×
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

Diaphragm Chord Force Transfer

Diaphragm Chord Force Transfer

Diaphragm Chord Force Transfer

(OP)
I’ve got a 520’ x 270’ warehouse with CMU shear walls only on the sides (spaced 520’ apart).  All roof framing members span front to back (with intermediate beams).  The back of the building is continuous CMU but the front of the building is mostly storefront and has several offsets (as large as three feet).  Consider wind blowing at the back of the building, what is the customary way to transfer diaphragm chord forces across the front of the building at the offsets?  Do I ignore this?  Do I add diagonals at the offsets?  Do a add members parallel to the back wall that "span across" the offsets?  

RE: Diaphragm Chord Force Transfer

Assuming that I understand the roof diaphragm geometry, and that you are talking about a plywood roof diaphragm, maybe it would be easy to just run a row of solid 4x blocking and a Simpson CS continuous coil strap across over the roof sheathing.  A CMST12 is good for 9.235 kips.  Only comes in 40' lengths, so you would have to lap.  I generally specify a tight nail spacing at ends and laps, with a larger nail spacing in the field.  I don't know why you couldn't have two or more rows of blocks and straps if needed.  What I like about this solution is that the chord is at the diaphragm level where it belongs, not down at the bottom of roof framing level.

Regards,

Jim Emanuel, S.E.

RE: Diaphragm Chord Force Transfer

Have you considered the possible need for an expansion joint in the 520 foot length?

Regarding the offsets, if the outer most member is discontinuous (at offsets) then use the 1st continuous member across all offsets as the chord. The members outboard of the chord will just go along for the ride.

RE: Diaphragm Chord Force Transfer

I have had a similiar problem.

I set a row of columns just inside the offsets, and ran joists  between the columns. The joists were set on a cap plate to the column so that their ends were only seperated by a small gap, then anlges ( with vertical leg turned down)were welded accross the gap to the top chords of adjacent joist shoes. This made a continous chord.

I used a joist loading diagraphm to give the joist supplier the necessary chord forces he needed to design the joists for.



RE: Diaphragm Chord Force Transfer

(OP)
Thanks everybody.  Just to clarify - the roof is steel beam, bar joist and metal deck.  And I do have an expansion joint.

RE: Diaphragm Chord Force Transfer

If you don't have a continuous chord member behind the offsets, I would add angles between the joists to create a continuous chord.

DaveAtkins

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