Retrofit of glued laminated beams (post tension type)

[stock1n8r]

I am looking at retrofitting a glue lam that is over stressed and one possible solution is to use a post tension type assembly using rods as my tension chord (effectively making a large bow out of the rods and beam). Where is the best place to look for design examples? Any suggestions on how to load the new tension member?

I was going to have the beam jacked up and take deflection off the beam and then back calulate the load that would have imposed that deflection, then use this load along with additional loads that have been placed on the structure to determine the load to the rods.

 

[ishvaaag]

I think that the best way of loading the rod or cable is by screwing a nut against steel reaction plates or outfits. I would try to put such nuts at both ends of the beam or whatever tou are reinforcing. If a beam, using 1 rod or cable per side and 4 nuts would be simple and symmetrical, for in the end you will have to work at both sides.

If you plan to place the tension cable or rod somewhat down the structural element, I would likely for such disposition brace it against any lateral misbehaviour, be it from loading or impact.

 

[Sawbux]

I have done this a number of times.

Add cables or strands, harp to put upward bending to reduce the D+L tensile stress in beam. Do not tension beyond relieving of the dead load as bottom of beam in compression could buckle as it is usually unbraced full length.

Best method is to put plates around end on beam to take the cable force in compression on the end grain. I have also seen bolted connections, but sometimes needs many bolts and they tend to slip and relieve the cable tension. Also have seen epoxied dowels to transfer the cable force - less slip.