Attaching small canopies or awnings to existing brick veneer.

[Ron247]

I have 2 issues I'd like to get some opinions on. I have these 2 conversations all the time with architects.

1. I design small canopies and awnings for 20 psf roof live load unless they are cloth covered (we have only 5 psf snow). Basically, if you can stand, lean a ladder against or in any way support a person on the item, I design for 20 psf. Architects claim that other engineers do not do that, even though they can never tell me the names of these engineers. The picture below is the most recent request. This is 3' wide and 29' long. As I pointed out, if someone had to clean this, they would have to lean a ladder against the edge. The more the ladder is sloped, the more they vertically load the outer edge of the awning. So, do any of you use a lighter live load than 20 psf other than snow loads that are higher?

2. Also in this same request, they want to anchor to an existing brick veneer only. They have no idea if any wall ties are present or if they are present, what is the spacing? In my area, it is very possible that there are not any wall ties on residential but more likely on commercial. But even when they are present, I have found a lot of buildings where the only got used when someone was watching. In any case, I never allow anchoring to brick veneer only unless this was a very light load with little chance of harm to someone. These canopies always pull outwards somewhere along the wall. The closer to the top of the brick, the more this is a concern. Again, Architects claim that other engineers allow them to anchor to the veneer only, even though they can never tell me the names of these engineers. So, do you typically allow tension and overturning type larger loads to be anchored to brick veneers only and if so, where do you get your "allowable loads" from? I allow some shear only loads at times but have never allowed anything that pulled outwards of any magnitude.

 

[milkshakelake]

Can't help with 1, because it's always governed by higher snow loads where I am.

2. I don't allow anchoring to brick veneer only; it's too much liability. I always anchor to the structure. Brick veneer might or might not have wall ties. If they do have ties, you don't know their spacing, if they'll actually be installed in field with that spacing, or their capacity. The brick veneer should be able to handle lateral wind loads over a large surface but not concentrated loads that might crack it. If other engineers are allowing anchoring to brick veneer, in reality it's likely that 99.9% of the time it's fine, but I'm not going to risk the 0.1% chance of risk to human life.

 

[msquared48]

As for #1, I would also consider icing depending on your location.

As for #2, definitely anchor to the wood framing beyond the veneer that extends through the brick veneer.

If your Architect does not like the answer to #2, ask him how much insurance he has...




Mike McCann, PE, SE (WA)

 

[TehMightyEngineer]

First drunk person who tries to jump and hang off that canopy wins a free lawsuit. I've seen similar "light" loads cause huge issues in un-reinforced brick walls.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[WARose]

[blue](OP)[/blue]

So, do you typically allow tension and overturning type larger loads to be anchored to brick veneers only and if so, where do you get your "allowable loads" from?

ACI 530 allows flexural tension in unreinforced masonry. The allowable values are pretty low (see Table 2.2.3.2 in ACI 530-02 for example; we are talking between 9 and 80 psi). Direct tension is not allowed.

I've never been too clear if this (also) applies to masonry veneer (which has it's own separate chapter). But if you look at it, it sets up similar limits on stresses.

Making these connections to brick veneer can be difficult. (As the others have noted.) It's hard to find somewhere in those joints to fit all this.

 

[XR250]

They attach canopies to brick veneer in my area all the time. I have been approached to design these canopies on a number of occasions and have turned them down for all the reasons you stated.

 

[Ron247]

Thanks everyone for the response. It sounds like I am not off by my choices.

WARose- I used to work in a college town. I found college students constantly redefine "stupid things we do".

XR250-I will turn them down rather than cave-in. I usually tell them to contact those other engineers they keep talking about that allow them to do it.

My favorite line I have heard from some architects that want me to do this and have stated it will work just fine is: "Well I guess I wasted my time on that 3-hour Structures course I took in college." Gee, we went through an entire college curriculum plus a lot of independent study when we could have just taken a simple 3-hour Structures class in an Architectural curriculum.

 

[masonrygeek]

A couple of things to add. The prescriptive requirements (veneer tie spacing, etc.) found in the TMS 402/ACI 530 veneer chapter don't assume any additional load from canopies, so you would have to use what is called the "alternative design" provisions. In that case you can engineer everything to your heart's content. Of course, not knowing the types of ties, the load capacity, the embedment depth of a nail puts everything into question.

Currently, the TMS committee is revising the entire veneer chapter. The first draft is proposing to add a provision for some applied loads for things like flagpoles and building plaques. The draft is saying a maximum vertical load of 1 psf and no more than 20 lbs vertical load in any 20 sq. ft. In most cases that would not allow a canopy attachment and the canopy attachment should go through the veneer to the backing.

 

[HouseBoy]

I agree with you and the others regarding some loading and attachment to the building.

20 PSF is a reasonable starting point (other factors may apply).

I think somewhere in the code it states that veneer is not permitted to support load other than that from the brick itself.

I insist on connecting to the structure.

Only thing I might quibble with you about is the amount of vertical load that would ordinarily be transferred to the awning by someone on a ladder. Horizontal load yes. Vertical load, I don't really think so (if the ladder is being used properly).

 

[milkshakelake]

HouseBoy - A quibble about your quibble - if the ladder is leaning on the canopy at 15 degrees from vertical, there will be a vertical component of reaction. Probably not 20 psf though.

 

[BAretired]

The reaction will be normal to the ladder, so I agree there will be a vertical component.

BA

 

[dhengr]

Ron247:
Most of the time we don’t know enough about the existing brick veneer and it certainly wasn’t designed for these new concentrated canopy loadings. What are the brick ties to the structure, do they bear any relationship to the new concentrated loads and can they transmit these loads to the structure. The brk. veneer can certainly tolerate in plane loads, both laterally and vertically, and in that respect, I think the bldg. codes are overly conservative in not allowing some amount of these, assuming good attention to ties to the structure and veneer construction in general. But, their thinking, given today’s lack of much engineering experience and judgement, and the mediocre construction of many veneers and the old…, ‘but, the code says you can…, etc.,’ if they give an inch, people will try to take a mile. The brk. veneers can take very little load perpendicular to the plane of the wall, particularly not concentrated loads either inward or outward. Any localized compression or tension perpendicular to the wall just doesn’t compute, for some range of possible loadings. The correct attachment is to open up a few bricks (remove them) at discrete locations so you can go back to the primary structure and install proper structural standoffs, then flash and infill the opening as needs-be. Remember, the Arch. who wants you to sign off on something less will be sure to forget that he ever pushed you that way when things go to hell.

 

[MIStructE_IRE]

An interesting failure mode for tension anchors in brick is the ‘drawer pull out’ effect. I have only seen it once, but if it happened with a drunk college student swinging out of this canopy (or me after the christmas party...) you won’t be thanked!

 

[disoswam]

I engineer attachment for wall signs and awnings. There are no code approved anchors for brick veneer (except maybe Hilti 270 and PROFIS only calculates glue adhesion not brick out of plane strength or ties). Since my customers all put wall signs on brick veneer I am considering attaching lightweight pin letters using Liquid Nails 950 like Walmart does on hollow CMU. Since there is no code approval for structural attachment using Liquid Nails I always specify a test to pull on the pin with 50 lb for 25 lb allowable tension. I don't know if they do the test except one time they failed inspection on a 25ga metal building where they used silicone and the inspector pulled the letters off. I would NEVER consider attaching awning to brick veneer. Always attach awning to structural wall behind the veneer. I attached a 5' overhang awning with kickers using 3/4" thd rod embedded in Hilti 270 in 12" concrete wall. Since the 4" brick had 2" air the anchors were cantilevered 6".

I have a question today about an 18' wide x 1' tall no slope awning with 5' overhang and 3 kicker rods attached to a CMU wall. The awning anchors to door lintel but the kickers may anchor to unfilled cells. They said OK to use thru bolts. I'm uncertain if the 25' tall gable wall can handle lateral loads from awning wind uplift. 150mphUlt, overhang uplift 55psfASD, 12kip.ft awning total moment, 45degree middle kicker 1200 lb compression and 1200 lb uplift. The compression on kicker anchor is balanced 5' below by awning tension on the wall. The kicker force toward the wall occurs at the same time as 28psf wall wind load.

.

 

[BAretired]

Your uncertainty is understandable. It seems unlikely that the existing wall would be adequate but it could be checked if you can find drawings.

Another idea is to use an L shaped assembly (column plus cantilever) each end of the canopy with a beam spanning between them at the outer edge of the canopy. The owner may not want exposed columns, but life is full of compromises.

BA

 

[disoswam]

My customer only installs the awning and I only tell him how many kickers he needs and how many thru bolts. So I put a note on my drawing that he needs to check with the building engineer to make sure the wall is strong enough. I don't know if he ever checks but since the awning is shown on the building plan I would think the building engineer designs the wall strong enough to hold it with wind uplift. Hopefully the building department makes sure everyone does their job?

 

[Ron247]

I would not count on everyone doing their job. The wall framing may be strong enough but the brick veneer is cosmetic generally. They generally want to lag to the brick only. I know a lot of buildings where I live that do not have any wall ties connecting the brick to the wall framing.