steel framed building on piles need lateral resisting system

[johndeng]

We have a steel framed building on piles which has no lateral resisting system. we will add cross brace, but it will transfer the load to piles. we are thinking of add grade beams between the two pile caps, or install additional battered piles.
If we use grade beam, the piles will take moments, I don't know whether piles can take moments since they are supposed to take only axial loads. each pile cap has 3 to 4 piles.

 

[mike20793]

What kind of reinforcement do the piles have? How far down the pile does the cage extend? Are there any uplift piles that have rebar running the full length of the pile?

 

[steuey]

If you are already planning to add piles, you could add battered piles to resolve the base shear on the building and try to minimize any lateral in the vertical piles. Be sure to consult with the geotech engineer that has provided soil information for your pile design. If you need to spread the lateral loads out along the building, you can add more grade beams between additional pile caps beyond the cross bracing anchor points. This will give you more locations to add battered piles, or otherwise distribute the lateral forces.

 

[KootK]

If it's a low rise building, perhaps you can attach your grade beams to the slab on grade and resist the lateral load that way. It works alright for light lateral loads. If you have no existing grade beams, what currently holds up your perimeter walls? Or are your new braces in the interior?

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.

 

[johndeng]

to mike20793: these are concrete filled steel pipe piles, pile cap is like regular footing with bottom bars, and piles embed 4" into pilecap., no dowels.

to kootk: this is a parking garage, so no walls around, stair walls just separated cmu walls.

Actually the 3 supported level garage was laterally resisted by column moment connection, but we need to extend one level above, and we find all columns are shy, only good for gravity load. so we will ignore the moment connections and try to build brace system to take laterally load. so only braced columns need reinforcement. But lateral load on footing is a problem.

 

[KootK]

these are concrete filled steel pipe piles, pile cap

The piles themselves should be able to take moment then. You'd need a geotechnical engineer to figure out if the surrounding soil can however. No uplift on the pile cap to pile connection to worry about?

The grade beam and battered pile option is calling to me. I couldn't resist taking a swing at it as it could be quite elegant. No doubt there are complications that I'm not aware of.

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.

 

[johndeng]

kootk, looks great!
I only have 12" from top of pilecap to finish grade. I am thinking of putting a steel beam between the two columns at bottom to sub the concrete grade beam. But maybe I still need concrete encasement.

 

[KootK]

Send me $50?? How about a lone pile group and cap, battered or not, that can take the shear? I like the idea of keeping the shear transfer away from the existing column bases. You're not high seismic are you?

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.

 

[KootK]

And that pile group would be right below the inverted chevron joint.

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.

 

[johndeng]

Sure, you deserve it! Just how?
The idea of pile group is much better, you are a structural genius.

 

[KootK]

Ha! Way to call my bluff. Report back with a sexy project detail or two when you're done and we'll call that payment in lieu.

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.