Corrosion of Steel Joists

[PaulBPE]

Looking for typical repairs made to steel bar joist, more specifically, I am trying to discern at what point the section losses observed require replacement vs. rehabilitation/repair.

Structure: Maintenance Bus Facility, 90' x 100' with 48" deep bar joist roof spanning CMU walls.

Problem: Areas of severe paint peeling with areas of 30%-50% section loss in the horizontal legs of bottom chord members, an isolated area with areas of 100% section loss in the horizontal legs of bottom chord members, broken tack welds along bottom chord due to accumulation of pack rust between vertical legs, and verticals and diagonals with 30%-50% section loss at isolated lower panel points. These joists are about 50 years old.

I usually offer repair recommendations for bridge structures so wanted to get some general opinions on what the standard practice is for these types of structures. Is it worth the time to perform welded plate repairs throughout 10-12 joists, or is it just as intensive to replace the roof considering all of the piping and conduits obstructing access for repairs? How critical are the tack welds for the bottom chords (are they considered in the design or is just to keep things rigid during fabrication)? Please check out the photos I have uploaded.

I look forward to seeing what everyone thinks.

 

[dik]

Initial appearance is not good... likely a 're-do' project; I don't think it's salvageable.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JedClampett]

But think of all the money they saved.
I'm sure that savings was invested and is being used for the repairs.

 

[bones206]

Here's a random collection of my thoughts:

- If temporary removal of utilities can be accomplished without out too much pain, retrofit joists may be feasible. Most likely this would be a two-piece joist with a bolted splice, installed next to the existing damaged joist to remain in place.

- Lead times on joists - especially two-piece retrofit joists - is extreme right now.

- If relocating the utilities is a nonstarter, repairing/reinforcing the existing joists is certainly feasible. The amount of acceptable section loss would depend on the stress in each member, but I personally would repair/replace anything with more than 20% section loss, regardless of the stress in the member.

- Ultimately it's a balance between a multitude of factors, but if the worst corrosion is limited to a 10-12 joists, I would lean towards repairing in place. If it was widespread throughout the roof and throughout the entire joist span, repair in place would then be infeasible.

- I had a project a few years ago adding some industrial curtains to a bus facility in NYC. My guess is this corrosion was caused by bus washing operations and not having curtains to protect the roof joists. If that's the root cause, they should address it as well. Those curtains have structural support requirements, so it would potentially make sense to incorporate those supports into the joist repair project.

 

[ThorenO2]

Never seen a chord lose a whole leg. The quality assurance required for extensive welded repairs on 10-12 48’ joists would seem very difficult to achieve. Too many different conditions with different variables to keep track of, too many obstructions to document — you’ll likely do better with replacing all the bad ones where you’ll be assured.