Messages and Online Forum Q&A

Re: Beam Spans

From: info@builderswebsource.com
Category: Structural Beam Design
Remote Name: 63.198.181.43
Date: 27 Apr 2001
Time: 05:27 PM

Comments

Generally, more information is required to properly calculate the beam specifications, such as:

1) Total expected live load in PSF.

2) Total dead load (based on type of floor finish materials as well as any interior partitions, ceiling loads, point or distributed loads from the roof).

3) Roof material and snow or wind loads (if imparting forces on the floor due to point loads).

4) Allowable deflection (typically length/360 for a floor).

Once these parameters are known and the tributary area computed, it is possible to calculate the minimum recommended beam size. Since your roof is using trusses, there is likely minimal roof dead load transferred to the floor, but this depends on the exact configuration of the roof and any load-bearing partitions which transfer load to the floor.

However, we ran a simple example (which may or may not apply to your specific conditions). We assumed a beam span of 18 feet and a tributary length of 12 feet (half your total floor length of 24 feet). This assumes the beam is in the center of the 18x24 structure, with floor joists connected to the beam on either side. With a 40 psf live load and 10 psf dead load, the beam needs to be approximately 8x16 in either Douglas Fir or Hem/DF Larch or Eastern Species Grade #1. This is a massive beam and you may find that a glulam or microlam is cheaper and of more uniform quality. The beam should be securely mounted with heavy-duty steel post/beam connectors at either end. The post should heavy-duty and securely anchored to the foundation. Please note that you must consult a licensed structural engineer to do a proper load calculation for you. These numbers are for example purposes only and may not account for all important factors relating to your specific project.

Click here for Beamchek, an excellent software program ideal for computing exactly this type of beam, including built-up beams made from 2x material. Below is a sample of the input screen:

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