Project Title Weld Design for Rectangular HSS: T-/Cross-Connections Under Branch Bending and Overlapped K-Connections
Principal Investigator Jeff Packer
Research Institution University of Toronto
Project Period 2011 - 2014

Overview and Objectives: AISC has now introduced a new section (K4) on “Welds of Plates and Branches to Rectangular HSS” in the 2010 Specification which – besides containing weld effective length rules for axially-loaded T-, Y-, Cross- and gapped K-connections – has expanded the scope to also cover weld effective length rules for branch bending in T-, Y- and Cross-connections, plus weld effective length rules for overlapped K-connections under branch axial load. These additional weld design recommendations are speculative, as there is no supporting research justification, but based on the judgment of the HSS TC. There is thus a need to evaluate the validity of, and potentially modify or simplify, these new aspects of Section K4 in the Specification.

Work Description:

Phase 1 - Experimental study of weld effective lengths in rectangular HSS T-connections subject to branch in-plane bending.
A series of square HSS-to-HSS 90º welded T-connections will be designed, such that they are weld-critical (rather than failing by known connection failure modes), under application of branch in-plane bending moment. These connections will be carefully fabricated with a common weld effective throat around the branch member, subjected to weld inspection and geometric measurements, then loaded to weld failure in a quasi-static manner.

Phase 2 - Experimental study of weld effective lengths in rectangular HSS overlapped K-connections under predominantly branch axial loading.
Using the experience of similar tests on gapped K-connections, one large-scale 40-foot span, simply-supported, rectangular HSS Warren trusses, comprised of welded overlapped connections, will be designed and fabricated. The weld-critical connections will vary the amount of overlap (25% ≤ Ov ≤ 100%), the branch-to-chord width ratio (β) and the chord wall slenderness (B/t), within the Limits of Applicability of Section K2.3 of the Specification (AISC, 2010). By means of quasi-static point loads to chord panel points, in a carefully planned manner, sequential failure of the tension-loaded welded joints can be obtained. Such experimentation has been performed successfully before and the same universal machine and laboratory space is available.

Deliverables: Deliverables include research reports, journal papers, and appropriate guidance to Specification provision revisions, if needed.

Benefit: Experimental validation of effective length provisions for branch bending in Chapter K of the Specification.