Replies

1. 
   woodguy99 | Sep 26, 2006 01:32am | #1

   C7x9.8

   Area=2.87

   Depth=7.00

   I (x-x)=21.3

    

   I don't know of span tables for C-sections like there are for wood beams and W-sections, but these numbers are the critical ones.

    

    

2. 
   user-203558 | Sep 26, 2006 03:28am | #2

   try efunda.com.  this site has lots of interesting and occasionally useful engineering information. work fast at this site because non-members are timed out after a few minutes 

3. 
   fairban9 | Sep 26, 2006 09:04pm | #3

   You can also try checking with your local steel manufacturer.  The steel manuals have load tables that can be used.  You just have to be careful in using them because you have to figure out the load that will be on the beam.  It's not like the tables in the building code - close but it's laid out more for the designer than the builder.

    

   Jon

4. 
   BenM | Sep 27, 2006 12:06am | #4

   For A-36 steel and a fully supported top flange, approximately for a uniform load only:

   span 10 feet, 810 plf

   span 20 feet, 200 plf

   span 25 feet, 130 plf

   span 30 feet, 90 plf

   You will have to be able to figure out your tributary loads.  You also need to look at the concentrated loads, shear, web crippling, any holes you may need, etc.

1. 
   fairban9 | Sep 27, 2006 04:10pm | #5

   The only thing I would worry about those loads is what it is used for - if it's going to support living space those will get you into a pretty high deflection (except for the 10' span) that would crack drywall.  It seems like alot of steel charts don't take that into consideration.

1. 
   BenM | Sep 27, 2006 06:32pm | #6

   You are absolutely right - deflection is Very important and I forgot to mention it.  If the acceptable deflection ration is L/360 then for a 20 ft span the uniform load is about 114 plf; for a 25 ft span it's 58 plf.  I would not go longer than that.

1. 
   Hackinatit | Sep 28, 2006 01:17am | #7

   Thanks, everyone!

   Ben, that L/360 is what I needed. The span is 17' and the beam will assist a garage door header.

   I'll go with more beam weight to get some more assist.

   Thanks again!Troy Sprout

   "Work is the curse of the drinking  classes."Oscar Wilde

1. 
   jvhannah | Sep 28, 2006 05:47am | #8

   BenM has covered load and deflection, and I have no idea whether he is right or not , but he hasn't mentioned bracing.  In most cases a beam that has load applied to it which approaches the critical load must also be braced, both top and bottom flanges, so that the beam does not rotate under load and collapse.  Note this is complicated by your specifying a C section beam which is not symmetrical like an I beam.  Thus the shear center is not located in the cross section of the beam.  Thus under the uniform load applied to the top flange is going to cause the beam to twist if it is not braced.  These braces do not need to be huge but they need to be there.  The same steel manual that will tell the allowable load will also give the braced spacing lengths.  The manual will not however tell you how big to make the braces unless it is a really nice manual.  Get somebody to find a steel manual, 9th Ed (Green Book) ASD manual, any of the LRFD steel manuals, or the new 13th Ed (Black Book) and find where to locate the bracing  and get the bracing sized appropriately.

   Good luck,   JV