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Hollow concrete block work as load bearing wall? 1

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fcu45

fcu45

Structural
Jul 10, 2012
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BH
Hi
We have a single story offices area inside a warehouse where the walls are made of 8" hollow concrete block work, there is a possibility that the management would ask for additional offices on the top of the existing, but could hollow block works act as load bearing walls?

My main concern is the bending moment. Is there a detail to minimize it on the supporting block work?

Regards
 
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Hollow block has been used as load bearing walls for many years. Bond beams are usually used under floor or roof joists to spread the load and provide a continuous tie. Under concentrated loads, vertical cells can be filled with concrete and reinforced. Bending can be resisted by reinforced cells.

BA
 
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Thanks dear BA

Thanks for the tie beams tip.

The issue is that the floor is already done with hollow blocks without reinforcement neither concrete filling.
And my question raised as one colleague was mentioning that hollow block can carry the additional offices floor without reinforcing nor filling.

Regards
 
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The fact that the office area is enclosed in a warehouse helps a bit. There will be no wind forces acting on the walls. Still, it might be a good idea to reinforce a few cells where concentrated loads occur. It is not easy to do, but it can be done by breaking out face shells from the existing block, placing the reinforcement and filling with concrete.

The addition of a new floor may actually help the existing wall if it reduces its unsupported height. Is the foundation adequate to carry an additional floor?

BA
 
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Are there no areas in the US where, once you account for the site class and find a spectral acceleration less than a certain amount you're allowed to neglect it? In Canada under the 2005 NBCC you're allowed to ignore it if the site specific design spectral acceleration at a 0.2sec period is less than a certain value. So for lots of northern areas and parts of the Canadian shield you can neglect seismics if your top 30m of soil are reasonable.
 
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I guess out here in California the concept of no seismic loading is just unheard of.

You guys that get to ignore it (or have it not govern) are missing all the fun...
 
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See section 2.2 of TMS 402-08, Building Code Requirements for Masonry. This is the ASD section on unreinforced masonry. But you can't use it Seismic Design Categories C thru F.
 
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It doesn't matter where you are - you should design any retrofit for seismic activities. You might want to consider constructing a Moment Resisting Frame around the building. The columns can be in line with the walls, inside the walls or on the outside. I would be very careful about asking an unreinforced CMU wall to carry both axial and lateral loads on an additional floor.
 
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Come on, everybody. We are living in an international world. At least since we are all on Internet, there is no here and there. US is not the center of the world.
 
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Are these are existing partition walls not tied into the main structure? I think your main problem could be the foundation, not the wall. If these walls were intended as NLB partitions, I wouldn't be suprised if the walls were directly on the slab-on-grade, which may or may not even be thickened under the wall.

I would never design a new masonry structure as completely unreinforced, but for an existing structure subjected primarily to gravity loads, it should work. Trying to retrofit reinforcement in this case would be a difficult and expensive endeavor for not much gain in terms of axial capacity.
 
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Hi
Thanks again for your valuable contributions although last reply was before 2 weeks :)
In case the client asks for additional floor, I'm planning to do as what Trillers said.

Thanks again and Regards
 
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