Bracing/support responsibility: Masonry wall repairs 2

[WARose]

I got a damaged masonry wall I need to replace (with a identical wall). It's between two elevated floors. Roughly 20' x 10' of wall. 10" CMU with brick veneer on outside. I normally have some kind of note that leaves bracing/support during construction to the contractor.....however in this case-with so much wall being replaced-I'm wondering if I can really get away with that? The wall removal won't cause any structural failure....it could disappear and the overall structure will be fine....except for the masonry above (which isn't much, maybe about 4').

So I guess my overall question here is: do I have a responsibility here as far as giving them (maybe) some type of temporary support plan (maybe a angle to act as a lintel or something during construction)? Or will the note I typically use be ok?

 

[le99]

You have indicated this is not a bearing wall, and the direct load on top is insignificant, I think it is adequate to cover by a note with an estimated maximum line load on the top.

 

[dik]

I would normally note that the temporary support was in the realm of the contractor as a 'means and methods'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[phamENG]

I agree that it can still be on the contractor, but I on similar projects where there's a significant known hazard/challenge I've called it out on the drawings.

"Contractor to temporarily support masonry above using needle beam shoring or other suitable shoring compatible with the Contractor's means and methods." Or something to that effect.

 

[MotorCity]

Unless you are specifically hired by the contractor to design shoring, it sounds like this falls under means and methods which is covered in notes. However, sometimes we will add a big bold boxed note to call the contractor's attention to our expectation that shoring will most likely be required (it may not be immediately obvious to the contractor until the jackhammers come out). We may even go so far is to provide a "suggested" sequence or shoring plan but note that the final plan is by the contractor.

 

[bones206]

I take a multilayered approach, to minimize the chance of something being missed and to emphasize the responsibility of the contractor to own the shoring design:

1) general notes stating the general responsibility for shoring and temp. bracing, etc

2) specific notes for specific items to be shored/braced

3) sometimes a cartoon arrow on a detail or section, indicating the general location and orientation of shoring, with a label such as "SHORING BY GC (SEE NOTE XX)". I try to keep it cartoony and vague, rather than suggest using certain types of props or shoring towers, etc.

 

[dik]

Any time I encounter an issue that I don't think the contractor can reasonably handle, I generally address it.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[WARose]

Good thoughts Bones.

 

[bones206]

A few weeks ago I got some construction photos from a GC. Immediately noticed they had demo'd a CMU bearing wall beneath some HC planks without any shoring. Literally 3 guys standing under the plank in the photo. I think the grouted keyway joints were the only thing keeping the plank from dropping. My drawings had general notes and specific notes telling them to shore the plank, but no big red cartoon arrow on any details in this instance. I think those big cartoon arrows might be the best attention getters because notes are not necessarily being read. Same principle as IKEA assembly instructions I guess...

 

[SwinnyGG]

If the masonry above is that small, it may make the most sense to just strip it all as opposed to trying to short what's currently to remain. 20x4' of veneer is less than one day of the mason's time to re-install. Food for thought.

If there's some other reason the existing veneer must remain, I agree with others that ultimately it's a means & methods scope, but if there's a method preferred by the EOR a note on the drawing is helpful to the contractor.

 

[WARose]

[red]New Question:[/red] This is sort of getting on a tangent....but I don't think it is worth a new thread: anchoring/developing/lapping the new rebar to the old. Hilti comes to mind....but I'm not sure if I've ever used Hiltis to develop reinforcement in masonry. In reinforced concrete, I've seen people chip away the existing bar, thread it, then use couplers to connect the old to the new. But I don't know how feasible that is for masonry. Any ideas?

 

[SandwichEngine]

I'd check with your insurance company.

I remember watching an AISC video years ago and some in the class began asking about how the system would be erected. The instructor, who I remember as being a highly respected and well known structural engineering authority, said that it isn't up to the structural engineer to come up with a process. When the person asking the question continued on, saying something about feeling it was a responsibility, the instructor told him to check his insurance because shoring isn't usually covered by E&O insurance.

Wish I had more details but I've always remembered that advice.

 

[bones206]

I believe mechanical rebar couplers are permitted by the masonry code, but I'd have to check the specific requirements. Could also try to have the demo contractor leave a length of the existing bars projecting from the remaining wall segments so you can lap with the new.

 

[WARose]

I believe mechanical rebar couplers are permitted by the masonry code, but I'd have to check the specific requirements. Could also try to have the demo contractor leave a length of the existing bars projecting from the remaining wall segments so you can lap with the new.

That's what I am thinking bones. But leaving enough rebar uncovered to thread vs. lap......we are talking a lot more for the latter than the former. So I was leaning towards the former.

But then again: how big of a deal is that? (I.e. is it possible or much more labor intensive?)

 

[bones206]

Threading the in-situ bars might be impossible. The threading machines I've seen are like the size of a small shop lathe. I have not heard of portable threading machine small enough to maneuver onto an existing dowel, but they may exist.

Easiest for install might be a set-screw type coupler like Dayton's "Bar Lock" system.

 

[WARose]

Easiest for install might be a set-screw type coupler like Dayton's "Bar Lock" system.

Great suggestion. Now the only worry is: can they get the grout cleaned off good enough to make that happen. (It appears to me it depends on getting between the ribs.)

 

[Enable]

100% you can clean the bars well enough. We do it all the time in restoration where we pour slabs against existing, or tie into CMU foundation walls, etc. You can get those bad boys to shine better than new! The general procedure is to chip and then sand-blast. In the air that might be a bit of a hazard in terms of debris but if that is of concern aggressive wire wheeling should also do the trick.

IMHO I would be more concerned about deformation of the bar where chipped (rather than general cleanliness) affecting the integrity of mechanical couplings. Very often we nick or damage bars at the chipping location due to the hammer striking the bar. The concern increases as the size of hammer increases so if you intend to use mechanical couplers you'll want to specify 7lbs electric hammers or something of the sort.

As a fallback we often field weld splice bars in restoration. A couple months ago I did the same for new grouting of CMU above existing where used angle iron + welds after exposing 6" of existing bar. I can post the detail if you'd like.

 

[WARose]

Thanks Enable. How do you word all that on the drawings? I've been struggling with that (in my head). "Clean them bars." Crossed my mind....but that won't cut it.

 

[OH_PA_AISC]

My standard practice is to specify that the party(ies) preforming the demolition is/are directly responsible for any and all temporary shoring. Additionally, provisions of ASCE 37: Design Loads on Structures During Construction are to be strictly followed.

 

[Enable]

Not much is usually said on the drawings since industry practice for such things is relatively well-known (around here). Typically the note is something to the effect of "keep & sandblast existing reinforcing steel".

For a contractor who wasn't so experienced you could add something indicating your intention to use mechanical couplers and state that it is the responsibility of the contractor to ensure their compatibility. So something like

"Contractor to keep at least 8" of existing reinforcing steel protruding from block to remain, and clean via sand-blast or other suitable mechanical means to facilitate install of xxx coupler per the manufacturer's technical literature. At a very minimum reinforcing steel shall be cleaned of ALL concrete / grout particulates at the splice location"