Strengthening an Existing Hollowcore Plank Roof System
Strengthening an Existing Hollowcore Plank Roof System
(OP)
I've been engaged to look at a hollow core plank roof that needs to go from 20 PSF to 100 PSF. And probably some additional dead load too. I'd like to round up as many options as I can for strengthening. Here's what I've got so far, acknowledging that many of these options may not actually be viable for such a heavy increase in carrying capacity.
1) FRP on the bottom.
2) Steel strapping on the bottom.
3) External post-tensioning on the bottom.
4) More bonded topping on the top.
5) Parallel beams on the bottom, perhaps acting compositely.
6) A perpendicular beam line to break up the span.
7) An entirely new overbuilt roof structure shielding the plank from load.
8) Permanent sealing and pressurizing of the space below.
9) Very strong opposing magnets on the floor and ceiling below.
Any other ideas worthy of consideration? Come one, come all... Any comments on which of the above might actually be up to the task of a three to four fold load increase?
1) FRP on the bottom.
2) Steel strapping on the bottom.
3) External post-tensioning on the bottom.
4) More bonded topping on the top.
5) Parallel beams on the bottom, perhaps acting compositely.
6) A perpendicular beam line to break up the span.
7) An entirely new overbuilt roof structure shielding the plank from load.
8) Permanent sealing and pressurizing of the space below.
9) Very strong opposing magnets on the floor and ceiling below.
Any other ideas worthy of consideration? Come one, come all... Any comments on which of the above might actually be up to the task of a three to four fold load increase?
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: Strengthening an Existing Hollowcore Plank Roof System
How about rebar laid in the cores and the cores grouted with a decent strength grout? The bottom of the cores is pretty thin so the bars are in the right location in the section, and it's pretty easy to calculate capacity if you have accurate geometry.
Some of the repairs I had to do were planks that had been cut for mechanical & other openings so they were accessible from the interior of the building, but others were done by opening the ends in the exterior walls.
RE: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
Is remove and replace not an option?
RE: Strengthening an Existing Hollowcore Plank Roof System
Mike McCann, PE, SE (WA)
RE: Strengthening an Existing Hollowcore Plank Roof System
No, not without getting pretty extreme. 3, 5, 6, and 7 would work if sufficient depth were, improbably, available. Remove and replace is an option but with a some pretty steep discincentives given that it's roof over occupied space.
What are your objections? Transfer stresses? Uncontrolled cracking over the new supports? Depending on your answer, I may or may not admit to having done this previously.
@OBG/Wannabe: thanks for your suggestions. Both are easy to evaluate which is nice. If either has legs numerically, I'll pitch it.
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: Strengthening an Existing Hollowcore Plank Roof System
External PT to hollow-core planks could be challenging.
RE: Strengthening an Existing Hollowcore Plank Roof System
The seemingly simple solution is to break up the span with perpendicular beams (your #6). But you end up chasing your own tail by diverting most of the shear to regions with little or no shear reinforcement, aside from the sequential analyses for flexure and lack of existing negative reinforcement. The only method that seemed to work, with confidence, was parallel beams beneath (your #5), though even that only seemed possible by slightly lifting the planks at midspan to relieve some dead load flexure, or making the beams impossibly stiff.
As much fun as it seemed to pursue one of the strengthening options it proved cheapest and most assured to go with your #7 (circumventing the planks with an overbuild). It's very easy to confidently core the planks for putting tube or pipe columns through since the void / strand geometry is so consistent. Plus, there are a lot of unknowns as far as material properties, strand pre-tension, strand relaxation, etc that you can avoid wrestling with by going that route.
RE: Strengthening an Existing Hollowcore Plank Roof System
It never ceases to amaze me that so many people seem to think we (SE’s) can just snap our fingers and make anything work and do the impossible. So, what’s a five to seven fold (new DL + LL) increase in loading anyway; and I don’t want any additional deflection or cracking either, or much added time, labor and cost. Then, just to jerk your chain a little bit, us old older guys, just like you younger-older experienced guys, do like to see cross sections through the existing hollow core plank system, with some detail, the end bearing details, span length, plank depth, core spacing and size, etc.
I’ll go OldBldgGuy one step further. Shore the existing planks, maybe even with a little camber. Saw cut 2" wide slots, full length, in every second or third core, as needed, from above. Install PT rods/cables, harp them down at mid span, and slightly above center at the plank ends. Grout the cores full, but leave the saw cut slot/key for a final topping key. Saw cut all other cores, from above, 1" wide, into the span, however far, to pick up needed shear cap’y. Be sure any existing topping is sound, bonded well and strong enough. Pour more topping to your liking, for final section depth. Post tension the new PT cables. The PT end anchorage detailing may prove a little interesting, but maybe not too bad with nice saw cut pockets for the bearing pls. prior to grouting.
If it is a simple span, that may be something you can balance fairly simply. Plank axial loading, bearing and shear will be some conservative average of original plank concrete, new grout with good bond and the layers of topping.
RE: Strengthening an Existing Hollowcore Plank Roof System
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
But this was a case where the HC was deteriorated on the bottom and the attempt was to simply get the strength back up to where it originally was.
Adding "stuff" to go from 20 psf to 100 psf is pretty extreme and I'd also worry about the supporting members beams, columns, walls, footings.
Your option 6 could be considered but with perhaps 4 or 5 lines of perp. beams across (i.e. reduce the span by 1/5 to get a 5 fold increase in strength based on shear).
I like the remove and replace as well.
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RE: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
I assume this is an attempt to take it from roof to floor loading. Or are we talking a rooftop patio (I hate those conversions)?
RE: Strengthening an Existing Hollowcore Plank Roof System
Also, people may not like their phones and laptops getting wiped because they walked into the building.
RE: Strengthening an Existing Hollowcore Plank Roof System
Thanks for the detailed response. It's become clear that I'll need to pay a bit more attention to shear than I was planning to. I'd figured that I'd just divide up the spans in half and grout solid locally where I needed to. Of course, if the grouting needed to be not so local, then that would get pretty onerous, pretty quick.
onlyname and I had bandied around overbuild but I think that the PT suggestion is all yours. We were thinking steel. The PT might be great from the perspective of maintaining a low profile. My only concern would be the PT not sheltering the hollowcore adequately. Fine and good if the PT slab is strong enough but, if the HC cracks in half and falls down in somebody's unit anyhow, that would be a problem. Maybe dowels could connect the HC to the new PT slab.
Where it's permissible, I assume that this kind of thing is better done topside, right? Even with topping?
Ditto. Might not be so bad here though. It's a multi story 80's building. Around here that means stacked, bearing concrete/cmu at the demising walls between units. It makes for an architecturally dull building but beefy vertical structure and foundations relatively insensitive to additional weight, withing reason.
I'd post tension everything if folks would let me. If I could keep negative flexure at pres-tress under control, I wonder if straight tendons below centre would be viable. Without running any numbers, my gut feel that the hollowcore is probably already prestressed near to the "right" amount based on the cross section and adding more prestress would probably yield diminishing returns without introducing drape, either as you've suggested or through external PT.
Love it. So:
1) Shore everything,
2) Break open all of the cores.
3) Case new concrete to make a deeper, stronger composite slab.
The economics would be key to choosing between something like this or, as jayrod recommends, wholesale replacement (I hear you jayrod!).
Nailed it. Rooftop patio on a rather grand scale.
@All: For evaluation, and based on your comments, I give you #10 for consideration:
10) Throw some new precast planks on top of the old ones. Easy, quick, and probably as light as anything else. Perhaps crane issues though.
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: Strengthening an Existing Hollowcore Plank Roof System
It's unlikely you've got 100 psf in there, but you might get 50 or 60.
RE: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
it might crack the topping over the support but you can grout it up if it's an issue. Just add enough beams until you get the capacity in shear and moment you need. Putting in frp or adding rebar will magnify moment capacity but beware as it will increase the compressive stress in the compression block possibly leading to sudden failure of the floor. Also analyzing that combination of prestressed, and reinforced cross section would be very laborious unless you have some specialized software.
RE: Strengthening an Existing Hollowcore Plank Roof System
My thoughts exactly.
If you're not going to demo the HC panels then this would make sense. Gives you more depth for deflection/vibration/shear as well if you ever wanted to try to consider the HC composite with the new PT slab.
KootK, do you have any data on the following: HC panel depth, HC span, topping on HC?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
New info rolled in moments ago..
- 10" HC + 1.5" topping
- 9.8 m spans
- Structural drawings available
- Full paver system contemplated
- CMU bearing walls
- Some appetite for increasing structure depth.
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: Strengthening an Existing Hollowcore Plank Roof System
2) I would not do steel starpping on the bottom. Tried it 30 years ago on soffit a c.i.p post-tensioned slab and the adhesive of plate to concrete did not develop much bond.
1) Soffit FRP, is there not a limit to the percentage increase in capacity that CSA Standard will permit for FRP?
3) External p.t. may be problematic with developing a detail for end anchorage, etc. I stay away from p.t. wherever possible. Sounds very clever but it has its own set of issues.
4) I don't like bonded structural topping because I find that no matter how hard we try with surface prep, and with various bonding agents from cement paste to epoxy, that when we do bond tests there are some areas where the bond strength is low, sometimes very low. Perhaps if we could find a really conscientious contractor these issues could be overcome, but these days a "conscientious contractor" seems to be an oxymoron, at least among"low bidders". Bonded structural toppings are used, but they scare the hell out of me. Added to that concern is that if subject to freeze-thaw cycling (which maybe your case is not if it is below insulation), the bond line can eventually fail... I know of a parking structure repair where this happened (not one of our jobs, thank goodness).
7) An entirely new overbuilt structure seems the safest to me. Not elegant, but it is safe and predictable in its performance.
RE: Strengthening an Existing Hollowcore Plank Roof System
so there may just be some more capacity than the 20psf design load.
Granted that's just one manufacturer's literature (LaFarge) and for the depth and span there would be no lower capacity than that. Take from that info what you will.
RE: Strengthening an Existing Hollowcore Plank Roof System
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
The way we had it done was on the bottom since the bottom was fully deteriorated and the top was still in good shape.
For your condition - yes, perhaps inserting rebar into the cores from the top might work.
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RE: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
Thanks for the input Ron. Why would adding a new precast overlay only get me 20-40 psf? Seems to me I could have it designed for any load I wish with my magic, EOR specifier wand.
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: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
Dik
RE: Strengthening an Existing Hollowcore Plank Roof System
Critical and/or constructive comments welcome. Probably need to give a bit more thought to truss bracing.
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: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
Also, unless you're hanging each hollowcore you'll want to look into shear transfer of forces between panels (PCI Manual for the Design of Hollow-Core Slabs covers this).
Overall I don't like it, it just seems like not the most efficient way to do it.
I know you looked at this earlier but how come you rejected #10, overbuilding with new precast panels? A 4' x 8" HC slab untopped gets you 110 PSF. Or if you needed to go solid slab you could do 10" thick untopped. These would probably be custom but not too much more than any stock slab panels.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
I'm not a fan of it from a durability sense either. Neat idea, minimal redundancy. Leaves me with the heebee jeebies.
RE: Strengthening an Existing Hollowcore Plank Roof System
Part of my situation with this is that a few structural firms in town have already turned up their noses at this project, deeming it infeasible given the parameters involved. And they're probably right. The project team engaged me hoping that I could come up with some innovative, perhaps a little riskier than usual, solutions.
How dare you summon the devil by name in reference to my work! Just kidding. The shock value was healthy for me.
These comments lead me to believe that you may have missed something in my, clearly lacking, details. The hangers support a continuous, field assembled beam that, in turn, supports the precast continuously. It's still scary but, perhaps, a bit less scary than you're thinking. I never would have even thought to utilized plank to plank shear transfer. Even I'm not that much of an engi-cowboy.
I'll take another look at this. Some issues that you may have thoughts on:
1) I need about 200 psf superimposed, factored over a 31' span.
2) There's a desire to keep the system depth increase to 6" or less. Granted, minds can be changed by enormous cost savings. The teams already looking at a steel overbuild option which would be much deeper.
3) I imagine that I'd need to put the new planks on bearing pads of some kind to avoid interaction with the existing planks. No big deal but more depth.
4) This thread is related to this thread: Link. You're helping out there too. So, with plank on plank, the shear would still have to travel through the existing planks unless I finagle a way to get the new planks right into the existing bearing wall. And I'd have to deal with in plane shear transfer, bearing, and all the other stuff that I mentioned in the other thread. Not necessarily a deal breaker but some noodling required for sure.
With all of the prior discussion of a steel overbuild, and me not showing the tops of the trusses, it boggles my mind how I didn't anticipate that this would be confusing. Doh! Anyhow, stay tuned for #12. Considerably more difficult to communicate in a few brief sketches.
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: Strengthening an Existing Hollowcore Plank Roof System
Ah, yes, I see what you're taking about now. I was imagining discrete support points, hence the Hyatt Regency "joke". Your system seems much less scary, though now I'm wondering how you're going to feasibly cut the HC slabs continuously to install said beam.
Blarg, 6 inches and 200 PSF is no es bueno, deflection is through the roof (or should that be floor?)
I'd say you're looking at a minimum of a 10 inch HC slab to support that.
What happened to the 100 psf from your original post?
Why? New slab will be stiffer, right?
Yeah, I think you'll have a shear problem with most systems. Noodling needed for sure, but not insurmountable.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
1) Shore 'em.
2) Saw cut 'em.
3) Shove the WT up into the slot from the bottom.
4) Weld the top flange on.
Is that bad? I'll believe you if you say yes.
That was just the new occupancy load on the existing system, already designed for some stuff. And there have been some adds. New planks would need to support 30 psf roofing, 100 psf occupancy, 40 psf average snow drift, and 150 psf intensive green roof at 50% coverage. Easy peasy, right?
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: Strengthening an Existing Hollowcore Plank Roof System
No, I just didn't know shoring was an option as you earlier said the lower story was occupied.
Oh my. I see now why the others engineers bailed. Well, I still think precast prestressed or cast-in-place PT slab perhaps using the existing HC as formwork will be your best bet and getting them the system they want with the least compromises.
You probably answered this earlier but are we allowed to do stuff below the existing hollow core slab?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
Do you account for 100psf occupancy and drifting to act simulataneously? Maybe I'm a little risky but I have a hard time believing you're ever going to get both of those happening at the same time. If they ever are planning to have a soiree that would reach the 100psf level, you know damn well they'd clear the snow.
Be careful on the green roof garbage as well. The drain hole clogs and boom... density increases significantly.
RE: Strengthening an Existing Hollowcore Plank Roof System
The space below is occupied and we are allowed to do stuff below the existing hollow core. Originally, they did want to avoid interruption to the space below. The project team has accepted that may not be possible however.
I originally thought so too but now I'm skeptical for the following reasons:
1) Cutting narrow slots into the plank in which to grout seems somewhat reasonable. When I imagine how much of the top "flange" would have to be cut away in order to install chaired rebar or PT, that seems pretty onerous/unreliable.
2) Just due to the geometry, I think that a lot of the effective depth / PT drape would be lost.
3) Pre-stressing an already pre-stressed thing and trying to asses its state of stress hurts my brain.
4) How the heck do I check the plank for its capacity while it's acting as formwork?
5) Given the small size of the cores, I'm not sure that PT anchorages and their associated bursting stress reinforcing could be made to fit. If I place the anchorages up in the topping slab, I wind up with self defeating end moments that tend to push the mid-span downwards.
As usual, I've been thinking similar thoughts. And I agree with the logic completely. I thought that they might limit the extent of the patio to a 15' strip up against the roof that would either be occupied by humans or drifted snow but not both. However, are we at liberty to make that decision for ourselves under the NBCC? Drift is a permutation of "Snow", obviously, and there are specified load combinations for snow and live load acting in concert which would seem to already take this into account to some degree.
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: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
Fair enough, so if post-tensioned is out then I'd think precast, prestressed panels would be a very efficient way to go.
If this is the case then what are the available options to add supporting steel below the existing hollow core?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
Noted and perhaps soon to be exploited.
None really other than my hanger business. We can install temporary works in the space below but nothing permanent due to headroom issues.
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: Strengthening an Existing Hollowcore Plank Roof System
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Strengthening an Existing Hollowcore Plank Roof System
RE: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
Critical and/or constructive comments welcome. I almost went mad trying to figure out how to convey this graphically without staged construction details. Be gentle.
I've attached the same details as a PDF file for those who prefer to view that way.
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: Strengthening an Existing Hollowcore Plank Roof System
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: Strengthening an Existing Hollowcore Plank Roof System
Back in the late 80's/early 90's in my area there was a somewhat common precast/CIP PT hybrid system for buildings. Precast/pre-tensioned simply supported shell beams that were trough/U-shaped, about 36" wide, then PT draped within the beam shell over multipl spans, then CIP concrete.
Is it worth a revisit to re-look at longitudinal full-length saw-cutting through to some of the hollowcores (maybe 2 or 3 per 1200mm plank width) and draping PT?
With that step created at your CMU bearing wall you appear to have access for stressing.
RE: Strengthening an Existing Hollowcore Plank Roof System
I've heard of that composite system that you've mentioned. I believe that something similar is popular in some of the former colonial countries (other than Canada). Can't remember the name of it though...
I considered it extensively and came to the conclusion that I'd probably never be comfortable with it personally. I'm happy to entertain any dissenting opinions on the following, reproduced from above:
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: Strengthening an Existing Hollowcore Plank Roof System
Let me think about it some more.
How much do you know about your existing planks data, like number and type of void (eg Spancrete, Ultra-Span, etc), number and size of bottom strands etc?
RE: Strengthening an Existing Hollowcore Plank Roof System
Please do. I'm not saying that you necessarily do this but, on Eng-Tips, I have this sense that folks sometimes give "what you should do" recommendations that tend to be a bit more aggressive than what those same folks might actually do themselves, push come to shove. I know that I'm guilty of this. My answer to everything seems to be one of the following:
1) Post-tension it!
2) Strut and Tie!
I would love to know if you yourself would actually be willing to PT this thing. I sketched out the core 1:1 and stared at it for twenty minutes to ensure a proper sense of scale. Those cores aren't huge. Also, if you had the teardrop cores as below, it seems as though you'd really have to bash away at the plank to clear yourself a decent placement lane. In my neck of the woods, the cores are sometimes wittle squares. That would be easier here.
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: Strengthening an Existing Hollowcore Plank Roof System
A good contractor could retain any of the diaphragm connection reinforcement when they removed the planks. So I'd still be in the remove and replace camp.
How tall is the block wall above?
Maybe on the odd occasion, but I usually preface that with the coverall statement that I wouldn't do this but I've seen "_________"
In most cases, I only suggest what I know. That's why I don't comment of everything and have stayed away from the PT solution. I don't have any experience with PT, or at least not enough to start commenting on it.
RE: Strengthening an Existing Hollowcore Plank Roof System
How do you see that happening? It's this condition. Only bars at the plank joints which may be difficult to match exactly. In the precast replacement option that I presented, I recommended a new connection angle on the underside with fire proofing. I also recommended doing alternate planks in two stages to preserve bearing but the practicality of that is questionable too.
It's three stories of like framing above. I may need to look a little harder at finding a way to work with a temporary, half bearing condition.
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: Strengthening an Existing Hollowcore Plank Roof System
I also don't think it should be too difficult to match the H/C joints for the new planks either. Provided the current H/C planks are the nominal 4 ft wide planks that are being supplied today, I think it's reasonable that they'd be able to do what you need.
The trickiest part is maintaining the bearing for that block wall. Maybe, temporarily, you build a stud shoring wall on the inside face of the block wall, tied in to the floors above and below, and have the masonry wall tied to it as well. It puts the planks on the other side of the wall into a bit more shear load temporarily, but it would be within D of the support so I'd likely be comfortable with it.
Honestly though, I'm likely being a little optimistic on the possibility of this. I'm getting too used to letting the contractor figure out the means and methods of the temporary construction stuff that perhaps I'm losing touch with what's possible.
RE: Strengthening an Existing Hollowcore Plank Roof System
Clever. I'm skeptical that much of the axial load could be drawn out of the masonry wall into the stud wall. But maybe that's okay. My main concern would be the wall bowing out in flexure under the newly eccentric load. If the existing wall could be convincingly tied back to the temporary shoring wall (made sufficiently stiff), that might alleviate that issue.
I guess if one wanted to truly take the axial load through the shoring wall, true shoring posts could be installed and jacked up a bit.
Is this a case where you would be comfortable just handing it off to the contractor as means and methods? Maybe that's just the way to go. They do seem to have an uncanny ability to make temporary conditions work that baffle me.
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: Strengthening an Existing Hollowcore Plank Roof System
Does the owner have a contractor in mind? Do you have a contractor that owes you a favour? It's possibly time to have a discussion about feasibility.
RE: Strengthening an Existing Hollowcore Plank Roof System
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.