Design of Interior CMU Walls 2

[breaks]

The current project I'm working on contains a few interior non-load bearing CMU walls. I have designed the exterior building CMU walls for the wind loads described in BOCA (1999).

According to BOCA, the minimum wind pressure to design for is 10psf (1609.6) but BOCA doesn't make this clear if this load is only for exterior walls. If I design the interior walls with this force, it seems I'll have to dowel the CMU into the concrete slab (which I've never done on any previous project with the same scenario). The openings in the exterior walls aren't especially large, either.

Any thoughts or clarifications on this topic?

 

[JAE]

breaks: Couldn't find anything in BOCA similar to the UBC where they specify a minimum lateral force on interior partitions at 5 psf.

In BOCA (99) I found the following:

1. Section 1609.6 does indicate that a minimum 10 psf be applied to "components and cladding". Whether interior partitions fall under "components" seems to be the question.

2. Section 1610.3.6.1.2 requires masonry walls to be anchored to the floors and roofs that laterally brace them. Even if you are in a small seismic area you have to follow this. It provides minimum forces as well.

3. Section 2101.1.2 allows empiracle design of masonry only if you satisfy the two limitations relating to seismic and wind. Otherwise you are dumped into 2101.1.1 "engineered masonry" which refers you to ACI 530 which is basically replicated by the whole of BOCA chapter 21.

4. BOCA Section 2110.0 requires walls to be anchored in specific ways. See 2110.4 for requirements of anchorage to the structural frame. No differentiation is made between exterior and interior walls except in Table 2107.1 where the lateral support distance to thickness is specified.

So while the interior force isn't that much, you still, by code, have to positively anchor all masonry walls to your structure...either at the floors and roofs or at some max. horizontal distance.

I agree that I can't tell from BOCA if the 10 psf really applies.

 

[LPPE]

I've always been told that interior partition walls (from BOCA) need a 5 psf load. However, I have never actually researched the code to see if that is true.
One other thing - I believe there is a minimal horizontal and vertical reinforcement requirement for interior masonry walls (seismic loadings). And if I am not mistaking, there are also requirements that the tops of the walls be anchored to the floor or ceiling above.
One more thing - Again, if I'm not mistaking, there is a bit of ambiguity between the masonry code and BOCA about interior masonry walls. It may have been cleared up by now, but one code used to say one thing and the other something else. Good luck.

 

[redhead]

5 psf is a generally accepted pressure for the design of interior walls. The empirical design in ACI 501 stipulates a height, or length, to thickness ratio of 36 max.. If you are not dealing with seismic forces, then use these criteria and there is no need to dowel to the slab. A full bed of mortar is sufficient.
Under seismic conditions, an 8 inch lightweight CMU wall (35 psf) requires an equivalent lateral force coefficient of .143 to generate an induced lateral force of 5 psf.For a performance criteria factor of 0.9 and seismic hazard exposure group I, the Av can be as high as .155 without exceeding the same 5 psf. Whether the mortar bed is sufficient without dowelling in this case is a matter of opinion.

 

[breaks]

Thanks for all your input.

Matt

 

[JAE]

Just noticed on a Corps of Engineers project that we are working on - they require 10 psf lateral pressure on all interior walls.

 

[thaidavid]

breaks,

The Southern Building Code, and the IBC, both require a 5 psf minimum horizontal load capacity for interior walls. I suspect that this is to account for minimal wind loading when the windows are up, or there is a breach in the exterior walls. For the record, we always dowel masonry walls to the slab, whether interior or exterior.

David

 

[breaks]

A few notes on what we ended up doing:

Since our interior walls are relatively tall (26'), we designed them with 10 psf wind load as per the BOCA minimum. As JAE noted, it's hard to tell if this load is meant for interior non-loadbearing walls, but it's always best to be conservative. Using 12" CMU, the height-to-thickness ratio is an acceptable 26.

The interior walls are also properly anchored into the exterior walls and the roof slab. This is sufficient according to BOCA 2110.2.4, which specifies that "interior nonloadbearing walls shall be anchored at the intersection of the walls at vertical intervals of not more than 16".

Thanks again for everyone's comments!