MBS Foundation - Large thrusts without tie-beams or hairpins
MBS Foundation - Large thrusts without tie-beams or hairpins
(OP)
I'm currently designing a proposal for a client. Its a MBS with a (3)100'span (300' wide building) and frames are at 40'oc. As you can imagine the loads are considerable. The client GA drawings require us to avoiding tie-beams or hairpins. In addition no slab will be installed until the client finds a tenant. Additionally, the only geotech info I have is a allowable bearing pressure of 3ksf.
Question: I see the only option (at this proposal phase) is to employ a ballasted footing design that depends on soil friction. I can likely get the column baseplate low to avoid any additional moment onto the footing. IBC provides some friction coefficients. However, this just doesn't to be "enough" in my opinion. These are rather large loads and I'm trying to design with some half-hearted info on soil condition, YET stay competitive.
In normal circumstances, our company stays clear of ballasted footings. We also avoid hairpins when spans get larger than 70'. However, this is above and beyond all of this.
Thanks,
Question: I see the only option (at this proposal phase) is to employ a ballasted footing design that depends on soil friction. I can likely get the column baseplate low to avoid any additional moment onto the footing. IBC provides some friction coefficients. However, this just doesn't to be "enough" in my opinion. These are rather large loads and I'm trying to design with some half-hearted info on soil condition, YET stay competitive.
In normal circumstances, our company stays clear of ballasted footings. We also avoid hairpins when spans get larger than 70'. However, this is above and beyond all of this.
Thanks,






RE: MBS Foundation - Large thrusts without tie-beams or hairpins
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
@hokie66 - Bored piles sounds interesting, but that would require way more geotech info than I have at my current disposal. I'm also curious to the financial trade off (huge mass of concrete with ballasted footing vs. the installation of bored piles). As for the client being "wise" maybe - but the client is creating a building, but has no tenant yet. The tenant may not end up needing the flexibility being engineered here, yet the client will have paid for it. Risky, IMO.
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
In the projects I've seen drag struts they tend to be trenched soil cast grade beams (8" to 12" wide) extending from the pad footing into the building. The top bars are anchored to the footing to transfer lateral thrust into the drag strut. It is resisted by side friction on the trenched footings. Where I'm at these can be about 3' deep or deeper.
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
"We shape our buildings, thereafter they shape us." -WSC
RE: MBS Foundation - Large thrusts without tie-beams or hairpins
And note that those movements are based on a lot of empirical data, not rigorous analysis. So if one engineer says 1 inch and another says 4 inches, you're going to have a hard time deciding. I'd stay away from it.
I would not feel bad at all about assuming a conservative value for friction (.3?)and using a massive foundation. They've put a lot of constraints on your design. Concrete is heavy and cheap.
RE: MBS Foundation - Large thrusts without tie-beams or hairpins