Repair of Corroded Steel I-beam 4

[BMart006]

What are the common methods for repairing corroded steel sections? In this case I am looking at an A36 built up I-beam section where there is an approximately 1/8" loss on the lower part of the web on one side and a 1/8" gross loss with some areas penetrating 3/16" and 1/4" on the upper face of one half of the lower flange. The section has enough material to remain in service for the time being, but I'd like to know what are common methods for a future repair. Thanks!

 

[Guastavino]

Can you put an additional bottom plate on the bottom flange and weld intermittently? That should help with the bottom flange. As for the web, more difficult, but maybe not even needed if you get the flange straight. The flanges are doing the bending stress work. Not sure how to calculate how much web you would "need". Maybe some doubler plates?

 

[bridgebuster]

It involves bolting or welding angles, plates, etc. Steel repairs are somewhat custom tailored for the situation. Take a look at the attached (scroll towards the end to find steel details), it'll give you some ideas.

 

[UofAGrad]

Can you better explain how the member is built-up?

Assuming the added steel doesn't interfere, the web you can "Fish Plate" with original web thickness the depth of the beam on both sides of the corroded section. The flange would be a similar repair by welding a plate the same flange thickness on the outside of the flange, a depth D beyond the corroded section.

As NJL stated the web repair may not be needed but you can expect the corrosion to continue, this will put you ahead of the game.

 

[SlideRuleEra]

How much steel remains is more important than how much has been lost. If, say, the web is now "paper thin" the repair will be different than if half the the web thickness remains. As bridgebuster stated, repairs have to be customized.

http://www.SlideRuleEra.net

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[JedClampett]

One thing I like to do for all beam and column repairs is to shore the members (basically remove the loads) before the repair. It's expensive and a little risky, but I think it assures that the new repairs take all the loads.
If you have a column and the web is gone, that means that the flanges are taking more of the load. If you just repair the web, you're not removing the stress from the flanges. Additional loads might cause local problems.
One other issue to think about. Be careful welding to loaded existing members. The heat of welding reduces the strength and stiffness of the existing steel.

 

[bridgebuster]

@BMart006 - can you post a sketch or photos because I probably have something more specific than the generalized details I posted.

Going a little off topic, Wednesday I got sucked into redesigning and detailing about three dozen steel repairs -they're repairs at the ends of bridge stringers - because the contractor says they're unbuildable as shown (he's reasonably correct). The end diaphragms are skewed; whoever detailed them didn't realize a number of things like the proposed angle stiffeners hit the diaphragm flanges and bolting clearances exist for a reason.

 

[BMart006]

The beam is a tapered web beam. Due to security I cannot post a photo, but I've drafted a generalized section of the beam. The beam is not missing this much, but I've assumed rectangular sections to be missing at the deepest pitting depths for simplicity and conservatism.

 

[TehMightyEngineer]

Assuming it's not the entire length of the beam, I'd say you've got a fairly easy repair as the flange appears relatively unaffected. I'd needle gun the corroded area to solid metal, grind the surface to bright metal, prime areas not to be welded, weld an angle onto the web and flange tip, paint and go. You'll want to unload the beam as much as you can during this as the weld heat will take a bit of your beam capacity during the welding. For this reason (and possibly fatigue reasons) don't weld across the flange (perpendicular to the long axis of the beam). Extend the angle beyond the affected areas to "develop" the reinforcement. Seal it up good to prevent moisture from getting under the repair angle, repaint the entire beam, and call it a day.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

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[SlideRuleEra]

I would follow TME's approach to cleaning and prep, but go with filler welded into the web recess then a pair of web plates. As stated, the flange damage appears minor, and it is on the "large" side of the asymmetrical flange. Other than clean & paint, I would leave the flange alone. Using only web plates has the advantage of minimal changes to the beam's structural properties. Taper the ends of the web plates to keep from having a sudden change in section modulus.

http://www.SlideRuleEra.net

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[TehMightyEngineer]

I like SRE's approach. Mine is cheaper but his is more effective. Probably depends on what the beam is used for and how time sensitive/cost sensitive the job is. About the only thing I would caution with SRE's option is his welds at the web/flange joint may cause an unacceptable loss in capacity of the steel beam. Without knowing more it's hard to say whether that's an issue or not.

My thought for using the angle goes back to my paper mill background. Most heavily corroded steel beam were due to chemical, water, or steam leaks onto the steel at specific areas. Armoring these areas with as much metal as possible was often worth it in the event the leak source wasn't easily removed.

The other thing is make sure you stress the timely application of this repair along with proactive repainting and inspecting of other areas where corrosion may exist. That amount of corrosion does not happen overnight and I usually found it was due to lax facility maintenance of uncommonly inspected areas and equipment. For example, we had one corrosion repair job where they put our engineered shoring system in for the repair but then delayed the job for 6 months at which time the corroded beam actually failed and the equipment was left hanging off of piping. This made the job 10x more expensive and involved new columns, new framework for more shoring, etc.; to say nothing of the cost had the equipment ripped out the piping, likely shutting down that side of the mill and requiring replacement of the equipment. In short, impress upon them that waiting to the last minute to perform maintenance will cost them much more down the road.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Bret992]

Great stuff here everyone. I've been looking at bridgebuster's repair details and notes. Does anyone know of any design guides or references describing steel repair criteria such as percent section loss limits? I see 1/8" or 25% section loss (average) in bridgebuster's notes, but I've also seen people use 10% and I am just curious if there are different industry standards?

 

[bridgebuster]

@Bret992 - I'm not aware of any standard industry practice; it's subjective. The details I posted are from the NYC Transit authority, which, like all railroads, tends to be very conservative. Typically, on a highway bridge project if the load rating is adequate we might not bother fixing something-perhaps a paint job will suffice - or we might make a repair to avoid questions in the future. As a boss told memany years ago never leave an open bolt hole because invariably someone will think there's something wrong.

 

[BridgeSmith]

Looks like some good repair strategies have already been given. I would only add one caution - some welds may reduce the allowable fatigue stress range for the beam. If the beam is subjected to a high number of moderate to heavy loading cycles, you may have to use a different kind of weld or use bolted connections.

 

[SoFloJoe]

I did a fix like this a few years ago. Also consider the cause of the corrosion in the first place. We reinforced the Ibeam with 2 c-channels on either side (looks like you got this part covered) and as protection against future corrosion we encased the beams in concrete for the 1st 20" and applied a protective water proofing sealant on the concrete.