W8x15 Composite Steel Beam

[NFExp]

We have designed a floor system using a W8x15 composite steel beam. We have ran the numbers and the beam is adequate.

Does anybody know why the Composite W Shape Table 3-19 (pg 3-189) in AISC13 starts at a W10. I just want to make sure that I'm not missing something and that a W8x15 is acceptable.

 

[Lion06]

One of the principals at my firm said (partly kidding) that if he ever saw a composite W8 on someone's drawings, they would get fired!

At those small sizes, it might be cheaper to throw more steel at it than to make it composite.

 

[NFExp]

I understand that using a W8 for a compostite beam isn't ideal, but I have a special case. I just need to know if using a W8 is prohibited by AISC.

 

[nutte]

No, it's not prohibited. Whether or not you should be fired is another question.

The problem lies in connecting the beam to the support. It will have a high shear reaction, and very little depth to get a connection (shear tab, clip angles) in the beam web. You might wind up having to make the reinforce the section, making it deeper, so that you can get a deeper connection in. This is expensive, likely more so than using a deeper beam. This is why AISC doesn't put W8s in these tables, to discourage their use in these applications.

 

[Lion06]

One other thing I would check is the flange thickness. Don't the studs require a minimum flange thickness? A W8x15 is very light.

 

[slickdeals]

The code says that the diameter of the studs should not be greater than 2.5 times the flange thickness, unless welded over the web.

We have a very small margin for error in installing studs on this beam

 

[jike]

Agree, you can burn thru the flange if it is too thin and welder is not directly over the web.

 

[dik]

So what type of studs do you use with a 2" slab <G>...

Dik

 

[PMR06]

Watch your deflections too...

Will the beam be shored during construction?

 

[pjaway]

I asked AISC about min flange thickness and this is how they responded........"The AISC Specification does not address shear stud weldment requirements. However, the required base metal thickness is specifically addressed in Section 7.2.7 of AWS D1.1:2002. When welding through base metal (no decking), the base metal shall be no thinner than 1/3 the stud diameter. There are different requirements when welding through metal deck. Refer to AWS D1.1 or contact AWS technical support for questions pertaining to their Code (website at

http://www.aws.org.)"

When dealing with typical 3/4" dia studs, the flange thickness should be at least 1/4".

 

[DHKpeWI]

For what it's worth, I would just use a heavier W8. Adding the studs adds tremedously to the cost.