HAIRPINS & TIE RODS 14

[sigma1]

Lately I have been reading very interesting threads about "PEMB Foundation Design". For small buildings the lateral loads can be handled but for large buildings it can be a dificult task for someone with little or no experience in this area. ASCE/SEI offers a seminal sometime in January 2008, but how much can you learn at a
web-seminar?

Is there a book or manual other than the "Butler Manual", which is not available, that provides some tenchical information and details on how to design and detail these foundations?

Any information or help will be greately appreciated.

 

[DaveAtkins]

sigma1,

Are you saying you want dowels from the foundation wall into the slab on grade instead of a hairpin? It could work, but you would have to transfer the thrust force horizontally along the top of the foundation wall, which would result in a lot of horizontal rebar in the top of the wall.

DaveAtkins

 

[shin25]

sigma1,

I see that your horizontal thrust is in fact factored. If I am not missing the point, to handle this amount of thrust you need about 5-#4, 60 ksi rebars in the active region of the footing. But, as you start to move away from the column towards the center of the slab, this requirement will gradually decrease. This is due to the fact that more and more area of conrete from the slab will take part in resisting the thrust. If you are concerned, you probably can allow only 3*sqrt(f'c) tension in the concrete. If you consider this then, you need only about 300(+) sq in of floor area to resist this thrust, considering 3000 psi concrete.

If you are considering the weight of the footing to resist the uplift then, you may need to use service uplift to size the footing.

 

[sigma1]

Let's assume tie beam (concrete grade beams) are used.

What happens to the grade beam when the thrust force is not there, or it is very low, and the beam in reality is a long concrete column under compression.

Should the beam/column be designed for the full length or can someone assume the soil and the slab above are providing lateral stability?

 

[shin25]

Most of the time, the compression force that these tie beams experience is probably nothing compared to their cross sectional size. Frequently, these tie beams will be cast monolithically with the floor slab. Due to all these factors the tie beams may be considered braced for its full length.