Trench Footing

[13bob1313]

Hey. I have a PEMB foundation design, and the client want to use "trench" footings. Basically, they want mass concrete for the foundation walls and footings, no piers. The client is a general contractor and it's their PEMB building, so I'm not going to argue with them. I'm curious how anyone would approach the reinforcing? Typical PEMB loads, the footings driven mostly by uplift, the wall footings wouldn't have much load. I don't really have a basis for the reinforcing, as these could likely function without it. Any thoughts are appreciated.

 

[MotorCity]

At a minimum, I would provide 2 bars for temperature steel in the top and 2 bars for temperature steel in the bottom.

As for any flexural reinforcing, calculate the soil pressure below the footing (or above the footing in the case of uplift) and design as a grade beam spanning between columns.

 

[KootK]

As you mentioned, uplift is probably your governing case. I'd investigate how long a length of trench footing you need to engage for tie down and ensure that your reinforcing would allow your columns to pick up that much trench footing. I wouldn't rely on the flexural capacity associated with un-cracked concrete in tension here as your likely to have temperature and shrinkage cracks o'plenty.

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.