Brick Veneer on 4-story wood bldg 4

[gpcivil]

What are some opinions on supporting brick veneer with a wood backing? This building is around 45' tall with brick veneer. Code seems to allow brick to span from the foundation upwards of 30' before needing a shelf angle. Has anyone fastened a steel shelf angle to the exterior wall studs with lag bolts to support the masonry?

 

[DonPhillips]

If it helps, here is what 2304.12 Commentary states:

"It is common for wood structural elements to support
masonry and concrete construction. When properly designed,
taking into consideration long-term deflection,
wood can adequately support these products. The limitations
on wood supporting masonry and concrete are
recommended by that industry. Masonry and concrete
are brittle materials, which do not tolerate movement.
Wood is hygroscopic, meaning it changes dimensions
as a result of absorbing or releasing (drying) water.
When improperly detailed, dimensional change in wood
can result in damage to masonry and concrete.
The exceptions provide some relief. Flooring and roof
coverings meeting specific thickness criteria may be
supported by wood. The wood must be designed to
carry the weight of the material. A strict interpretation
would prohibit wood piles from supporting buildings
containing masonry or concrete components; an exception
permits this. Likewise, brick veneers are permitted
to rest on foundation walls constructed using the permanent
wood foundation system. Lastly, glass block can
rest on wood floors, provided consideration is given to
deflection and shrinkage."



Don Phillips

http://worthingtonengineering.com

 

[dik]

Don... good post...

just a minor clarification: hygroscopic doesn't necessarily mean there are dimensional changes; with wood, there are... just means that it can absorb/absorb water from surrounding air/environment...

Dik

 

[dik]

should read absorb/adsorb

 

[mrengineer]

Any opinions on my interpretation of IBC and ACI 530?

 

[structuralaggie]

Yea, I think stack the brick and move on. It is done all the time.

 

[jechols]

mrengineer,

I believe you violated the code if you didn't do the rational analysis and if you exceeded thirty feet or whatever the limit stated in the code is. I had to look at a building where several years (8-10 years I think) after construction bricks started popping off the building and hitting the sidewalk below. Luckily no one was injured. I discovered the relief angles had been installed directly on top of the brick below. Now this was a 10 story concrete frame building. The brick was being crushed as the building shrank/brick expanded. Also the masons decided not to put in any brick ties about 3/4 of the way up, big hole formed there.

J

 

[concretemasonry]

mrengineer -

How often do you go back to look at problems that have a long term potential?

The brick expansion is not a typical moisture wet/dry expansion/contraction contraction. There is an irreversible long term expansion that is masked by moisture early in the life of a structure.

Dick

 

[structuralaggie]

I think that if an angle was installed with a quarter inch gap as described somewhere above that you might eventually have the same problem you just described. Wood shrinkage perpendicular to grain can be significant over 4 stories, certainly more than a quarter inch.

 

[mrengineer]

I agree with structuralaggie. On more than one occasion I have seen problems associated with the ledge angle condition (most often inadequate soft joint thickness below the ledge angle). Not saying never use ledge angles, just that I would not bother in this instance. My "rational analysis" per ACI 530 (6.2.1) for a 4 story wood building would be to take a close look at the shrinkage of the wood frame and do the proper detailing (control joints, engineered wood members to minimize cross-grain shrinkage associated with dimension lumber, brick ties that accomodate vertical expansion of brick etc).