Masonry Wall for Metal building 2

[ztengguy]

Designing a foundation and cladding wall (12'-0" tall, 8" masonry) and the metal building types want it cantilevered, not providing a girt for the top.

Question I have, would it be better to do 1 row of rebar in the center, say #7, or two rows of #5? What about a single row out of the footing, and then transition to 2 rows?

Just trying to make it easy to build, im sure the contractor will mess up 2 rows out of the footing.

 

[ron9876]

Brace it with a girt at the top of the wall.

 

[jimstructures]

Which metal building company is suggesting this solution? Or is the source the contractor who wants the least expensive building?

How are you going to detail the top of wall closure with the roof and allow for substantial deflections that the metal building will provide?

I suggest reviewing " Concrete Masonry Walls for Metal Building Systems" published by ICC(International Code Council), NCMA (National Concrete Masonry Association) and MBMA (Mwtal Building Manufacturers Association). They have many good details for designing masonry walls for metal buildings. Many of there suggestions would translate to precast panel walls and concrete cip walls with appropriate detailing.

Jim H

 

[ztengguy]

Eave height is about 22', so this is just a knee what of sorts. The Metal builder is Nurcor, they show a detail with "self supported masonry by others and a line load from the siding that attaches to the outside of the wall.

Sort of pisses me off, the owner asked me to do a foundation design, everything he sent didnt have any wall design, then this show. I guess I need to discuss it with him, and let him know what I think of the wall design.

As stated before, the is no girt, and was wondering what you guys thought about the original question

 

[dik]

Make sure your metal girt has deflection limitations consistent with CMU construction... can be a big problem if they are using L/90 for deflection and you want L/720 for the CMU...

Dik

 

[ztengguy]

There is no metal girt. This wall is cantilevered from the foundation.

Question I have, would it be better to do 1 row of rebar in the center, say #7, or two rows of #5? What about a single row out of the footing, and then transition to 2 rows?

 

[hawkaz]

How high is this wall? If you need to lap a #7, you would be better off with #5 each face. Also, watch your required embedment into the footing with a #7- might make your footing thicker.

 

[ztengguy]

12'-0" Wall, so Lap needed. I was trying to make it easy to put one line of #7 in the footing, and then 2-#5 each #7 location for the wall. #7 develops the bottom of the wall, #5 would be lapped.

 

[kylesito]

My opinion would be to go with 1 bar. If you have two bars, you will have to make sure the contractor staggers the laps between them otherwise you will exceed the allowable area of steel within one core.

Personally, I would place one bar at a tighter spacing...for example #5 @ 24" OC versus #7 @ 48" OC...before I would trust the contractor to get two bars in the right location with the right lap requirements.

This largely depends on how much you trust your contractors. In my area of the US, we get little QA for masonry and almost always have issues with bar placement and grouting.




PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

 

[cmbyrd77]

I would agree with "kylesito," I've seen too many times where the masons will come in and cut off the dowels because they don't line up, and then unfortunately won't even ask about epoxying in a new bar. So the "less is more" approach is always a good idea when dealing with masonry. In fact, if there is a contractor involved up front, I will usually ask if they would rather epoxy the vertical bars in. You'd be suprised how many say "yes."

 

[dhengr]

Let’s see..., a 12' high cantilevered wall (12' from grade, or from the ftg.?), 8" reinforced and grouted CMU wall, with a lateral load at the top, at least 6 - 8' of wind loading, from a metal building, which is designed to deflect 5 or 10 times more than a conc. blk. wall can tolerate.... do have that about right? The question shouldn’t be #7's vert. vs. 2- #5's vert. The question should be why the heck would you do a wall detail like that at all? How do you make a very flexible metal building work inside a very inflexible CMU wall system, like that? They really have to be totally independent of each other, or the metal building will term the blk. wall to rubble.

I’d detail your canti. CMU wall so that its inside face is a least 1' outside the outside edge of the steel frames, and resting on a continuous footing. Put flying buttresses every 8' on the outside to support the wall. Call it a cathedral to PEMB stupidity and in a six or seven hundred years it will be hailed as an Architectural Wonder and historic monument. At the top of your wall detail put a note saying “flashing from metal siding above, and out over the top of this CMU wall, by others; or by the PEMB supplier.” And, you want a sliding flashing joint at the top of your wall. Maybe they can make this a structural flashing to take the place of the girts they left out to make they system cheaper. Doesn’t sound like you should call them designers or engineers, they are just steel sellers. If they don’t like the architecturally pleasing flying buttresses, offer diagonal kickers to interior footings ever 8'. The added advantage of this wall system is when they start hanging piping and other mech. stuff on the walls, they don’t have to cut big chunks out of the flanges and web of the steel frame legs.

 

[shobroco]

Didn't hit a nerve with dhengr, did you ztengguy? It is standard that PEMB manufacturers state "self-supporting wall by others" because their deflection is intolerable by pretty well any other materials. There is either a girt or a light gauge angle at the top of the masonry wall in every case, and the ironic part is that they will gladly give you an angle to anchor to your self-supporting wall & they will fasten their cladding to it. You can actually make this work, provided that the distance to the next girt up is sufficient to allow the cladding to take the deflection, and your wall must have sufficient clearance from the frames that they don't push it out & crack it. Despite all of the things intuitively wrong with this system, there are thousands of buildings functioning reasonably well with this combination.

 

[dik]

Why not use plain masonry wall (EQ, maybe)with the wall supported by a horizontal channel or girt at the top, transferring a load to the PEMB at the 12' line... Least costly way to do it in our neighbourhood...

Dik

 

[Ron]

dhengr is exactly right. If you consider strain compatibility....it won't work! You can't waterproof something like that so look at more than just the structural adequacy...consider how the building works.

 

[ztengguy]

The wall is only at 1 end wall, so frame deflection wont be an issue. The first girt is at 13'-6" from the floor, so there isnt much load from the siding.

As for trusting the contractor, thats on the owner. My contract is with the owner to design a footing, that can be built. If the contractor cannot read plans and a tape, then he should not be building it. If he messes up, then its his dime (or owner) to correct. Im not a babysitter for them, just the engineer that will provide a build-able design.

Im not sure I need flying buttresses or diagonal kickers, the wall design is fine with the required steel. I understand the issue with Metal buildings, and owners get what they pay for. Luckily its only one end wall. The siding comes down over the outside of the wall.

As for plain masonry wall with a girt, for the 3rd time, there is no girt at the top of the wall.

Thanks Kylesito & cmbyrd77 for the advice, nice to get some feedback on my question.

 

[TXStructural]

Can you get the required flexural capacity at the wall/footing interface with a single bar down the middle? I would think that a 12 foot tall cantilever wall with some kind of thrust and/or wind load applied at the top will probably require fully developed bars near each face. You will have to resist all 22 feet of wind, so just wind gets you 20 psf x 10 ft/ft applied at the top of the cantilever, and a uniformly applied 20 psf on the lower 12 ft, gives you an unfactored, WAG estimate of 3.84 k-ft/ft of moment at the base of the wall. With centrally-located #7 bar at 2 ft on center, (jd=3") it calcs to about 30 kips per bar, or 51 ksi, before factors (and applying the correct wind values.)

Be sure you have adequate cover to confine and bond the bar to the grout. Also, be sure the dowels to the footing are hooked or otherwise fully developed into the foundation, or the wall won't actually cantilever. DO NOT ALLOW wet-setting of the dowels under any circumstance. Code requires that they be tied in place before concrete is placed (in which case, the number, spacing, and location are just details.) Wet set dowels NEVER fully develop the bar as required by code, primarily because they are placed after initial set, and they are typically not consolidated properly (since vibration to consolidate the concrete will cause the dowels to move.)

After reading more recent responses (I started typing on this last night), I'm not sure what the purpose of this wall is. You said foundation, but it is only one end and it will be covered with siding. I don't understand the intended function of the wall. Is it actually taking any lateral load from the building, or is it just self-supporting?

 

[msquared48]

Why are you making this your problem? You contracted for a "Foundation" design, which the wall is no part of.

This is extra services. Get the owner to acknowledge this AFTER you have a solution to the problem (make the PEMB designer an offer he can't refuse), and get the change in writing if you want to proceed.

The wind brade to the mainframe is the only logical answer. The PEMB owner will just have to a special design for the mainframe rather than pull the worn out rabbit out of the hat to make more bucks.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ztengguy]

Its a 12' self supporting wall, i think for some architectural appeal to the front of the building. Its got about 11" of trib area from the siding, there is a girt pretty close to the top. I dont want to ignore it, otherwise no one will worry about it, till the mason comes and trys to put it up and then I get a call sayting WTF?

Thanks for all your comments. I got it from here.