ICC Approves Deflection Limits Proposal
May 4, 2012

by Ellen Rogers, erogers@glass.com

A code change proposal to the International Building Code (IBC) that concerns deflection glazing limits, S78, submitted by Thomas S. Zaremba, representing the Glazing Industry Code Committee, was approved as modified today during the International Code Council (ICC) hearings taking place in Dallas.

According to the proposal, “Section 1605.2 of the IBC provides load combinations using strength or factored load design while 1605.3 provides load combinations using allowable stress design. For wind load determination, ASCE 7-10 is now based on strength design and ultimate wind speeds. Conversion to allowable working stress (nominal) loads is accomplished by multiplying the factored wind load by 0.6.”

The proposal notes that the original reduction of 0.7 in footnote (f) in earlier editions of the IBC was changed during the last cycle by multiplying 0.7 and 0.6 to get the 0.42 factor in the current code. “The added sentence to the beginning of the footnote is a clarification to use nominal loads for wind used in allowable stress design to determine deflection which corresponds to the use of the 0.42 reduction.”

In addition, the proposal notes that a second clarification was added at the end of footnote (f) “to properly restrict the use of the 0.42 reduction to deflection calculations of main structural members shown in Table 1604.3 when using component and cladding wind load and preventing users from inappropriately combining this reduction with component and cladding deflections described in footnotes (a), (c), and (h) of this table.”

The proposal was modified to add deflection requirements for members supporting glazing, and was approved as modified.

The code hearings continue through May 8. Stay tuned to USGNN.com™ for updates as they are made available.

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