Slotted end connections to hollow sections

This thesis deals with the structural behaviour and design of concentrically-aligned single gusset plate welded connections to the ends of steel hollow section members. Such connections are commonly found in diagonal brace members of steel framed buildings and also in roof truss web-to-chord member connections. The types of sections considered are circular hollow sections and elliptical hollow sections, with the plate either slotted and welded into the tube or the tube welded into a slotted plate. In addition, the presence (or lack) of an open slot at the end of a slotted tube connection—a fabrication method particularly favoured in North America—is evaluated within the scope of this work. Under quasi-static loading, the behaviour of the connection has been rigorously studied under both axial tension and axial compression loadings, by both large-scale laboratory experiments and numerical (finite element) analysis. To complement this data, an exhaustive review and analysis of all prior international work in this field has been made. Non-linear finite element models, validated for all 13 laboratory test specimens, formed the basis of an extensive parametric study resulting in a further 891 "numerical tests" to supplement the data base of experiments by the author and other international researchers. In tension the tube failure modes of circumferential fracture (with or without the presence of shear lag) and tear out (or "block shear" failure) were clearly identified by both experimental and numerical investigations and the parameters influencing these limit states were thus clarified. As a result, new unified design provisions for such connections in tension are presented, that are shown to be a significant improvement over current international design provisions. In compression, the tube failure mode of local buckling governed throughout the connection study and the influence of the shear lag phenomenon—hitherto completely disregarded by all design provisions under compression loading—has been highlighted. A new static design method for slotted end connections in compression is hence advocated, which is shown to be applicable to circular, elliptical, square and rectangular hollow sections. Guidance on the proportioning of the longitudinal fillet welds, so that these do not govern the connection capacity, is also presented. The foregoing static design recommendations, that now more truly describe the actual connection performance, allow connections to be designed in a less conservative manner. Such insights were hence extrapolated to the design of these connections under seismic loading situations. At present, slotted tube connections are popular in seismic zones but the hollow section is typically reinforced with steel cover plates to increase the net area at the critical location to avoid premature fracture under tension loading cycles. Using finite element analysis, it is demonstrated that this reinforcing practice can be avoided, for circular hollow sections, if both the tube and the plate are slotted in such a manner that the weld terminates at the tube gross cross-section. The validity of this "modified-hidden-gap" detail is finally demonstrated by means of three large-scale specimen tests under pseudo-dynamic loading.