I understood most of your idea, but i didn't understand what you meant by "Then tension each turn to the desired load sequentially, temporarily locking each loaded line while you set up to load the next turn, until all the turns have been loaded."
OK awtchi, I will try to clarify by using a couple of examples.
When you put a new shoelace into a boot, you cannot just thread the lace, then pull on the ends to tighten it up, the first few eyes will tighten, but after that, the force just does not travel past the eyes all the way down the lace. This is due to the 'capstan effect' see
http://notableknotindex.webs.com/friction.html. So, we can't just thread a rope several times around the two end anchors, then haul on the end and expect all the turns to tighten up to the same tension (unless the anchor bars have ultra slick surfaces such as hard anodised Al). Every time the rope goes around an anchor, it looses force, so we have to tension every run in turn.
Let us presume, that the two anchor bars are sitting in recesses in the ends of the beam (to protect the tensioning rope from damage and abrasion.)
Take a length of rope that is long enough to pass through the beam the required number of times (n) to give you the necessary load multiplier. Start the rope with a spliced eye and slide this over one of the anchor bars. Then feed the rope down the channel in the beam, around the other anchor, then feed it back to the beginning, then around the anchor bar again alongside the spliced loop, then back down the channel, again and again 'n' times. At this stage it is fixed on to one anchor by the spliced loop, passes back and forth from end to end 'n' times around both anchor bars, and at the moment it is hanging loose - untensioned.
Now an explanation on tensioning. I was top-roping my climbing partner once when he hit a particularly difficult part of the climb and called to me to haul him up over the part that he was stuck on. I leaned forward, took out all the slack in the rope and then leaned back, hauling the rope up 6". But it wasn't far enough, he needed me to haul him up 18" to the next hand hold. With 70kg hanging on a climbing rope, they go stiff as an iron bar,and only 1/2" thick, you can't grip them sufficiently to haul that 70kg up. So what was I to do? I let him down to his previous hold, then I took a loop and tied a Prussic loop onto the climbing line, it is an adjustable friction hitch. I hauled him back up 6", then I slid the Prussic down the rope, put my hand through the loop which gave me a good grip on the rope and hauled him up another 6". I then took the slack out of the rope above the Prussic and locked it into my belay plate. I then slid the Prussic back down the rope and hauled him up another 6", and so on until he was climbing again.
You can utilise this technique of two tension points to tension the first length of rope passing through the beam. Tie on a Prussic connections (or better a VT hitch), and slide it into the channel beyond the anchor bar. Haul on the Prussic connection to tension the rope. Maintain that tension while you work on tensioning the next rope.
Go back to the starting side of the beam and find the rope that comes back from the now tensioned line. Slide a Prussic onto it and into the channel, beyond the anchor bar. Haul on it to the required tension. Maintain that tension while you work on the next length.
Go back to the exit end. The first Prussic is now doing nothing because the rope is tensioned both sides of it. Remove it from the rope (using the VT hitch makes removal much easier) and fix it around the rope now running from the line under tension at the eye end. Slide the hitch along the rope into the channel and haul on it to the required tension. Repeat this tensioning end to end just as you would tension a shoelace all the way up the lacing.
The final run of rope has to be treated differently, because this run has to be tied off. By now you should have found out how the Whoopie hitch works, it is simply a length of the rope braid, opened up and the other rope passed inside it, much like one snake swallows another. Then when the opened braid is tensioned, it shrinks onto the inner rope, gripping it like a Chinese Finger Trap. This is exactly the way the eye splices are made.
EDIT : see the termination tensioning in the next post.
And there you have it.