Masonry Shear 1

[SteelPE]

I have an 8” masonry wall reinforced at 40” o.c. with d = 12’-10”. I am trying to use this wall as a shear wall (driving 41kips of shear through the wall). The code states fv=V/bd. Is bd based off the gross area of the wall or the net area based on my grouting requirements?

The code seems to imply it’s based off the gross requirements, but net makes more sense to me.

 

[Lion06]

The code does say it is based on gross area. That being said, I attended a seminar a few months back where some research was done showing that this is only true for the short, stocky walls that were tested. When the walls get larger, it acts more like a beam and column system than a wall. The idea was that an interim solution would be to use Anet, but this will be addressed in the 2011 MSJC.

 

[msquared48]

The "gross" area would be the total area of the masonry itself plus any grouted cells, otherwise you are including air which does not have much shear value.

Amrehein has a table showing the effective thickness based on the grout spacing. Use that effective thickness in your shear calculations.

Mike McCann
MMC Engineering

 

[haynewp]

Based on the net area including the grouted cells. I also use the equivalent soild thickness from Amrhein's tables as Mike mentioned.

 

[JAE]

Yes, based on the net area. See ACI 530-05, section 1.9.1, where it states that "Members shall be designed using section properties based on the minimum net cross-sectional area of the member under consideration..."

See also the attached tables and figures. These show the ares used for flexure, axial and shear.