Code:
To address the technical aspect of this discussion, speaking as someone who has designed/signed/ sealed a lot of canopies and various structures for wind loads in Florida, threaded rod or any type of rod bracing would almost never be allowed to carry even small compression loading.
Under 1990's AISC code( and I believe these are still good), all members used for compressive loads must have a max slenderness ratio kL/r less than 200. Any tension member is limited to max kL/r of 300. So your rod sounds like it might just barely get by or be close to a kL/r=300.
If the dead load of the canopy does not exceed the uplift, then the rods would be subject to compression, but as they only have kL/r of 300, they cannot be allowed to go into compression. Other structural provisions must be made. Most structural engineers would laugh at someone using a threaded rod, even large diameter, as a compression member. That is not what they are made for, the fittings and so on are not designed for compression or reversed loading.
You can tie the canopy down with some members going downward, or create a fixed connection in the other members (easier said than done, and always too expensive.) The rods or other struts or even cable bracing could be used to secure it down against uplift.
Wire rope or cable-bracings are still used in many buildings, and they of course will be more slender than members. There are other code requirements for cables, and you should know something about rigging before specifiying wire rope as structural elements.
To meet code you will need to meet the slenderness ratio of kL/r < 200. A good option is to use pipe. For 9 or 10 ft, in tension only, you must use something with r > .576, such as 1.5 inch sch 40 pipe.
Forget about bracing the rods and what is covering the rod, unless it is structurally attached. If the galvanized tube covering the rod is not welded or bolted or otherwise secured, then it is not there. You could make a structural element where the threaded rod is tightened against the sleeve to make a specialty member, but this would be more used for a mechanical orfurnishings application.
The dimension of 51 ft sounds too long for just 4 rods, that is a spacing of 17 ft??
