Tilt-up Wall Diaphragm Chord Connector
Tilt-up Wall Diaphragm Chord Connector
(OP)
I have heard, but still cannot fathom, that the roof or floor diaphragm chord for a tilt-up building does not have to be developed for the building system to work.
There has always been the dichotomy between the lateral movement of the side connectors and the rigidity of the chord connector that has bugged me, and I believe an explanation of the above could solve the dichotomy. It gets into each panel acting separately rather than one unit.
Anyone run across this? Any explanations?
There has always been the dichotomy between the lateral movement of the side connectors and the rigidity of the chord connector that has bugged me, and I believe an explanation of the above could solve the dichotomy. It gets into each panel acting separately rather than one unit.
Anyone run across this? Any explanations?
Mike McCann, PE, SE (WA)






RE: Tilt-up Wall Diaphragm Chord Connector
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tilt-up Wall Diaphragm Chord Connector
The dichotomy comes in the that I have always learned that the top connector (Chord) must be rigid, otherwise the chord force cannot be generated to keep the diaphragm intact. This is a different issue than shear collection to a drag strut.
It is hard to explain what you do not understand, but I have heard, through my son and others, that there is another way to look at individual panels to solve the issue. That thinking is what I am trying to discover.
Mike McCann, PE, SE (WA)
RE: Tilt-up Wall Diaphragm Chord Connector
RE: Tilt-up Wall Diaphragm Chord Connector
DaveAtkins
RE: Tilt-up Wall Diaphragm Chord Connector
I can envision a detail that uses a continuous angle at the diaphragm edge with 2 to 4 fixed bolts at or near the center of the panel length, and bolts with horizontally slotted holes from there to the edges of the panels. This would allow for panel thermal movement, but keep the diaphragm chord force intact through the continuity of the angle. Say the internal five feet of a 25 foot panel would have fixed holes, and the ten feet to either side would have horizontally slotted holes.
Is that a detail anyone has ever used?
If that is the case then, the chord force is never seen by the panel, only the transfer of horizontal shear to the panel.
Mike McCann, PE, SE (WA)
RE: Tilt-up Wall Diaphragm Chord Connector
1) With an untopped steel deck, I would think that the diaphragm could tolerate the small amounts of differential lateral movements between panels. You get something similar in both conventional steel and wood diaphragms where you have to accommodate localized nail/bolt slip. Obviously, one would have to place reasonable limits on the amount of tolerable differential deflection but, for common tilt up structures, I wouldn't expect this to be a problem.
2) At a floor with a composite deck, I'd have to think that your chord would be integral with the floor and you'd be forced to use a detail such as Msquared has suggested to accommodate panel thermal movement.
With the truly "chord-less" diaphragm, I essentially see the tilt up panels as an extension of the diaphragm with the the real chord being some element of the foundation.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tilt-up Wall Diaphragm Chord Connector
Mike McCann, PE, SE (WA)
RE: Tilt-up Wall Diaphragm Chord Connector
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tilt-up Wall Diaphragm Chord Connector
DaveAtkins
RE: Tilt-up Wall Diaphragm Chord Connector
In the connection we have used our panel thickness reduces from the deck bearing elevation to the top of the panel to form a ledge. They cast continuous plates into the panels that the decking is attached to. That plate along with panel to panel connections are deemed to be the chord. We build insulated panels and there are other reasons for the ledge. This did not turn out that great because of the detailing around joist pockets and the responsibility shift for the chord. It also does not save much because one just basically shifts whom is paying for the chord material and installation.
RE: Tilt-up Wall Diaphragm Chord Connector
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Tilt-up Wall Diaphragm Chord Connector
To achieve what Mike has heard seems difficult, but then again, I have reviewed buildings from the 60's that have no perimeter chord member and they have performed ok.
RE: Tilt-up Wall Diaphragm Chord Connector
Yeah, I think that we can all agree that, in many instances, a designated perimeter chord probably isn't really necessary. In one direction, I'd argue that the deck flutes could probably do the job. In the other, interior framing a bay in from the edge could surely get the job done.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.