Dereck,
Didn't you also find that with pole foundations, that you had little or no damage where you had the re-bar "double tied" or welded in place of the standard single tie?
Yes Don but the caveat here is POLE FOUNDATIONS because the amount of concrete is so small in comparison to say a slab on grade building the extra cost of double tied are justified for the extra protection it offers.
When you get into regular sized buildings due to the scale of and number of interconnections there is no real benefit IMO to double tie or spot weld. It has been my experience with a foundation as small as say a average size home, just using single tie method can result impedance as low as 1 ohm.
But as I get older and wiser, I am less convinced that such low impedance is of any real benefit. In fact I can make a good argument having such a low impedance can actually cause some problems like high GEC return current as experienced in the ole days of a metallic water pipe system.
What is important in lightning dissipation is not the actual impedance, but rather a number of paths to reduce capacitance and inductive choking. Think if a single or two ground rod system as being a funnel with respect to lightning where the flow gets backed up at the Bottle Neck of the funnel.
Today I build mostly cell tower sites and switch centers, and with the methods we use lightning problems are non existent, or when they do cause damage is minor and usually results from loose connections. A tower site uses a lot of radials, rods, Ufer, grids, and rings, so lightning has a lot of paths to dissipate very quickly before voltage can build up to dangerous levels. Plus the techniques we use inside the shelters also contribute to the effectiveness, but that is another thread, or I should say book. :grin: