Question: Our company is designing a steel truss with wide flange chords and square/rectangular web members. I see here in your book, “Hollow Structural Section Connections and Trusses” that rectangular webs are only permitted in overlapped K-connections. I am curious as to why they are not allowed in gap connections. Is this a hard rule, or is there simply a reduction in capacity if the rectangular webs are used in gap connections? Where would you recommend I get more information on the subject?

Answer: As you noted, the book “Hollow Structural Section Connections and Trusses – A Design Guide”, 2nd. edition, by J.A. Packer and J.E. Henderson, Canadian Institute of Steel Construction, 1997, does include connection design provisions for HSS web members welded to wide flange (I-shaped) chord members. In Table 3.4(a), it does indicate that the HSS web members are restricted to aspect ratios of 1.0 for K and N gapped connections, but 2.0 for K and N overlapped connections, when using I-section (wide flange) chord members. Research on HSS web member-to-I section chord member connections is actually very limited. In the latest international guidelines on this topic [1] – which are now a draft international standard (ISO 14346) – the range of validity for square/rectangular HSS web members to I-section chord members has now be restricted to HSS aspect ratios of 1.0 for both gapped and overlapped K and N connections, to reflect the scope of the supporting research. References: [1] IIW, 2012. “Static design procedure for welded hollow section joints – Recommendations”, IIW Doc. XV-1402-12, International Institute of Welding, Paris, France.