×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

"R" Value of LW Concrete on Metal Deck

"R" Value of LW Concrete on Metal Deck

"R" Value of LW Concrete on Metal Deck

(OP)
Could someone plese provide or point me in the right direction to find the R value for a 3" metal deck with 3 1/4" of lightweight conrete on top (6 1/4" total thickness).  Thanks!

RE: "R" Value of LW Concrete on Metal Deck

The R-value for the sandwich can be determined from adding up the individual resistances.  Refer ASHRAE fundamentals Chapter 25 (2005).  This also has the tabulated values summarised below.  You also need convective surface resistances, which will vary according to still or moving air which I leave for for you.

Lightweight concrete varies, but for typical 100lb/ft3 density you can use around 5 BTU.in/h.ft2.degF (or 0.7 W/mK).  This ranges from 2 to 9 (0.3 to 1.3) with increasing density.

Steel is generally 26.2 BTU/ft.degF (or 45.3 W/mK).

RE: "R" Value of LW Concrete on Metal Deck

Be careful.  I can't remember for sure but I think Resistances don't just add directly.  You may have to add their inverses.  It's like parallel vs series resisances in an electrical circuit.  I always have to check before I add them up. ie. 1/Rtot = 1/R1 + 1/R2 + 1/R3 etc...

RE: "R" Value of LW Concrete on Metal Deck

R values do add directly. Rtotal=R1+R2+R3 and so on...

I had to refer to a book to remind me though. Its the heat transfer coefficients that add by using inverses.

Ed

www.engineerboards.com

RE: "R" Value of LW Concrete on Metal Deck

if there are parallel members of the construct, you get the situation where you might need to add the resistances in parallel too.  Like in a typical wood framed wall, you might have series resistances in wall finishes, and parallel resistances in the core insulation and framing.

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!


Resources