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plywood sheathing to improve old brick building

plywood sheathing to improve old brick building

(OP)
Wondering if anyone has used plywood sheathing to improve in-plane stability of an old brick house wall.
See pic.
I have used steel moment frames and I might need to do that here too but thinking about the connection between the shear frame or wall and the masonry wall, I'm wondering if it would be easier to attach PT 2x10's to the existing brick (flat) and then apply plywood sheathing to the inside face of the 2x material.
Definitely would need to consider relative stiffness and I'm thinking it might be unlikely in this case (for the plywood to be very stiff). Usually I use steel moment or braced frames but just wondering if anyone has used interior plywood sheathing fastened to the inside face of a masonry wall to improve stiffness.
Seismic design does not usually control.
Building is long and narrow. I'll have plywood shear walls at interior locations parallel with this front wall but first interior shear wall will be 20 ft inside of this front wall.
Looking for thoughts about ease and suitability of attachment for the wood vs. steel frames.

RE: plywood sheathing to improve old brick building

How old is the building and the brick? And why exactly is this needed?

Attaching to old brick is a difficult idea, especially if you're talking often enough to have an efficient shear transfer. Are you gutting the building?

Please remember: we're not all guys!

RE: plywood sheathing to improve old brick building

I haven't seen that solution before. I'd personally be more interested in looking at FRP as a solution. Although FRP can add strength to the wall it cannot add stiffness. Although, I'm not sure the plywood would really add much stiffness either in relation to the brick.

RE: plywood sheathing to improve old brick building

(OP)
Approx 100 years old.
Yes, gutting the building including removing the brick chimney that is located about 16 feet in from the front wall.
I agree that attachment old (soft) brick is problematic but... just trying to think about plywood option instead of steel frame. Either one will have the same challenge of attachment. Seems like a board and plywood option might be better suited to working with the old brick.

RE: plywood sheathing to improve old brick building

(OP)
I'm looking at "in plane" loading only for this.

RE: plywood sheathing to improve old brick building

It's innovative and I'm sure that it would be effective to a degree. In addition to concerns about fastening to the brick, I foresee the following issues:

1) Those narrow, sheathed piers would need to be very stiff in order to shelter the masonry from load. As you can see from the crack pattern, the masonry is basically attempting to work as a portal frame. That will be pretty stiff.

2) Once you build those shear walls, they'll need to be tied down with hold downs etc. Aside from strength, you'll need a system that doesn't really have any give at the hold down. Otherwise, the masonry will pick up the load before the hold down kicks in.

3) Your 2X on the flat will be carrying axial forces, as all shear wall boundary members do. To keep them from buckling in a plane perpendicular to the wall, you'll have to fasten them to the masonry quite regularly.

4) From a code classification perspective, I'm not really sure what this system "is". Maybe check in with your AHJ before getting too far down the path.

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: plywood sheathing to improve old brick building

The cracking appears to me to be deflection/settlement cracking. The middle of the wall has moved down under its own weight. Not sure how either sheathing or moment frames would solve that.

RE: plywood sheathing to improve old brick building

Agree with Hokie.

Please remember: we're not all guys!

RE: plywood sheathing to improve old brick building

Certainly, I agree with regard to the cause of the visible cracking. However, the issue at hand here is the lateral capacity of the wall, is it not?

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: plywood sheathing to improve old brick building

Yes, but I like to look at first things first, and the cracks are not due to racking force.

RE: plywood sheathing to improve old brick building

why the cracks extending above the window siles?

RE: plywood sheathing to improve old brick building

(OP)
I will address the cause of the visible cracking separately.
For now, I want to find a way to improve the resistance to racking for this wall.
I think for stiffness reasons, I will probably try to use a braced frame (thinking about the first floor level now only), possibly made out of steel angles so they could readily be "buried" in a 2x4 stud wall that could be built against the inside of the existing brick.
The architectural plan will not accommodate a moment frame plus, I don't think I can get something stiff enough that way.
I don't expect that I need anything "special". I just know that I want to improve the resistance to racking and am trying to think of a reliable way to "grab onto" the existing brick wall with some sort of stiff frame. It does not seem to me that plywood anything will be stiff enough but am searching for experiences with something like that.
I expect that most of the attachment might occur in the corners.

RE: plywood sheathing to improve old brick building

I would still recommend looking into an FRP option as it may provide the strength improvements you need. Simpson Strong-Tie recently acquired some concrete repair businesses and offer FRP design services in conjunction with selling FRP. There has been some testing of FRP to unreinforced URM and I think could potentially be something worth investigating.

RE: plywood sheathing to improve old brick building

Any chance the building is listed in a historical register? That can seriously limit what you can do to it, including permanently attaching new materials to existing. FRP might just pop the faces off the soft interior brick, when and if it gets loaded, and is definitely not removable.

I guess my question returns, as to why this is needed. Analyzing old materials as if they were new is not a worthwhile process, as they behave so differently. If you're adding interior shear walls then I'd recommend taking a good hard look at the necessity of permanently messing with the existing materials. After all, the building has done fine for 100 years - old isn't necessarily bad.

Devil's advocate, but it's also not my stamp.

Please remember: we're not all guys!

RE: plywood sheathing to improve old brick building

(OP)
I appreciate the comments.
The building is not historically significant so they don't have too many hoops to jump thru on that front. Some "Historic Neighborhood Review" will happen but the restrictions will probably be modest. (They are removing the fire escape.)

I am very interested in the FRP product but was thinking like SLTA wrote, it might be a problem binding hard (FRP) materials to soft (brick) materials. Still, I will be looking at that.
On a semi related note, I will be "attending" a Simpson webinar tomorrow on FRP strengthening.

My counter to the argument that the building has "done fine for 100 years..." is two-fold:
#1 It depends on what one means by "done fine".
#2 A building (like everybody else) won't last forever and it is only getting closer to the eventual end...
Besides, doesn't everybody here get that look all the time?
Would anyone suggest that they continue the remodel with knob and tube wiring?

About the need,
The need is stemming from the fact that we are removing every existing interior wall AND the masonry chimney that is located about 16 ft inside of the front wall. We are replacing some walls and the new walls will be designed as shear walls however, the nearest perpendicular wall will be about 28 feet away (approximately the middle of the 16 ft wide x 54 ft long building). And as if that isn't enough, they will be adding a rooftop deck above about 2/3 of the building, presumably bearing directly above the two side walls above the existing roof.
The side walls are: 20" thick stone basement walls then 12" thick brick at one floor then 8" thick brick for the second and third floors. Floor joists are bearing on the "shelf" which is created at the wall thickness steps (except the third floor joists are bearing in brick pockets). Top of the walls are sloped from front to back with roof framing side to side and bearing on a spill plate on top of the brick walls. So, we have two parallel walls about 14 ft apart and almost 30 ft out of the ground and they are held together with floor joists bering on the "shelf" or in a brick pocket. Oh and of course I did see they have those nice metal rod ties in there occasionally. I could not see more than a dozen of them in the whole building (currently everything is fully gutted so I think I would have seen the if they were there.
Hers's a pic from the side.


RE: plywood sheathing to improve old brick building

There appears to be several areas of concern.

It appears that the rubble stone foundation wall has deteriorated and possibly that the mortar joints are failing.

There are numerous areas of cracking due to differential movement, possibly due to failure of the stone foundation. If 20" wall, then, without a footing the foundation is light for the height unless founded on very good soil. I've encountered similar height buildings on 3' or 4' thick foundation walls. A similar building in the background also appears to be in some distress.

There are numerous areas where water has penetrated the wall, and, if wood framed floors, there could be brown rot (aka dry-rot) issues. The fascia at the roof appears to have deteriorated. You can lose 30% or more of the strength of wood without any loss of weight with rot conditions.

What is the condition of the mortar joints? If repairing, make sure you use low strength, not Portland cement, mortar.

If you seal the building by adding airtight doors and windows, you may have some problems; you have to remove all sources of water. Old buildings lasted so long because they were drafty and dry and freely allowed moisture to leave. Also lifestyle changes cause a greater degree of occupancy and use of water for cooking, showers, etc.

Just some cautions... good luck.

Dik

RE: plywood sheathing to improve old brick building

I see this type of cracking in a lot of older brick buildings where the foundation, whatever the type, is compromised or weakened with an exterior crawlspace access.

Depending on the actual foundation that is there, you might consider underpinning and or pin pile and leveling. You should be able to read any settlement while walking on the first floor structure.

Mike McCann, PE, SE (WA)


RE: plywood sheathing to improve old brick building

mike^2:
One of several areas of concern. Often for that type of foundation wall, the original mortar was not as hydraulic as it should have been and has lost strength because the mortar cement has leached away... have encountered foundation walls where only sand remained.

Dik

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