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RE: Fire Rating

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> I have a partial garage (one row of parking)
> under the main floor of an office.  When we
> began the project, there was no need to fire
> rate the floor between the two.  Now that it
> is permit time, we have to rate the floor system
> separating the two.  My client has faxed over
> some cut sheets from the U.L. manual (I do not
> have copies of the entire manuals).  The particular
> system he chose requires a minimum floor beam
> size of W8x28.  My beams are deeper, but not
> as heavy (short span).  What is U.L.'s criteria
> for MINIMUM?  Is it depth, weight, flange size?

The following answer is from Farid Alfawakhiri, my fire expert colleague
here at AISC:


P.S. Note that the information Farid referenced in the AISC Manual gives you
UL assembly numbers. You can go to with those numbers and
get all information that is in the U.L. Fire Resistance Directory for that

Any beam of similar shape configuration would usually be acceptable provided
it has a W/D Ratio greater than that for W8x28.

W = weigh of steel member in pounds per foot length
D = perimeter of fire protection for the considered section in inches
(depends whether box or contour fire protection, also depends whether 3 or 4
sides are fire protected)

If there is concrete slab on top of the beam - 3 sides will need fire
protection. For the usual spray applied fire proofing along the contour on 3
sides, W8x28 has D = 34.2" and W/D = 0.819

For a complete explanation see pp. 2-39 through 2-48 of the 3rd Edition of
the AISC LRFD Manual of Steel Construction. Tables  1-36 through 1-53 list
W/D ratios for all common steel sections.


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