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Recently I worked with Jeff Randall, rack design engineer at DP&W,
on the design of a PT rack for 9 SW230s, a fairly large array, in a
bosque (desert river corridor near the Rio Grande) location. We
predicted a 6' underground water table and were limited to a 36" by 72"
augered hole, and Jeff worked with me to define a pole length and array
max tilt angle that would work within these limitations. What I was
surprised to learn is that Jeff didn't recommend any reinforcement in
this hole. He said that he followed the standards of the monopole sign
(billboard) industry, whose signs were substantially larger sails than
our racks, and their specs on similar holes didn't require
reinforcement of the concrete. I had always thought that a minimum amount of reinforcement near the top of the hole would resist cracking that could lead to freeze-thaw expansion and ultimately a loose fit around the pole, exacerbated by seasonal wind buffeting, but apparently my concerns are unfounded. Some sort of steel is still needed to prevent rotation of the pole in the hold, but this could be short rebar stubs, a welded nub, or even holes in the pole. Allan Sindelar Kent Osterberg wrote: The need for rebar or not depends on how the pole is secured and on the shape of the footing. If you are installing a pipe in a deep narrow hole per most mount manufacturer's specifications, no rebar should be necessary. Anything else will certainly require rebar and per manufacturers' disclaimers should be designed by an engineer. For example, if the installation will have j-bolts in the concrete with the post welded to a plate held in place by the j-bolts, a full rebar cage will needed. |
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