Damaged Field Splice on Steel Bridge Girder 2

[strudawg]

On a bridge rehab job, a contractor recently removed the concrete deck for replacement. When sawing through the deck, they inadvertently sawed into the top plate at a field splice. The field splice is located near the point of inflection. The damage is on the side of the splice where the top flange is in compression. The damage consists of a 3" long cut tapering in depth from 0" to the depth of the top plate at the edge. The filler plate below the top plate was barely nicked. At this time, I don't have load data for the girders but for information, the girders are AASHTO M223 (ASTM A-572)steel with 1/2" x 54" webs and 13/16" x 15" flanges. The top plate is 3/8" x 12".

The Question...Short of removing and replacing the top plate, does anyone know any other suitable repair procedures. The state DOT won't allow welding in a tension flange. The damage is very close but not within the tension flange.

Thanks for your input.

 

[plasgears]

Consider a splice plate welded on the flange over the damage. If you shape the ends with two fingers like an 'H,' you will increase the shear area considerably. Of course, make the cross bar of the 'H' generous in length. Proportions: finger width A, finger length 3-4 A,apace bet. fingers 1.5 A, cross bar length 4-5 A. Back up with some basic analysis.

 

[civilperson]

Just fill the cut with weld.

 

[gwynn]

If by filler plate, you mean the plate filling the gap between the two compression flanges I see no need for any repair. It's common that this is the only connection in the compression flange.

I would ask a couple questions before even contemplating a repair.

Why is the splice there? If the top flange is always in compression it sounds like this may be a launch splice. If so, the fact it can no longer carry tension is irrelevant.

It sounds like a composite bridge with the neutral axis near the top flange. What is the contribution from the top flange to the overall bending strength? It is likely to be negligible.

There is a decent chance that the contractor got lucky and the damage has no impact on the strength of the bridge. It may be cheaper just to spec a weld repair, as civilperson suggested, than to spend the time finding out whether or not the ssplice acutally matters but if there are going to be issues with the DOT over welding than investigating whether the top plate is needed may be worthwhile.

 

[strudawg]

To answer gwynn's post, the bridge is composite with a concrete deck and the steel girders. The damage was done when removing the old deck for replacement.

The filler plate is required simply to make up the difference in thickness of the adjoined girder top flanges since the girder over the support requires a thicker top flange than the girder over midspan.

I've suggested to DOT that the contractor can use a weld repair. I'll post their reply and the final solution later.

Thank you all for your input.

 

[ChipB]

gwynn's post sounds like management.

gwynn:
Are you an engineer or a manager? Or, more likely, an engineer pretending to be a manager?
Just kidding!
Pay no attention to my recently posted question. It has nothing to do with your project located in a high seismic area (really).

 

[DWHA]

I have had many experiences with this situation. Either saw cuts or hammer dings. In my experiences, usually the state dot requires the plate to be replaced. Not because it is the only solution, but because they want to make sure that the contractor remembers the mistake and will not make it again.

 

[DRC1]

Removing a plate simply to teach a contractor a lesson is not a good idea. With the deck removed, it is highly unlikely the plate can be removed with out supporting the joint. from what I understand, the splice is in compression under only the steel framing, but when the deck is poured, assuming a composite deck,the NA moves up near the steel. Gouge and weld the cuts. Once the deck is cured, the concrete, which will be in compression, will carry most of the load across the splice, and since the splice will be near the NA at that point, there will probably be little stress in the splice plate anyway.

 

[LobstaEata]

If this splice is at the point of contraflexure as previously mentioned, then the application of load along the influence line can potentially subject this splice to stress reversal. DOT in this case would be correct in requiring that the flange plate be replaced, since welding would seriously impact the fatigue life of the bridge.

 

[strudawg]

Thanks all for your comments. I thought I'd post DOT's approach to resolving this issue.

DOT’s recommended course of action is to perform an analysis to see if there is adequate section remaining (after considering the cut plate) to carry the loads. If not, DOT will allow either of the following solutions: 1) add an additional plate, with the appropriate development length on either side of the cut, or 2) replace the splice plate entirely. Replacing the splice plate will most likely require temporary shoring of the girder.

DOT won't allow filling the cut with weld material because it results in a category "E" weld situation.

 

[LobstaEata]

Sounds like the correct approach.

 

[LobstaEata]

One additional suggestion that may offer a positive effect on the cost of this repair is that shoring may not be necessary at all and here's why DOT might go along with it.

If the splice is indeed at the point of "dead load" contraflexure, then it is located at the position of highest shear and zero moment, under ideal conditions (therefore zero flange tension/compression). Since all shear is resisted by the web splice plates, which remain undamaged, then removal of the top flange splice plate should be able to be safely replaced if live load (traffic) is kept off the structure during the time the splice is actually being swapped out.

The relative positions of the stringer flange should not shift, especially if the remainder of the member is compositely connected to the slab with shear studs. If it is non-composite, then a fastening sequence can be easily devised to ensure that at least one or two bolt shanks remain on either side of the splice as the plate is being swapped out. The method to achieve this is to turn two bolts upside down at both ends of the top plate before taking out the reamining bolts. Remove all other bolts leaving the bolts shanks at the ends of the splice pointing up. The damaged flange plate may then be easily removed and replaced with a new flange plate and HS bolts.

Good luck.