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JSH2000 (Industrial)
9 Feb 01 16:19
I need to know for a generalized estimate "how to figure a load limit for say a W8x18 wide flange beam?
Ron (Structural)
9 Feb 01 19:39
There are generalized load tables provided in the AISC manuals.  For instance, a W8x18 (36 ksi) can carry a total uniformly distributed load of anywhere from about 12 kips to 54 kips, depending upon the span.(ref. AISC ASD Manual 9th Edition)  

There are several variables you have to consider such as the unbraced length, the span, the allowable deflection, bending, shear and axial loads (if any).  If your conditions do not exactly fit the load tables, you must compute the stresses in the beam for each condition.  An example would be a non-uniform load, a concentrated load, or other conditions.

Most libraries have a copy of at least one of the variations of the manuals.  If you are near a University which has an engineering program, you can likely get a copy of one of the manuals from their bookstore or you can order online from a variety of sources, including the American Institute for Steel Construction (AISC) at www.aisc.org

If you are considering this for anything other than estimating purposes, please get a licensed structural engineer involved.

Ron
JAE (Structural)
9 Feb 01 19:40
There is not a single amount of load that a W8x18 beam can take.  It depends upon the span and the amount of lateral bracing present along the span.

The AISC Manual (both ASD and LRFD) provides beam tables for wide flanges.  The tables provide max. uniform loads (kips/ft) for beams assuming they are totally laterally supported.  This means that there are braces attached to the beam which prevent sideways movement of the compression flange, or some type of torsional restraint.

The AISC Specifications provide more detail in calculating the maximum load for a beam with unbraced lengths.
jrmack (Structural)
13 Jun 01 2:13
If the beam is a W8x18, it comes in two stress levels now 36 ksi and 50 ksi.  Most beams now are 50 ksi.  Could you make a mistake here?  Maybe not as described above with the selection of the section because if you choose A36 you will certainly be OK if it is a 50 yield beam, but what about the connections: number of bolts, length and size of weld, copes, size and thickness of endplates or clip angles...if the beam is the right size, are you OK?  Maybe.
JAE (Structural)
14 Jun 01 1:38
The connection does depend upon the yield of the steel beam.  Primarily, the bearing of the bolts on the web holes would be the most affected by the beams steel yield and the possibility of the rupture of the web would have to be checked.

The bolt shear, clip angle bearing and shear, and connection of the clip to the supporting structure would not be affected.
Tezer (Structural)
14 Jun 01 2:12
Hello,
 I think not only the section dimensions but also the support conditions are important when considering the capacity of this section.The 'Manual' will help as well but it won`t take the conditions like e.g. fork supports into account,so the strength of the section is not the only parameter.
 Greetings from Turkey.

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