Repair options for damaged steel column

[JADEN98]

I have been asked to prepare a report on repair options for a wide flange column (W6*15) damaged from collision in a mine. Although the damaged area (bottom 20" from the base plate) is far away from the critical zone of buckling, I believe repair is necessary considering the increased vulnerability of the section to local buckling and corrosion. The senior engineer at our office dismissed the case as a "non-issue" and said to "just put a plate on the damaged flange and suggest concrete bollard as an alternative long-term solution". Wouldn't it be necessary to heat straighten the flange before welding a cover plate on it? And if not, would the length of the plate above the damaged zone be equal to the weld length required based on the shear flow demand plus the width of the flange?
As for the alternative solution, wouldn't concrete encasing be a more technical solution rather than putting several bollards around the column? Should the reinforcement and anchorage of any concrete solution be calculated based on a composite section behaviour or just an independent protective cover against collision?

 

[human909]

I'd suggest you'd colleague is pretty correct. Though assessment of the corrosion issue both long term and immediate isn't possible from your description and the photographs.

My assessment from gut feel:
The current impact damage has not reduced the overall column capacity. Thus a repair isn't need to restore the column capacity. However given that you have been asked to write a repair report I'd recommend the repair to ensure that the client and everybody else can feel happy and safe. The repair your colleague has suggested would suit.

I'd suggest impact protection if there is heavy machinery around. Though if it is required for one then it is probably required for all. I don't know the weight of the machinery involved but I'd probably go with four metal bollards bolted into the slab. Impact protect is about providing a buffer space and an ability to absorb energy rather.

Corrosion could be a big issue if the product surrounding it is an accelerant. But there is insufficient information about the extent and the timeframe to make a judgement.

 

[JADEN98]

Thank you for your prompt response. I agree that the column situation is not critical yet but the report is necessary nevertheless . The metal bollard is a great suggestion. However, I wonder if heath straightening is necessary before welding the cover plate to the flange? And if so, what would be the criteria for determining the length of the cover plate above the damaged area?

 

[human909]

And if so, what would be the criteria for determining the length of the cover plate above the damaged area?

I'd have two criteria, in order of importance:
1. Big enough that it looks to the client to be a robust repair and a satisfactory conclusion to the issue raised.
2. Might as well be thick enough and long enough to provide equal replacement capacity to the entire damage flange. So maybe 1.5 times the length of the damaged area.


The time taken to; write the emails, escalate the problem, engage a third party, get a report written and to review the report, far exceeds the cost of the repair.

 

[phamENG]

From the OP:

I believe repair is necessary considering the increased vulnerability of the section to local buckling and corrosion.

From your second post:

I agree that the column situation is not critical yet but the report is necessary nevertheless

Which is it? Have you determined that the column capacity has been quantifiabley reduced below what is required? In what way is the column now more susceptible to corrosion? Did it have a coating that is now damaged?

I agree with human909 that this probably doesn't pose a structural concern. Based on the apparent scale those are, what, W6's? And light ones at that. Can't be carrying much load. So if there's not a structural concern with the column and it's only a question of a damaged coating, why not just repair the coating?

 

[JADEN98]

Well, The column has certainly lost a percentage of its capacity, not to the point of failure but enough that its overall factor of safety has decreased. The paint and coating are very weak against direct impact which means the damaged section does not have the same protection against corrosion as the rest of the column. So, the situation is not critical but not OK either. As human909 mentioned, the client's perception of safety plays an important role in these repair reports. Still, I wonder if heat straightening of the flange prior to welding of the cover plate is necessary.

 

[human909]

Well, The column has certainly lost a percentage of its capacity, not to the point of failure but enough that its overall factor of safety has decreased.

To me that isn't certain.

If the criteria of applicable load cases are the normal gambit then the member is likely still very much governed by the overall buckling rather than local failure. So by the normal criteria I would likely conclude there is no capacity loss and no decrease in factor of safety. Regarding corrosion it isn't clear either, there is insufficient information provided.

If the we are considering impact criteria as critical then yes we've lose capacity. But the best solution there isn't to engineer the column back to it's initial strength it would be to provide impact protection and likely provide it for all columns.

Still, I wonder if heat straightening of the flange prior to welding of the cover plate is necessary.

To what end? That solution is challenging and providing a suitable flange cover that restores capacity would be cheaper and simpler.

 

[le99]

I agree with your senior engineer on his claim that the repair is a simple matter - cutting and replacing the damaged portion to restore it to the original shape, however, I won't claim this is a "non-issue", which might get your company into the "liability trap". Tell the owner that while the damage does not have an immediate impact on its performance, but may have concerns if left alone. Then the owner will be more willing to spend time and money to fix it.

Bollard or concrete encasement? It depends on the limits of the activities around the environment. You should list the pros and cons of each, then discuss them with your senior engineer, or the owner.

 

[LittleInch]

Is this column actually taking any load at the moment?

If not why not just clean up this damaged area, flame cut or grind it out and weld in a replacement section??

You could even grind off the weld and make it look flat.

Then everyone's happy.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

If the concave dented area is out of the way, I'd simply weld a new BAR 3/8x6 over it with 1/4" welds... and leave the bent metal where it is, if it's not in the way...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Brad805]

These type of requests can start from a safety inspection, irritated worker or other factors. No amount of reports will stop it from being brought up time and time again in the future. Here we have a tiny column, so unless there is problem with access for a mobile welding truck or site safety protocols that prevent hot work, this seems like a case where reinforcing is simple. It will take longer for the welder to get to site and setup than complete the repair. You can bend it back and fish plate, or replace a region easily if there is no load. I would talk to your client.