steel material used is of profound importance. The primary objective of designers, therefore, is to minimize the weight of the structures. The beam-to-column connections have a great effect on the weight of the frame and, considering an equivalent weight for the connections, on its total cost. Simple and fully restrained (FR) connections are often idealized as pinned or fixed, respectively, for the purposes of structural analysis. Once the analysis has been completed, the deformations or forces computed at the joints may be used to proportion the connection elements. In certain cases, the deformation of the connection elements affects the way the structure resists load and hence the connection must be included in the analysis of the structural system. These connections are referred to as partially restrained (PR) moment connections. For structures with PR connections, non-linear behavior of them, as shown in numerous studies, should be considered. The most important behavioral characteristic of the connection can be modeled by a moment-rotation curve. Examples of procedures to model connection behavior are given in this study. In this research, an attempt has been made to obtain an optimal design for the frames, utilizing the colliding bodies optimization algorithm (CBO), enhanced colliding bodies optimization algorithm (ECBO), and vibrating particle system (VPS), and also considering the nonlinear behavior of connections. In this regard, two numerical examples, a nine-story single bay and a ten-story four-bay frame, were investigated. In both cases, the overall cost of the structure was observed to be less than that of the structure with fully restrained connections. Furthermore, all of the three algorithms showed an acceptable performance.
The secondary objective of this study was to evaluate the influence of partially restrained connections on the weight of the structures and their overall cost. In this regard, a series of 4-bay frames with different number of stories but under the same loading conditions were considered. Based on the results, in the case of shorter frames, utilizing the partially restrained connections led to a more uniform distribution of moment, and hence reduction of the maximum moment for most of the elements, reducing the weight of the frames. Moreover, considering the connections as partially restrained resulted in a noticeable reduction in overall cost of the structures. On the other hand, for frames with greater number of stories, the algorithm mostly considered the connections as fully restrained. This matter was due to the increase in displacement of the structures, reducing the difference between the cost of the structures with fully restrained and partially restrained connections. From the results, therefore, it may conclude that for multi-story structures it is preferred to use fully restrained connections instead of partially restrained ones.
