Filler for structural bolt holes

[TpaRAF]

We are working on a bridge repair project, replacing rivets in deteriorated structural steel with high-strength bolts.

In some locations, the hole is several times the replacement bolt diametre. The concern when the bolts are torqued to provide a slip-critical connection, the scab plates (over the holes) will deform.

There does not seem to be any epoxy products specifically made for this application. The bolt force is about 40 kips (160kN), so a very high compressive strength is needed.

Any ideas on what processes or materials could be used to fill the annulus around the bolts?

Thanks in advance for your help! RAF

 

[civilperson]

Weld the holes full and then drill/punch out the diameter plus tolerance. Goes pretty fast even with cosmetic grinding.

 

[TpaRAF]

Hi, CivilPerson:
Thanks for your input, but no joy on doing this. These are main girders on a bridge. Florida prohibits field welding; HAZ is an issue; punching not practical in-situ. RAF

 

[eromlignod]

How about steel bushings?

Don
Kansas City

 

[hydtools]

Can you use larger bolts?

Ted

 

[TpaRAF]

Thanks for the suggestions, eromliGnoD & Hydtools.

The condition is a thin flange plate with irregular corrosion around the original rivet hole. The repair consists of grinding the hole back to clean, sound metal then adding scab plates to restore section.

The proposed bolts are ~3/4" diametre, in a 2" or larger hole. When the bolts are torqued down to provide a slip resistance (structural) connection, the scab plates will deform.

So... the thought was to fill this void with something (perhaps epoxy) that can a) withstand the compressive force of 40kips and b) not fail under the shear stress when the bolt is engaged laterally.

If the welding could be used without creating a HAZ, that would be ideal. Since this is a large bridge girder, it's staying in place (no shop work, preheat, etc). Drilling is difficult but possible.

Thanks for pondering this problem! RAF

 

[CoryPad]

Why not use a steel insert (custom made on a lathe if small quantity) that is adhesively bonded to the plate with epoxy? That way, you have a rigid metal taking the high compression force, and you can have a small amount of adhesive, which is how they work best.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[minerk]

Machine inserts in shop with desired ID and OD sufficient to allow removal of corroded metal. Use a magnetic base drill to drill & ream holes in girder to allow press fit of inserts. Freeze inserts in liquid nitrogen and install.

 

[handleman]

Use thicker scab plates that won't deform. Granted, material cost would increase. However, the labor required to drill out corroded material, custom machine inserts, freeze them, and install seems as though it might cost even more. If solid scab plates are too much, how about 3" OD or larger 1" thick washers under each bolt head?

Any filler material that doesn't become a structural part of the existing beam is going to be unacceptable. The scab plates need to put force on the girders to generate friction and make the joint. If you put some filler in there to prevent deformation, the filler will be taking the pressure, friction, etc. and not the girders, and the joint will only be as strong as whatever connection you have between the filler and the girder.

 

[Tmoose]

Is the large hole through both pieces being riveted/bolted/clamped?

Regardless, If the insert's length is preventing the scab plate from deforming then the insert is probably also getting pretty much all the bolt clamping, and some memebers in the joint will be virtually "free" to slide within the limits of the insert-to-hole clearance.

Generally speaking A washer with thickness at least 2X the clearance will be not deform much. If the "bolts are ~3/4" diametre, in a 2" or larger hole" then I picture the radial clearance can be over 1 inch in some directions. Are the bolted flanges 2 inches thick?

 

[bvanhiel]

I think the solution is thick scab plates. You want the clamp load to go into the metal around the holes, not to be bridged by a spacer.

-b

 

[swearingen]

Scab plates, per AISC, would not be the answer. Remember that a slip-critical connection is designed for SERVICE loads. If it goes over service loads, it is also designed for full bearing so that when it slips, it bears on the bolts. If these holes are that big, and you're not willing to weld to make them smaller, you'll need to put in very large bolts to fill up the holes. Anything else would not be classified as slip critical.

Also, I agree with handleman, "Any filler material that doesn't become a structural part of the existing beam is going to be unacceptable."



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 

[plasgears]

Consider the use of a split tube to fill the space. Torquing down the bolt will expand the tube to fill the hole. The split is a shallow diagonal cut extending from below one face to just below the opposite face. It will be like two wedges. Analyse how much initial axial interference is needed to largely fill the hole.

 

[TpaRAF]

Thanks to all for the comments and input.

One aspect I must not have made clear is these holes (from corrosion of the beam flanges) are VERY irregular in shape -- more of an ink splat than a uniform, bushing-ready hole.

Regards, RAF

 

[swearingen]

For it to be a structural bolted connection classified as slip critical, it must be able to take factored loads in bearing. I do not believe you will be able to achieve bearing in your situation. I think the cost of the repair will be FAR more than anyone there realizes...



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 

[minerk]

How about longer scab plates with additional holes beyond the existing holes? The existing holes would still provide clamping force, and the new locations would prevent any movement between the members.

 

[prost]

Just thinking out loud...

Is this common practice in bridge building or maintenance to put bolts in holes that are twice the diameter of the bolts? That would seem like a dangerous design, given the many additional failure modes introduced with the remediation methods mentioned here; for instance, over many years, epoxies can break down, rendering the joint useless. With steel inserts, which IMO would be a marked improvement in structural integrity over epoxies, you might see them corrode enough so that the inserts are useless for load transfer.

 

[vesselfab]

prost, I read it as......the holes in main structural members behind connection plates had gotten to twice the size due to deteriation of the steel....ie...rusted like heck and now trying a to find away to fix. I really don't have an answer and quite frankly, i was really suprised at the way the original poster was going about trying to fix it. JBWELD (redneck epoxy here in the south) does not a satisfactory repair make.

I guess this is why we have bridges falling down around the country.

 

[TpaRAF]

Thanks for the suggestions from everyone.

"Minerk" is correct that the scab plates extend well beyond the damaged sections, to where solid connections are made (normal practice for this type of repair).

"Prost" summarizes the key issue - the voids are too large for any fasteners. Given the irregular shape, inserts do not seem feasible (even if we shape the voids). Corrosion will continue (exposed to salt water misting), so a non-metallic filler seems suitable here.

Bridges are deteriorating due to inceasing truck loads, increasing traffic and the lack of funds to repair them. That's why the US has had a rigorous inspection program in place since the 1970's.

Too bad there isn't enough money to fix all the problems. Usually, the bigger items are taken care of, and a confluence of smaller problems leads to those making news.

 

[ccw]

"Florida prohibits field welding" as a HAZ issue. ? ? ?

What is the problem? Weld splatter falls on an alligator in the swamp? Florida should review her "field welding" prohibition. Sooner or later this prohibition is going to cost a fortune, in otherwise unnecessary repair efforts. Bolting on scab plates, particularly for flange-to-flange continuum, has its limits.