عنوان مقاله [English]
The steel moment resisting frames are used as a one of the ductile systems for bearing earthquake lateral forces. The behavior of rigid beam-column connections has the major effect on the steel moment resisting frames.in order to provide required rotational capacity and ductility of connections. The typical connection which is offered in design codes such as Iranian code 10th was used. In some of the common executions in Iran, a special method knows tree-column is used in which the increasing of the beam section from plastic area to column’s face in provided by tapered sections. This kind of connection is not a typical so its behavior hasn’t been already considered. Based on a parametric study, using finite element analysis, the dimensions of effective geometrical variables for the tapered beam web like the length and height was studied. In addition, one specimen was tested to clarify their cyclic behavior. The results showed a satisfactory performance for these kinds of connections by using vertical stiffeners within the tapered zone of the beam so that their height is about 0.8 to 1.2 of section height. Also, the requirements of the code are met to confirm this kind of connection. Then, reforming the models of finite element, if required, more parametric studies to identify the behavior of connections will be done, as identifying of drawbacks. So the possible solutions for improving their performance will be considered. Due to increase of section’s height along the length of tapered section, the instabilities of web are possible. Studying the possibility of web instabilities and local buckling’s, the capacity and ductility of this kind of connection, assuming the possible failure mechanisms, is considered using the plastic analysis and the theory of yield lines. Also, as considering the common method in analysis and design of structures contained tree- column and tapered sections, the accuracy of these method will be assessed and the ways of enhancing the accuracy of common method of design will be studied.