Torsional Moment - Footings

[slickdeals]

Just wondering on a Sunday morning, if there are procedures for designing a spread footing for torsional moment?

Imagine those cantilevered signs on the sides of roads. They have biaxial moment (due to gravity in one direction and wind in the other). Also wind will produce a torsional moment.

It appears that the footings can develop torsional resistance from lateral bearing on the sides. Will the coefficient of friction at the bottom provide a restraint to torsion? Are there ways to quantify this?

 

[ToadJones]

I'm guessing that this would be more of a "check" after designing the footing. I can't see this being a controlling factor, no?
Would one bother to design reinforcing for the torsion?
Interesting topic.

 

[Lion06]

Toad,
Yes, I've just "checked" the already designed footing for torsion. I've never added reinforcement for it, either.

 

[csd72]

Well, as far as the footing is concerned it wouldnt really be torsion as such rather a series of radial compression struts akin to the spokes of a bicycle wheel. As long as the torsion is adequately transferred into the concrete and the soil resists this by passive resistance then I would think there is much else to look at.

 

[a2mfk]

First of all Slick, on a Sunday AM in S Florida you really should not be wondering about torsion in footings....

Those road signs, traffic lights, etc. on the interstate and toll roads are supported by drilled shaft reinforced concrete piles, and torsion is a factor and must be designed for. My experience was it is more of a geotech problem, spiral stirrups usually take care of the torsion. This was discussed recently on another thread, if you need that type of foundation FDOT has a free Mathcad program on their website.