I'm going to disagree with the following posting: If the tower is bolted to galvanized pipe that is embedded in concrete of which a significant amount is in contact with soil, you have a "concrete-encased grounding electrode" which is hard to improve upon. It is not likely that a ground rod would be worthwhile, since damp concrete (concrete in intimate contact with soil at grade level) is a fairly good conductor, and such a footing or foundation has hundreds of times the surface area of a ground rod.
I have read Ericsson specs for cellular tower installation in that disagrees with the previous statement. Standard concrete without conductive enhancing materials can crack, pop or crumble if subjected to a direct lightning strike if ground rods are not properly installed. The water contained within the concrete will vaporize instantly causing the concrete to fail. There are types of conductive concrete mixes or additives that can be used, but the most common practice is to use a ground rod from each leg with a copper wire bonded to each tower leg. Our mfg building at work is made from steel I-Beams into concrete. I have noticed each I-Beam has its own ground connection. The strap is bolted to the beam about 1" above the concrete, then disappears into the concrete, and suspect there is a ground rod going into the soil beneath the concrete piling, but that's just a theory, as I dident see it before the mud was poured. Ed N3SDO
