concrete tilt wall chord angle
concrete tilt wall chord angle
(OP)
We are designing a large 500000SF+ warehouse. The solid concrete tilt walls are probably going to be 24' wide, 9 1/4" thick, and 40' high. It's in a low seismic area - design category B. The joists (supporting 22GA metal deck)are at approximately 6' o.c. and sit on 8"x6"x12"long ledger angles welded to steel embeds. My question(s) have to do with the chord force. First, in calculating the chord force, it can be shown that each individual 24' wide concrete panel has enough overturning resistance at 0.6D to resist the whole chord force. Does this mean that a connection between the panels at the roof can be eliminated. From talking with a couple other engineers, this actually seems to be fairly common. Second, we plan to run a continuous angle along the wall, welded to the top of the joists with say a 4" fillet weld. Does anybody see a reason that this angle should be attached to the concrete wall as well - say with a fillet weld to another embed on the top leg? Could this extra connection be eliminated if loads are given on the drawings for the joist seats to carry from the bottom of the continuous angle down to the top of the 8"x6" joist seat? Finally, if splices are needed for the continuous angle on the top of the joists (see question 1), should the angle be broken say at the middle of each concrete panel (12' from the joints) so there is a little room to stretch as the concrete shrinks to avoid diagonal shrinkage cracks. WHEW!!! Sorry about the long post. That took longer to type than I thought it would. I'd appreciate any comments.






RE: concrete tilt wall chord angle
At the connection of the roof diaphragm to the panel, you are supporting more than just the roof diaphragm shear. You are also supporting the out-of-plane wall reaction, assuming the roof deck is a point of support for the wall panel for out-of-plane loading. You will need some sort of connection to support that reaction. I think the easiest would be a deck angle unless you joist connection can handle that also.
On the lateral shear side, the shear needs to be able to reach the panel and eventually get into the foundation. If you can transfer the roof shear every 6 feet through the roll over capacity of the joist seat that's up to you. That could turn into a lot of shear every 6 feet to combine with other loads, something to look at.
ACI 318 chapter 14, 14.2.6 states that wall panels must be connected to intersecting elements, and footings. I've seen details where panels are connected with dowels to the lowest floor slab, with nothing to the footing itself, but we always provide a connection to the footing anyway. Maybe it depends on how you interpret the code and your connection detail to the slab.
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
Try checking out some of the information by the Tilt-Up Concrete Association.
http://www.tilt-up.org/default.htm
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
The connection of the diaphragm to the walls is key to get the load into the walls, and even if the tilt-up walls can resist the overturning alone, they still should at least be tied back to the slab on grade (which is also a common detail in tilt-up), but I think they also would anchor the slab on grade to the footing.
Yes, the connection to the panels must resist the greater of the two loads. You do not need to splice the angle at the joints between the panels. The angle does not prevent the walls from acting indivudually. Each panel acts individually and will likely be enough to accomodate the overturning. If not, then you can group your panels together using panel to panel connections along the vertical joints. However, you will have shear build up in the connections along the vertical joints in those panels if you do have to design them as grouped. Those forces can really accumulate.
The PCI handbook has some good examples also with sketches that go into this concept. They also include good information on structural integrity connections.
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
In addition, the wall itself has to be "stitched-up" to the diaphragm to fully transfer the out-of-plane reaction from the wall panel. 0.6D and overturning do not come into play for this load direction.
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
RE: concrete tilt wall chord angle
You need connections from your girders and joists to the tilt-up panels to transfer the load to the tilt-up panels. This more evenly distributes the load into the walls.
You may not need actual connections between each of the tilt-up panels though. If your panels can resist the overturning without uplift then then only reason to provide panel to panel connections would be for alignment purposes. For precast panels we provide panel to panel connections such that you have at least two or three per panel joint with one of the connections being closer to the top of the panel (1st 1-2ft). I don't know if it is common practice to provide panel to panel connections for alignment of tilt-up panels though. The 3rd edition of The Tilt-Up Design and Construction Manual should address the case for panel alignment I would think. If not if you do not expect to have differential bowing of your panels then you may not need any. In precast panel to panel connections are provided for several reasons: to account for un-even heating of one face of the panel due to sun (air conditioning on other face that would result in bow, bowing due to eccentric loading of joist/girders or eccentric prestressing, and bowing accidentally created by shipping or improper dunnage points for storage in the yard.
I hope that this helps to clear things up for you, and that I have not been too repetitive in my replies.
RE: concrete tilt wall chord angle