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Grade Beam

Grade Beam

Grade Beam

(OP)
I have a grade beam supporting a new masonry wall. The grade beam spans 20ft between helical piers. Obviously, I have designed the grade beam to support the vertical load from the wall, but does it also need to be sized for 1/2 the wind load (or seismic out of plane force) on the wall?

The lateral system is composed of X braces, so it is not the main lateral system, but because only 1/2 the wind will go into the diaphragm, does the other 1/2 need to be accounted for in this manner? I believe it does.

Or could I justify that the resistance from the soil/slab will resist the load? The grade beam is 3'4" deep...
I'm more interested in the theoretical answer, so I will know how to design it in the future. Do you guys look at this?

Thanks.

RE: Grade Beam

Depends on how much of the grade beam is below grade.

RE: Grade Beam

I suppose this starts a thought process down the road of designing/calculating all your footings for the 1/2 the out of plane lateral loads as well... It is this logic I would second that it depends on how much soil is resisting the grade.

If you are taking 1/2 the lateral and dumping it into your grade your vertical helical will not have any capacity for this
(unless battered), so lets hope it doesn't resist laterals :)

RE: Grade Beam

Generally lateral loading on the grade beam is resisted by soil pressure and/or slab on grade. Can you use arching action for the masonry wall, else you may be taking quite a 'hit' due to the vertical loading, in particular if it's a bearing wall.

Dik

RE: Grade Beam

(OP)

Quote (EngineeringEric)

I suppose this starts a thought process down the road of designing/calculating all your footings for the 1/2 the out of plane lateral loads as well... It is this logic I would second that it depends on how much soil is resisting the grade.

That's along the lines of what I'm thinking about. My grade beam is completely under grade. I would assume the soil pressure/slab could resist this. I'm wondering if this is a routine check for most engineers or gets overlooked by engineering judgment...

RE: Grade Beam

I have never checked a grade beam to span horizontally for wind load as you've described. I've always had a slab-on-grade at, or near, the top of the grade beam to resist that force. If I didn't have a slab-on-grade, I would do a quick check of the passive resistance of the soil.

RE: Grade Beam

Do you always tie the slab on grade to the grade beam? Most times we designed it to float. Soil pressure is the best resistance unless tied to the slab.

RE: Grade Beam

I would analyze like Lion06 said. If you have some below grade masonry, a slab on grade, and the footing is case against the soil, you have quite a bit of soil resistance. I would analyze like a mini-retaining wall. My gut says you will be fine.

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