Steel Girder Bridge - Field Splice Repair 2

[KennyRogers]

I had a good one come across my desk and I can’t find any articles, papers, etc regarding a similar issue so I figured I would ask this group. During painting of a bridge, the guys in the field came across some pack rust between the lower girder flange and the splice plates. The pack rust wasn’t horrible, but the plates need to be replaced.

Is there a method or process that would allow the removal and replacement of the lower splice plates without shoring the girders? Have you ever encountered a repair like this?

We came up with a few ideas, but I am very wary about getting any slip at the connection while it’s apart which would preclude us from re-installing the new plates. We confirmed that the strength at the field splice should be adequate for dead and live load absent the lower plates. The web splices are not considered slip critical, so it is hard to determine what kind of load-slip capacity it might have.

Thank you for any input you may have.

 

[bridgebuster]

See if the attached is of any use. It's from a bridge job I did in 1998 (it's also in metric). The bottom flange plates of the splice had to be replaced because they were distorted in a fire. I used tie rods to hold the stringer together while the plates were replace. It must have worked the bridge is still standing.

BTW - regarding the pack rust on your bridge. Do you have any special procedure for treating it? I have a project that's being bid soon - a lot of built up floorbeams with pack rust. I'd like to compare notes.

 

[KennyRogers]

Thanks for the reply. Yes we had thought about a system like the one you show, however the owner is very adamant about staying out of the contractor's means and methods.

One of the concerns I had with this method was punching new holes in the tension flange and what I would do with them after the work was completed. Normally we fill them with bolts (compression flanges), however the owner would not allow us to have holes like this in the tension flange.

In terms of the pack rust issues, we looked at products like Termarust, however we don't have a lot of experience with these. The situation we are facing, is that these products might protect the bridge for ten years, however we need to bridge to last 20 years and then this corridor is going to be completely re-constructed. The existing plates lasted since the late 60's, so we remove the plates, clean and prime, install the new plates and then re-paint this will get us the remaining life we need.

I should mention that we are planning on thickening up the plates and chamfering the corners of the plates to better meet the LRFD sealing criteria. These particular plates utilized a staggered bolt pattern and the corners had a fairly large edge distance.

I have also seen guys blow out pack rust with an air hammer. The real key to preventing and stopping pack rust is to have adequate clamping force in the joint.

 

[hokie66]

Your owner needs some education. Bridgebuster's solution is workable. "Staying out of the contractor's means and methods" is a fine sentiment, but does not always work. It is better to have a fallback if the contractor can't come up with an acceptable approach, and now you have one.

 

[dhengr]

KennyRogers:
I agree with Bridgebuster and Hokie. Obviously, you should unload the beams as much as possible during the repair. I think something like Bridgebuster’s detail would work, but you’ve kept dimensions, span lengths, loads and forces a secret, so its tough to tell. An alternative detail would be turning the WT’s 90̊, so they are parallel to the girder; make them much longer and provide the two rods on either side of the WT webs. The back end of the WT could be clamped ( C clamps, maybe?) to the girder flange, eliminating the holes. The shear force, parallel to the girder flange would be taken by a welded shear block on which the WT pushed against. These shear blocks would be cut off and the girder flange ground smooth.

 

[Qshake]

Nice suggestion, bridgebuster.

I agree with hokie66 on having a solution on paper and yet still permitting the contractor to review, and submit, anything they feel will be betrer for their means and methods. And that the contractor's work would be submitted to the engineer for his/her approval. There is absolutely nothing wrong with this and I've see it done for many years that way.

dheng - I believe the intent of the forum is to present ideas which the original poster will need to vet through for his/her self and determine if the details work or not for their situation. I would not want to know the specifics of this situation (spans, forces, loads, etc) and have someone else do the calculations and make a statement for all to see and use or mis-use.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[dhengr]

Qshake:
I wasn’t actually thinking of doing the OP’ers. calcs. or vetting of the repair method for them. But, with so little info. about the scale and forces involved in the problem; that is, the difference btwn. a 8' deep plate girder and W36 girder, Bridgebuster’s or my solution might or might not be particularly practical. I was offering a solution to reduce the reactions and eliminate the bolt holes in the bot. flange which the OP’er. seemed want to do.