Post Tensioned Tie Rod for Nonvoided Slab Bridge
Post Tensioned Tie Rod for Nonvoided Slab Bridge
(OP)
I'm designing an off system (non NHS) prestressed solid slab bridge for a low volume road. It will have six 5' wide slab sections. I have seen details by various DOTs that use solid rods (A449) with nuts and DTIs or 1/2" dia. post tensioned tendons for transverse tensioning of the slabs. Since this bridge is going not going to be built by a contractor I am going with the rods. Is it possible to get a 30' long ASTM A449 rod? It looks like 12' is a standard stocked length.
I have also considered threading a piece of #8 rebar, but it has a much lower yield strength and is not really made to be used as tension rod.
I have also considered threading a piece of #8 rebar, but it has a much lower yield strength and is not really made to be used as tension rod.





RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
I am not familiar with ASTM A449 rods (so I can't help you with available production lengths) but if your applied prestress is too small then the expected losses due to concrete shrinkage and creep will reduce you assumed P/A to near zero.
Also, if you are stressing the rods to significant levels of stress, your stress relaxation properties may not be favorable compared to ASTM A722 Grade 150 ksi PT threaded bar.
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
This is a normal detail for these types of bridges. Per the A449 spec minimum tensile strength is 120 ksi and minimum yield strength is 92 ksi. Normally the rods are 7/8" diameter and are tensioned to 39 kips. That works out to 70% of yield strength. According to ASTM the proof load is 85 ksi which would be 51 kips for a 7/8" diameter rod.
I'm just trying to figure out if it's a good idea to spec a rod that long or what I should spec instead.
Thanks
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
Did you call Dywidag? They should have something in the length you need. You'll probably pay a premium for a small order.
There's also 100 ksi stainless rebar that's available.
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
Thanks for the help. Our state hasn't done many of these types of bridges, so I'm interested in how this turns out.
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
I would recommend you not use Grade 75 due to the low pre-strain and probable prestress losses that would be sustained.
A722 150ksi bars have a proven record, readily available, and competitively priced.
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge
Agree with Ingenuity, Stress Bar, Dywidag bar or similar due to its reduced relaxation performance.
RE: Post Tensioned Tie Rod for Nonvoided Slab Bridge