Grade Beam

[Qrs]

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.

 

[XR250]

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

 

[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.

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

 

[dik]

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

 

[Qrs]

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...

 

[Lion06]

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.

 

[ztengguy]

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.

 

[a2mfk]

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.