The table bracing is called stretchers. They provide lateral support. I dont know of any standards and so I have to rely on instinct and experience. In this case, especially with the massive top section, I would think that the stretchers are absolutely necessary. It's not just dragging that you have to worry about, it's also because of bodies leaning and bumping it. These stretchers could also act as a foot rest.
There are other ways of making stretchers such as making the long side with a stretcher down the middle instead of the outside framework. The next problem is designing the legs themselves to handle the stress. Looks like the original design has already done that.
I'm sure there are engineering formulas for the weight carrying, however from a practical point of view, Normal table legs are very strong. The problem is with the joinery holding them to the table top and not with the weight of the table top.
Making hollow table legs as you show is perfectly acceptable, again, vertical load strength is tremendous.
Me personally, I would have made the legs butt joined rather than mitered. Mitered joints are rarely perfect and so there will tend to be one corner that is not perfect. This could be a future problem. There are techniques for doing this correctly, though. This is just my opinion.
Tony B Retired woodworker, among other things.
"Strive for excellence and settle for completion" Tony B
Last edited by Tony B; 02-08-2016 at 09:31 AM.