Filler for structural bolt holes
Filler for structural bolt holes
(OP)
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
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





RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
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
RE: Filler for structural bolt holes
Don
Kansas City
RE: Filler for structural bolt holes
Ted
RE: Filler for structural bolt holes
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
RE: Filler for structural bolt holes
Regards,
Cory
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RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
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.
RE: Filler for structural bolt holes
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?
RE: Filler for structural bolt holes
-b
RE: Filler for structural bolt holes
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
RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
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
RE: Filler for structural bolt holes
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
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.
RE: Filler for structural bolt holes
I guess this is why we have bridges falling down around the country.
RE: Filler for structural bolt holes
"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.
RE: Filler for structural bolt holes
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.
RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
now there is much legal / political / engineering turmoil (not to mention the deaths!).
i have no idea what the cause of the failure was.
regards
magicme
------------------------------------
there's no place like gnome.
RE: Filler for structural bolt holes
RE: Filler for structural bolt holes
According to History Channel "Engineered Disasters" the epoxy had a "creep" failure in shear. At one time, after the failure, there were about 16 companies sueing one another over who was at ultimate fault for the failure. There is a great long thread on the "Big Dig" panel anchor failure over on "structural engineering". That is probably where this thread belongs also.
RE: Filler for structural bolt holes
http://ww
According to this field welding is discouraged, but NOT prohibited. This is clearly a case where field welding is necessary. Some work will need to be done to determine metallurgy and developing the best weld procedure, but it is definitely the best course of action.
RE: Filler for structural bolt holes
Minerk -- This particular jurisdiction of the DOT has had bad experience with field welding, and will generally reject repair plans calling for it. The real issue is having the government low bidder using the lowest paid welders he can get. Some of this work is overhead, the hardest welds to make. Weld certs only go so far.
Majicme, ccw -- One thing being considered in the Big Dig forensics is improper installation of the epoxy in an ... overhead use. Regardless of the quality of the method or material, it usually comes back to how well it can be installed or fabricated in the field
RE: Filler for structural bolt holes