Temporary suspension of block wall
Temporary suspension of block wall
(OP)
Does the temporary suspension needling of an existing 8" block wall (which extends about 7') above the needling beams, as shown in the attached, need something to prevent the needling beams from lateral buckling of the compression flange? What is the usual practice in this regard?
The needling beams are to be installed at 3 foot centres. The load on each needling beam is about 1200 pounds. The reason for the needling is that the suspended slab on which the wall currently is supported, needs to be demolished and repoured, due to corrosion damage of rebar and concrete delamination top and bottom of the relatively thin slab.
There are numerous active electronic communications wires and cables attached to the face of the block wall, and that is the reason that the wall is not just demolished and rebuilt.






RE: Temporary suspension of block wall
Would it make sense to instead use a channel on each face parallel to the wall, less hangers but through bolted to slab instead of adhesive. Each pair of channels could replace ten needles - seems like it would be much less work.
RE: Temporary suspension of block wall
Looking at the detail, is it not possible to through bolt the threaded rods to above? I am cautious/wary of adhesive anchors in this type of scenario.
RE: Temporary suspension of block wall
1) Welding end plates to the needle beams.
2) Bolting plates to the end plates that extend a foot or so above the needle beam top flanges.
3) Attaching the hangers to the top of the plates in #2.
Another option would be to use square HSS needle beams with, obviously, no propensity to laterally torsionally buckle.
For what it's worth, my gut feel here is that you're just fine as is.
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: Temporary suspension of block wall
Is the upper slab currently being supported by the existing wall? If so, how much deflection will occur when the support is removed and the slab is carrying its own dead load plus seven feet of masonry wall?
BA
RE: Temporary suspension of block wall
First let me say that this is a partition, not a bearing wall, so the loads are quite small. My bad for not mentioning this in the original post. 8" hollow block partition wall at 45 psf x 7.5 feet high x 3 foot needle beam spacing = 1012 pds per beam, plus some allowance for all the wiring etc, say 1500 pounds max. Two hangers each end of each beam gives about 400 pounds per hanger. Why the shoring engineer's drawing shows 1" diameter hanger rods is a mystery to me, unless I am missing something. I believe that there is a deflection space at the top of he wall, but I will double check. If there is no deflection space, then perhaps some creep will have occurred and some added load may be on the wall...but how much added load would be hard to determine, and not sure if should design for that...
I too would prefer to use mechanical anchors for hangers. Adhesive anchors are too prone to workmanship issues, not cleaning the hole properly is a chronic issue. Although they are needed in some cases where edge distances etc are an issue, this is not one of those cases.
The span of the beam is not correctly shown on the shoring engineer's drawing, because the hangers must be located much farther out from the wall to clear the various things projecting out from the wall. The span will probably have to be more like 12 feet ±.
If I understand the proposal correctly about bolting channels to the wall, that is something I too had been initially considering, but it is not practical because of all the electrical items mounted on the wall (and running vertically top to bottom) that cannot be readily moved. It is the communications etc. for the entire superstructure. Also, the idea of thru bolting to the slab above would penetrate into the offices above (something that would not be well received; no pun intended).
To Kootk and BAretired, among my favourite people on the site, thanks for clarifying that it is an end torsional restraint issue. That was my gut feeling as well, although I did not express it in my post.
Suppose instead of welding the plate to the bottom flange of the beam (as shown on the shop drawing), it were welded to the top flange, would that solve the end torsional issue? That would involve no more materials, and no more work and no change in the beam size. The top flange would have to be checked bending due to the moment caused by the force times the distance from the weld to the flange to web fillet, but the loads are quite small.
RE: Temporary suspension of block wall
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: Temporary suspension of block wall
RE: Temporary suspension of block wall
You could run a small channel, say a c6 or c8, flat along the tops of the w8's with a little weld to each - then maybe add a kicker or two up to the slab. At 3ft on center you wouldn't need much to provide torsional restraint by tying one to the next - maybe could even come up with something in cold formed.