C-K4K4 HSS-to-HSS moment connections

Section K4 on HSS-to-HSS connections under moment loading is applicable to frames with partially restrained or fully restrained moment connections, such as Vierendeel girders. The provisions of Section K4 are not generally applicable to typical planar triangulated trusses, which are covered by Section K3, because the latter should be analyzed in a manner that results in no bending moments in the web members. Thus, K-connections with moment loading on the branches are not covered by this Specification.

Available testing for HSS-to-HSS moment connections is much less extensive than that for axially loaded T-, Y-, cross-, and K-connections. Hence, the governing limit states to be checked for axially loaded connections can be used as a basis for the possible limit states in moment-loaded connections. Thus, the design criteria for round HSS moment connections are based on the limit states of chord plastification and punching shear failure, with $\phi$ and $\Omega$ factors consistent with Section K3, while the design criteria for rectangular HSS moment connections can be based on the limit states of plastification of the chord connecting face, uneven load distribution, and chord sidewall local yielding, crippling, and buckling. The "chord distortional failure" mode is applicable only to rectangular HSS T-connections with an out-of-plane bending moment on the branch. Rhomboidal distortion of the branch can be prevented by the use of stiffeners or diaphragms to maintain the rectangular crosssectional shape of the chord. The limits of applicability of the equations in Section K4 are predominantly reproduced from Section K3. The equations in Section K4 have also been adopted in CIDECT Design Guide No. 9 (Kurobane et al., 2004). For additional information on chord sidewall failure due to in-plane and out-of-plane moments, reference CIDECT Design Guide No. 3, pp. 62 (Packer et al., 1992).