welding to cut end of prestressing strand

[Prestressed Guy]

Is is permissible to weld to the cut end of a strand in a prestressed member? I have a DT that was cast without the stem bearing reinforcement and the unreinforced bearing stress is right at the limit with very little margin. I need to add a plate to the end of the stem that has reinforcement developed into the stem, but they are so narrow that this is a problem. One though was to slide a plate with a beveled hole over the end of the strand and weld it to the strand.
The concept is something like this.

 

[Prestressed Guy]

(Structural)11 Jan 23 18:45
[EDIT]
Could you put a bearing plate on the bottom of the stem and anchor it at a point farther out on the stem?

I am not sure I am seeing what you are saying. If I add a bearing plate to the bottom of the stem, it will need to be recessed into the bottom of the stem in order to not change the top of flange elevation relative to the adjacent Tees. It is difficult to get much stiffness out of flat plate unless it is fairly thick so starting point would probably be 1/2". Then it would need to be anchored into the bottom of the stem which is only 3¾"5¾" wide with a ½" strand in the center. This means that there is only 1 2 5/8" of concrete outside of the stem to anchor into. I guess that the plate could have ears on the back span so that the anchor could be into the side of the stem in shear rather than into the bottom in tension. This is starting to sound highly visible which generally gets negative comments from the Architect and owner.

 

[BridgeSmith]

I don't understand why the stiffness would be a concern for the embedded plate. It would function as a tension tie. If the embedded plate has anchors in the stem beyond failure plane of the bottom corner of the stem, and anchors within the potential failure zone, it should hold it together, in the same way the end plate in your original proposal would.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Prestressed Guy]

I don't understand why the stiffness would be a concern for the embedded plate. It would function as a tension tie. If the embedded plate has anchors in the stem beyond failure plane of the bottom corner of the stem, and anchors within the potential failure zone, it should hold it together, in the same way the end plate in your original proposal would.

I think I must be misunderstanding what you are suggesting. I was envisioning a plate attached to the bottom of the stem that would take the reaction but in order to distribute the force into a greater concrete bearing area, it would need to act as a cantilever at the bearing with a couple created by the end of the stem in compression and the back span of the plate in tension.
Can you do a quick sketch of what you are thinking? One thing to keep in mind is that this is a narrow stem section which is 5¾" wide at the base with a 1/2"ø strand in the center. See design cross section.
I just realized that I have move options than I originally thought. I was thinking that this member was cast on the 24" bed with a 3¾" stem, but it is cast on a 36" bed with a 3¾" stem and a 12" filler, so the stem width is almost 2" wider than I had in mind.

 

[Prestressed Guy]

For some reason I cannot get the cross section to upload with the previous post so will try again here.

 

[BridgeSmith]

What I'm suggesting would confine the concrete at the base of the stem, in much the same way as the end plate you originally proposed. If necessary, the embedded plate could have upturned sides that would be flush with faces of the stem.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[JohnRwals]

T think this is a kind of gray area...
But, this problem happens quite frequently in the plant.
Whenever this happened, my old company used to remake without consideration.
Personally, I would like to know how this problem can be repaired.
This is D-region and stress mechanism is complicated and unpredictable.

You may use sliding connection and add steel plate to distribute pointed load.

 

[Prestressed Guy]

This could work but the epoxy dowel bar would need to extend a minimum of ld beyond the vertical crack plane. This would need to be at least 24" into the stem rather than just an anchorage depth.

 

[JohnRwals]

I think this repair needs engineering judgement.
That's why I said I remade quite often because I was not comfortable with repair either.
Though you can weld strands, you need to tighten strands before welding, which is not easy to implement.
Unless you remake this piece, you need to minimize risk or potential failure any way.
When you drill a hole deeply like 24", how can you sure this hole is filled with adhesive completely?
As you say that the owner or GC is too sensitive to aesthetics to accept steel/concrete jacket,
there are not many options you can select without taking risk, I guess.

-JRW