STRUCTURAL PROPERTIES OF PANEL AND JOINT IN NON-DIAPHRAGM CHS TO H-BEAM CONNECTION

Abstract

 The non-diaphragm method for joining CHS-column and H-beam simplifies the connection details and facilitates the welding procedures of steel moment frames, while it requires a design method for semi-rigid connection as schemed in Fig. 1. In this study, structural properties of their panel and joint were experimentally investigated.
 Two types of specimen were tested: one is an X-shaped frame whose panel is subjected to shear, and the other is a 3-point bending specimen whose panel is free from shear. The experimental setup and the arrangement of displacement meters are illustrated in Fig. 3 to Fig. 6, and the specimens are listed in Table 1. The steel materials are summarized in Table 2 with their stress-strain curves in Fig. 2.
 The relationships of applied load and overall deformation are shown in Fig. 7 and Fig. 8, and the post-test pictures are shown in Fig. 9 and Fig. 10. It is observed that they are fairly ductile and tough accompanied by ample plastic deformation. The ultimate state of X-frame is governed by joint failure for the non-diaphragm style, while by panel failure partly associated with lateral buckling of beam for the diaphragm style.
 The curves of moment vs. shear angle of the panel in X-frame of the diaphragm type are shown in Fig. 11, from which measured strength and stiffness of the panel are given in Table 3. The method of determining the shear angle of the panel is illustrated in Fig. 12(1). The obtained effective volume of the panel in terms of strength as well as stiffness is found in accordance with the AIJ guideline.
 The curves of moment vs. rotation of the joint in X-frame and 3-point bending specimens of non-diaphragm style are shown in Fig. 13, in that the method of determining the joint rotation are shown in Fig. 12(2). Their joint properties are summarized in Table 4, and compared in Fig. 14. The ratios of strength are around 1.0, which indicates that the joint strength is not influenced by the panel shear. However, the ratio of stiffness is much larger than 1.0, which is attributed to the different actions of beam end moments.
 The strength and stiffness of the joint of the non-diaphragm connection calculated from the formulae proposed by the authors are put in Table 5, and compared with the experimental results. It is found that the predictabilities are satisfactory both for X-frame and 3-ponit bending, which indicates that the formulae are valid irrespective of the existence of shear in the panel.
 The load-carrying capacities of X-frame are shown in Table 6. The max ratio of non-diaphragm to diaphragm is 1.0. This suggests that the shear strength of the panel in non-diaphragm connection is not less than that of the panel in diaphragm connection.
 The shearing stiffness of the panel in non-diaphragm connection in X-frame is compared with that specified in AIJ guideline for diaphragm connection in Table 7. The ratio is close to 1.0, which suggests that the shearing stiffness of the panel in non-diaphragm connection is almost the same as that of diaphragm connection.
 On the assumption that the panel and joint behave independent without any interaction as shown in Fig. 15, the procedure of frame analysis for the cruciform sub-frame of Fig. 16 are extended to the X-frame. The analytical load-deformation curves are well coincident to those of the experiment as shown in Fig. 17.
 Conclusively, the structural behaviors of panel and joint in non-diaphragm CHS to H-beam connection are independent, and then the structural properties of the joint and panel can be calculated by the formulae previously proposed by the authors and the formulae specified in AIJ guideline, respectively.