Design Requirements For Diaphragm In Welded Moment Connections Between Box-shape Columns And H-shape Beams In Steel Frame

In the field of research of steel structure, the researches for connections, strength and buckling play similar important roles respectively. As a general structural form, various researches for steel frame are popular in scholars, in which many researchers pay more attention to steel moment connections. Although box-shape column is widely used in practice, the design method of welded moment connections to box-shape column is not explicit in the specification. Thus the importance of research for the behavior of the connections has been widely noticed. In order to make up the absence in the specification, and to understand the behavior of the connections, and to primarily serve the structural design, extensive researches are presented in this paper.Moment connections were selected from external sub-frame. Finite element models for 4 kinds of connections were generated in this paper. Nonlinear parametric analysis was conducted for 71 models to understand the whole behavior of the connections. Three major parameters which affect capacity of connections were expanded. It shows that the capacity of connection is not dominated by just a certain parameter. The parameters are correlated and influenced each other. However, it is difficult to determine the capacity of the connection from the results of FEM, because the results are vague and complicated. Thus further theoretical analyses were conducted in this paper.Firstly, theoretical analysis for deformation of the connection was conducted in this paper. It shows that structural deformation is composed of the unitary deformation caused by structure and local deformation caused by bending of flange of column. Local deformation was analyzed with bending theory of thin plate and solved with energy method. Because of difficulties in selecting proper function of bending deformation for the flange of column, discrepancies between analytical results and FEM results are obvious. However, the respective trend of the deformations of them is similar. Thus the first design requirement for diaphragm in welded moment connections between box-shape columns and H-shape beams in steel frame is properly proposed.Further, theoretical analysis for capacity of the connection was conducted in this paper. Three mechanisms were introduced for 2 categories of connections: the width of beam is equal to and the width of beam is not equal to that of column. The formula of capacity of connections was educed respectively. The results of theoretical analysis and that of FEM are well corresponded with each other, and the results of theoretical analysis is generally less than that of FEM. Finally, contrasts between theoretical results and FEM results were conducted. It shows that theoretical result certainly represents the limit state of capacity of the connection. Thus another requirement is proposed based on the capacity limit state of the connection.The requirements based upon the stiffness and the capacity limit state of the connection for diaphragm in welded moment connections between box-shape columns and H-shape beams in steel frame are finally validated.