Footing Design for Sound Barrier Wall

[tdm01]

I'm in the process of designing the foundation for a new precast concrete sound barrier wall. I've designed many standard spread footings in the past, but I'm a little unsure how to design the round "pier" footings below the posts. I'm in a high wind area so the overturning moments will be large compared to the gravity loads. I'm looking for advice and/or reference material on how to calculate the soil bearing pressures as well as design the reinforcing for this type of footing. Any advice would be appreciated.

 

[msquared48]

Sounds like your typical pole footing design to me.


Mike McCann
McCann Engineering

 

[jdonville]

tdm01,

These are designed as narrow drilled shafts with shallow bearing.

In the absence of jurisdictional (State DOT, etc.) guidance, this is how I would probably proceed:

Treat the end area of the drilled shaft as a shallow footing to resist the vertical loads.

Remember that the ultimate capacity of the soil under lateral load will likely require comparatively large deflections at the ground level to fully develop, so you will likely need to use at-rest soil pressures with Brohm's method to determine the depth you need to resist the lateral loads and/or moments.

Neglect the contribution of the top 1-2 feet of soil pressure and use a factor of safety on the resisting soil pressure of 1.5.

Since the lateral earth pressure increases with the square of the depth, this shouldn't be that big a deal unless you have poor soil conditions.

Jeff

 

[msquared48]

The AITC manual has a good explanation of pole type framing to include the footing design procedure. I have the first and fourth editions. The procedure and formulas have not changed.

Mike McCann
McCann Engineering

 

[JKW05]

2006 IBC Section 1805.7 has design methods similar to the AITC methods for pole footings.