Helical Piers for Solar Canopies

[NortPE]

We're doing solar arrays on parking lot canopies, similar to gas station canopy. Proposed foundations are 14ft deep x 36"diameter reinforced concrete piers, exposed 3feet above grade. Helical piles aka "screws" would save a lot of time.
I'm confident that screws can be designed for the vertical load and wind uplift, but concerned that the top of the screw and/or bottom of the canopy column would need protection from car bumpers, but More important would be the bending moment at ground surface with lateral wind load.
Has anyone been doing this for solar or gas station canopies?

 

[KootK]

As you probably know, screw piles can handle some modest lateral loads (shear / moment). The capacity is not huge though. If a 36" diameter pier is what was required before, it's hard to imagine that you'd get an equivalent resistance from the screw piles.

As for the car impact, you could probably cast some concrete around the tops of the screw piles and the bottoms of the columns.

You could use a group of screw piles with a cap on top but that would surely be more costly than the single concrete pier unless schedule is the driving factor.



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.

 

[Brad805]

We have, but you need some geotech information to model the soil and determine the amount the structure will sway. LatPile is the common tool most geotech's use, but a simple soil spring analysis can also help to determine if it is feasible.

 

[haynewp]

We have used helicals for smaller cantilevered structures using pile caps and groups of vertical and battered helicals to resist the shear and moment. The helical piers were requested for schedule reasons rather than using concrete piers. The deflection from a single pier from the shear and moment that would translate up through the structure was unreasonable and I can't see anything other than a pile cap and a group of vertical and battered helical piers working for such a canopy.

A helical mfr such as Torcsill (

http://www.torcsill.com/)

can help with the group deflection calcs when provided the soils report if you decide to do this, but I probably would use concrete piers in this case.