How to Handle Horizontal Reaction At Column Base

[lumbee]

I am designing the spread footings for a 40' x 60' metal building. The building manufacturer cautions the foundation engineer not to forget about the horizontal thrust load at the column base. I understand how the vertical forces and moments affect the foundation design but what about the horizontal thrust load. I'm assuming the thrust load is trying to shear the anchor bolts off and also possibly putting the concrete in tension. If this is the case, what are the equations to check for this type of failure?

Lumbee

 

[tincan]

We normally use "hair-pins" for the shorter spans and tie-rods for the larger spans. The force for the hair pins are distributed to the concrete slab.

 

[lumbee]

If the column baseplate is below the slab(12&quot, do you wrap the hairpin around the column and then into the slab? If so, how do you attach the hairpin around the column?


If the column baseplate is at floor level, is the hairpin atttached to the anchor bolts directly beneath the baseplate? How is the hairpin attached?

 

[Qshake]

I may be missing something here but once we've transfered the load from the column into the concrete we need a reliable source of resistance at the soil level. As such, should the question really be what kind of load will the soil tolerate?

 

[tincan]

If the column plate is 12" below the slab, is there a foting integral with the slab (blockout for column?). The hair pins are normally placed 2"=- around the anchor bolts to allow for concete placement. Check the bolts for tension & shear.
Check your area for a pre-engineered metal building manufacturer. This is a typical detail for them. Try "Star Buiding Systems". I have used their system for several projects and found them very good to work with.

 

[JAE]

Qshake is on to something.

The foundation design that accounts for the horizontal shear can be handled in a number of ways:

1. No hairpins - the horizontal shear is a lateral force at the top of the pedestal, some distance x from the bottom of the footing. Thus, the footing experiences a moment where the stress on one side of the footing is higher than the other. This is the vertical effect. There is a lateral effect as well, where the sliding resistance must come from passive resistance of soil on the side of the footing and gradewalls.

2. With hairpins, a calculated amount of reinforcing is extended around the anchor bolts at the slab level. This effectively takes out any lateral force applied to the footing so there is not vertical, or horizontal effect on the footing itself. The hairpin must be sized to resist the lateral force, and extend into a slab far enough to be developed. Also, it must extend far enough into the slab whereby the slab will not fail in shear (imagine a section of slab adjacent to the column breaking free and sliding with the column base outward). Usually, we provide reinforcing in the slab to extend the tension to the other side.

3. Similar to 2 above, you can create an under-slab tie beam that extends all the way across the building, directly below the floor slab. This is usually a concrete trenched-type footing with reinforcing in it that is also wrapped around the anchor bolts similar to the hairpins. This is a good detail for smaller buildings and for buildings where future or planned trench drains, etc. are not anticipated across the tie. The tie can be placed a bit below the floor slab as long as you design the concrete pedestal under the column for the slight amount of bending.

 

[jheidt2543]

There were a couple of threads on this topic last year. If you do a search on "hairpins" I think they will pop up.