Brick Veneer - Seismic Mass

[lutein]

I am working on a building with 2 stories of brick veneer (non-structural) bearing on foundation. In other words, the floors carry no brick load. I have been researching on internet and found mixed opinions in how the brick mass being considered in seismic base shear, here are some that I found:

1. Some engineers account the full mass of brick veneer in the seismic base shear calculation and distribute the base shear vertically based on tributary height of brick mass, i.e. floor-floor height x 40psf.
The reason is that the brick will produce additional seismic lateral shear from ground motion and distribute them thru brick ties to the main structure.

2. Some engineers do not account the mass of brick if the brick veneer is bearing on foundation directly.

I am hoping to hear some more opinions from you all and hope to draw a conclusion on this matter. If you know any code section that addresses this issue, please kindly post it on this thread.

 

[MiketheEngineer]

I usually discount it based on the fact that after the second wave - it will be gone anyway.

If you have to design for it - the forces are out of sight and the cost to contain it will skyrocket the price of the building. Plywood shear walls just usually won't work.

Remember - we just want the main parts of the building standing with few if any injuries to the occupants. We are not expecting it to look brand new.

The few California engineers I have talked to also agree.

 

[larsacious]

I would definitely account for the brick. The brick veneer would not be able to stand freely during a seismic event without the back up wall.

 

[msquared48]

In that the brick has to be tied back to the walls with brick ties on a two foot grid, I always assign half the story height above and below the associated diaphragm to the seismic mass.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JAE]

The brick should be included in developing the base shear, V.

The force at each level is per the vertical force distribution forumula in ASCE 7 (for US projects).

I don't see where you can suggest that the brick will be gone and then just discount it.

 

[msquared48]

Sacrifices to the Brick God?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SteelPE]

I usually account for the mass of the brick for 1/2 the story above and below each story (pretty much want everyone else does).

I would think discounting it would be ill advised. If the brick would not be present during the second wave, might it not end up on top of someone who is outside?

 

[MiketheEngineer]

In a real significant seismic event - brick veneer walls always end up outside on the ground. There are not reinforced or anchored sufficiently.

 

[firai]

In most US jurisdictions, ASCE 7 seismic force distribution dictates, as others have described. When the brick bears on the foundation directly, it just means that the foundation will take a fraction of the lateral force, but definitely not all of it unless it is an isolated free-standing wall. I cannot see neglecting this load being justifiable either by code or by rational analysis.

Structural Design Engineer
New York, NY

 

[ishvaaag]

Life safety standard not only implies nothing falling in your head, that may happen if by design you neglect keeping afoot as much as you can the façades of the building, but free and expedite exits to the building to protect life. To ensure free evacuation ways whilst letting the façades fall maybe dearer than just modify the structure to account for the wall seismic mass.

In my view if the kind of structure is not performing to satisfy what above, you modify both façade and structure itself to ensure the proper behaviour; that may mean including a reinforcement grid scheme within the wall itself, some kind of intelligent tie system to some competent structure behind, and enough of the structure enhanced to stand the brunt of the design seismic forces.