Soil Pressure + Wind Shear

[MindofBarca]

All,

I am designing the precast podium level of a commercial building (underground parking - retail - apartment living). The EOR has provide two types of lateral loads at the foundation level; 1.) Out-of-Plane Earth Pressure + Soil Surcharge & 2.) In-plane wind shear loads. The foundation walls have a cont. cast in angle which is being welded to a steel embed (with studs) inside our hollow core.

My question is: For my steel embed design, do I have to take an interaction of both of these forces acting simultaneously? We typically try to space our embeds 4' to 8' O.C. When I run the interaction of these two forces I am needing plates at 2' on center for our 12" hollow core and around 1' O.C. for our 8" hollow core. Which just seems so wrong, but I can't think of any other ways? The loads were provided to us as service level loads, I am factoring each of the loads by a 1.6 load factor.

Any help is greatly appreciated!

Thank you,
jReck

 

[JAE]

I would simply follow the prescribed load combinations from your applicable code.
In the US it would be ASCE 7.

For LRFD these include both soil and wind shear in a few combinations (H and W).

In reality - the soil lateral load is always with you and the wind load, when it occurs, would put both there at the same time.

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[KootK]

Nutty results excepted, I agree with your approach. The earth pressure will be pushing when the wind starts blowing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MindofBarca]

Thanks for the quick replies JAE and KootK. Both provided the answer I was dreading to hear Seems like the right thing to do, just seems like so many plates and so much welding. But hey, what can you do right!?

Thanks guy!

jReck

 

[JAE]

Is the earth pressure pushing INTO the hollow core? If so do the plates really resist that or is there a grouted joint between the end of hollow core and the wall to take that load directly into the planks?

If so then the embed plates would really only resist the wind load correct?



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[KootK]

A couple of additional thoughts:

1) If you contact the EOR and let them know that the connection spacing is going off the rails, they might be willing to work with you to reduce the demand. I know I would. Certainly, it seem highly unlikely that fire truck level surcharge would be acting in concert with peak wind/EQ loads etc.

2) Obviously, there is a great deal that I don't know about your building. Often times, however, the bearing details are such that the basement walls can push against the planks in direct lateral bearing. Perhaps, with some consideration given to stiffness compatibility, you can argue that some of the earth pressure loads make their way into your diaphragm via that route without adding to the burden on your embed plates.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MindofBarca]

Not sure if the links below will work or not, but I have attached 2 pdf pages sent directly from the EOR. It appears there is some type of block with a grouted gap between the hollow core and the soil. If we can make this assumption then I guess you are correct. I wonder if I still need to take the soil pressures into my floor diaphragm then?



[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1440605387/tips/1620CENT_TOFWALL_OUT_OF_PLANE_REACTION_i2ybo1.pdf[/url][URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1440605397/tips/9_1620_CENT_LATERAL_Conc_podium_shears_pocist.pdf[/url]

 

[JAE]

Well if there is a block/grouted condition in that gap then the earth pressure DOES get into your diaphragm but perhaps DOES NOT go through your embedded angle connection.

If there is equivalent soil pressure on the other side of the building then your hollow core is simply under compression. If the earth is on one side only, then this earth pressure will be
transferred into your diaphragm and then taken across the diaphragm to the resisting shear walls on either side.

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[KootK]

If we can make this assumption then I guess you are correct.

Nah. The stem of concrete in that gap looks to only be about 2" wide. And you'd need some vertical rebar running up through it somehow. And the weld plates are likely to be the stiffer load path anyhow. I`d stick with your original plan.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.