Messages and Online Forum Q&A

Re: steel beam size - final answer!

From: info@builderswebsource.com
Category: Structural
Remote Name: 63.198.181.43
Date: 03 Aug 2001
Time: 10:14 PM

Comments

Based on the previous information you provided, as well as your emails and faxed drawings, our response is as follows. (Note: all calculations were performed by BeamChek software):

Since you say that the roof load IS NOT transferred in any way to the beam, then the roof or snow load does not matter for the calculation of the beam load. However, you must be SURE that there is no roof load, otherwise these calculations will be seriously flawed!

So, assuming no roof load and only the live and dead loads from the second floor, here is the basis of our calculations and assumptions:

DEAD LOAD: 15 PSF (this is a generally conservative number which accounts for the 2nd floor weight, including carpeting, hardwood, insulation, sheetrock underneath, joists, etc.

LIVE LOAD: 40 PSF (min. code requirement)

To ensure "stiffness", we used 1/480 as a conservative figure for the beam deflection under live load conditions (1/240 for total load).

Based on the drawing you sent, the tributary area is approximately 1/2 of 22.66 feet (272 inches) * 18.33 feet.

This means that the load on the beam is approximately 453.2 PLF for Live Load and 623.15 PLF for total load (live plus dead load).

This results in a minimum steel beam size of W12x14, which means the depth is 12 inches and the weight per foot is 14 pounds. The actual beam dimensions are breadth of 4" and depth of 11-7/8". Other valid choices are:

W12x16, W10x19, W10x22 (5-3/4" x 10-3/8" deep), and so forth.

Without seeing your site first hand and the actual way in which members transfer load to load-bearing walls, these are simply hypothetical examples. Whatever you do, you must consult a licensed structural engineer who can properly analyze the structural load as well as specify the mechanical anchoring considerations. Never risk occupant safety by skipping this critical step.

It looks like there are several beam choices about 12" deep that will do the job for you, assuming that no roof load is transferred to the beam.

For example, by increasing the live load to, say, 70 PSF and the dead load to 30 PSF, accounting for the roof and snow loads, this would result (approximately) in a beam that is W14x22 min. which is 5x13-3/4" and MUCH heavier steel (22 pounds per foot). The nomenclature "W" stands for "Wide Flange" I beam.

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