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7/1/2005
There are two parts to your question. First, Clause 14.1 of CSA Standard S16-01 reads: “No deduction need be made for fastener holes in webs or flanges unless the reduction of flange area by such holes exceeds 15% of the gross flange area, in which case the excess shall be deducted”. Mike Gilmor adds that this rule has quite a history. He reports that there were tests performed at Lehigh University in the 1970s suggesting that even when 35% was removed due to fastener holes, the section could still reach its plastic moment capacity. Currently, SSEF sponsors research at McMaster University under the supervision of Professor Sivakumaran to see if this 15% rule might be relaxed. As you probably know, holes in a flange under compression is not a problem as the holes fill up with the fastener at the limit state thus, in effect, replacing the original material. However, for flanges under tension, the clause states: "only the excess shall be deducted". For example, if you have 25% less material due to fastener holes, you only need to reduce the section by 10% (25%-15%) and, only for flanges under tension.
The second part of the question is "yes" also. OSHA in the USA requires that most joists spanning 40-feet or more, be fastened by bolts. There is a possibility that this trend may be introduced into Canada through Provincial Health and Safety Boards. The goal of such regulation is to reduce the probability that a joist will fall from its steel support during erection. The regulation shouldn't have much impact for joists over 12 m, but we hear from the fabrication and consulting communities that for smaller joists, this may mean different shoe details and/or larger flanges.
This question appeared in the "Ask Dr. Sylvie" column of Advantage Steel no. 23, Summer 2005.
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