Masonry Wall - Minimum Thickness 1

[Howlyn2]

Hello All, I have read several Masonry Wall Design texts and reviewed the TMS (402-11) and IBC (2015) trying to find where the code specifically calls out a minimum masonry wall thickness. I have seen a 6" minimum thickness called out several places when using Strength Design Methodologies, but I cannot find the code reference stating this. Can you please point me in the right direction of where this is called out in the governing structural design codes?

 

[r13]

Minimum thickness is limited to material availability (brick size) and use of the wall.

 

[phamENG]

And space to reinforce it. You can't reliably get rebar and grout in a 4" wall. 6" is pushing it, but with good QC at the factory and a competent mason they can do it for relatively light loads.

This isn't a code thing, it's a practicality thing. You just physically can't do it.

 

[Howlyn2]

Thank you for your responses thus far. In a May 2008 Structure Magazine Article "Designing Tall Masonry Walls" there is an explanation for an axial load capacity limitation when the h/t exceeds 30. This is clearly shown in the TMS Code. The article goes on further though to state that the minimum wall thickness is 6 inches. I believe this would be a code requirement but neither the IBC nor TMS explicitly state this. What is the justification for the 6" wall thickness?

 

[phamENG]

Draw a 4" block based on C90 minimums. Then place your rebar in the center of the wall. It's a very thin wall, so you'll probably need more steel than you would have in a 6 or 8 inch block, so call it a number 6. What is your clear grout space? Now look TMS 402/ACI 530. What is your maximum lift height for fine grout? Now consider that your input parameters assume perfection. Most block manufacturers don't manufacture to the minimums. The closer they get to the minimums, the more chance they have of some blocks being less than minimum coming out of production, thus more waste. Also, the thinner the block is, the higher the chance they break during handling or shipping. So they balance the economy of avoiding waste product with avoiding waste in overuse. So that just reduced your space inside the block. Then think about the mortar protrusions at every joint. They're going to stick into the block a good ways. I've seen protrusions on 8" block that got in the way of rebar, so just imagine what will happen if they do that in a 4". And then who's ever seen a bar in masonry placed perfectly vertical? Even with bar holders, they're always going to be a little off.

All of this just says what I already said - you physically can't do it in the real world. The code doesn't tell you not to put a 1" bolt through a 1/2" hole, but I doubt you'd tell a contractor to do it on your drawings.

 

[r13]

Back to home, 4" for interior partition wall, 8" and above for exterior and bearing walls.

 

[masonrygeek]

When you are talking about code requirements for minimum wall thickness, you may be thinking about empirical design. In Appendix A (where empirical design now lives - Chapter 5 in the 2011 version), Section A.6.2 it states that you need a 6" wall for one story and an 8" wall for anything over 1 story. BUT THIS IS ONLY FOR EMPIRICAL DESIGN and doesn't apply to ASD or SD. As other commenters have clearly stated, you can't really reinforce a 4" block, so a 6" block may be a practical minimum. So it may be a practical minimum and not a code requirement. This is slightly different for structural clay brick, but I don't want to confuse the issue.

 

[phamENG]

masonrygeek - thanks for pointing out the empirical design side of things. OP mentioned strength design, so I didn't go there, but it's valuable to bring up. It's important to remember that a lot of rules of thumb that engineers still use (and occasionally cite as "code") are actually from the old empirical design rules.