Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Minimum Composite Deck Thickness

Minimum Composite Deck Thickness

Minimum Composite Deck Thickness

Just looking for a rule of thumb for a typical 100psf corridor commercial application.  What is the minimum concrete thickness above the deck you like to use?  When there's only 2" of concrete above the flutes I kinda get worried because I've been told by other engineers not to go below 2 1/2".  Wondering if it is a valid point.  Obviously Vulcraft isnt going to list a product that wont work, but.....

RE: Minimum Composite Deck Thickness

Concrete thickness over deck and whether to use hard rock or lightweight concrete is driven by the required fire rating.

RE: Minimum Composite Deck Thickness

No rating is reqired.  Would you use the thinnest deck?

RE: Minimum Composite Deck Thickness

I have found that when fire rating is not a consideration then often the thickness is controled by the need to provide sufficient mass to minimze transient vibrations. I do not recommend less than 2 1/2". I often use 3 1/2" to control vibration. If you have composite beams with headed shear studs, you need a minimum stud height above the top of the deck of 1 1/2" plus perhaps 3/4 to 1" of cover.

RE: Minimum Composite Deck Thickness

I also agree with jike on the vibration issue with thinner decks.  Verco catalog has span tables for 2" over metal deck (for example, 4" total thickness for W2 and 5" total thickness for W3 deck).

One question: Is stud length of 1 1/2" minimum above the top of deck required by code?

RE: Minimum Composite Deck Thickness

AISC Manual of Steel Construction, Chapter I, Section 5.1.4 (Page 5-60 of the green ASD Manual) requires the stud length to be 1 1/2 above the top of the metal deck.  

Also, total slab thickness shall not be less than 2" above the top of the deck. I.5.1.5.

RE: Minimum Composite Deck Thickness

If the slab is too thin (say 2"), it will often produce a hollow sound which gives a "cheap" feel to the building rather than a solid feel.

RE: Minimum Composite Deck Thickness


I agree. I was giving the code miminums above (at least the AISC minimums). In the absence of a required fire rating, I usually use 3" above the deck, just for that reason, and vibration control.

RE: Minimum Composite Deck Thickness

Thank you for the code reference.  I also would not use a 2" over deck for the reasons you mention.  But if one was to use 2" over deck profile (as per deck manufacturers' catalogs) is it acceptable to design beams/girders as non-composite?

Another reason to use a thicker concrete is for installation of expansion anchors at hanger supports.  Many product ICC reports require 3 1/4" minimum over deck.

RE: Minimum Composite Deck Thickness

What process do you use to check for vibration of the deck itself?  I know how to use the AISC design guide for the steel, but never for the deck.

RE: Minimum Composite Deck Thickness


IMHO, it is should be acceptable to design steel beams and girders as non-composite if that fits the particular application better. A local steel erector has told me that if you have approximately 500 or less studs on a job, the savings in steel using compsite action probably does not pay for bringing in the stud welder machine, getting it calibrated for the job, and having the special inspector doing ring and bend tests.  So, for small buildings, we tend to go with non-composite beams if we can.

Good point about the expansion anchors, though be carefull of expansion anchors in an overhead application.

Loui1: Good question. I've always checked the entire 'system' ( beams, girders, deck, etc). Never the indivual elements.

RE: Minimum Composite Deck Thickness

There is no vibration check for the deck that I am aware of. The slab thickness may have to be increased to add mass to change the vibrational response of the "system".

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close