A couple weeks ago, there was a news story in the NYC area concerning the collapse of a billboard structure in Brooklyn along the LI expressway. I believe it was a 20x60’ face full flag monopole, 12 years old, at least 60’ HAGL. It apparently was put in the ground using the “bolt cage” foundation method. Basically, during a period of very high winds, the bolts at ground level ripped out of whatever they were attached to (witness heard the popping of the bolts coming out), and the entire structure fell over.
What I’m wondering is, what determines which foundation type is used? I would think a deep direct embedment would be safer for a structure of this type, with this level of potential wind stress? Is it a cost or equipment access issue? Rock issue perhaps? Just curious. In my market, I see the majors using bolt cage construction mainly on very low height bulletin structures, or poster structures.
Are bolt cages used because it’s easier to take the structure down if the lease expires? Just bring in a crane, unbolt it, and leave the rest in the ground?