Remove and replace a primary corroded U-beam from a steel structure 1

[Mizu22]

Hi everyone,

I am new to this forum and I have just shifted my work from a design consultancy to a mining site.

I have a question regarding removing a fully corroded primary U-beam from a steel structure and reinstalling a like for like beam later. I understand that the load path needs to be understood first and temporary bracing/props need to be installed in place before removing the beam. However, I have no experience in the area of structural remedial works and never worked with temporary structures, so was hoping someone could help me understand the load capacity of temporary bracing, where and how should they be installed, what are some critical structural aspects to consider and maybe share a link or two of study material to understand steel structural remedial works. Would be very grateful for all the help and answers. Thanks.

 

[Enable]

You have the general gist of it but the particulars are heavily site dependent. It's rather impossible to say "do XYZ" when we don't know the structure or service considerations surrounding the repair. So what I will do is offer some general insights that may help:

1 - Don't just look at what load the beam was carrying, see where it went. If the structure is deteriorated enough to warrant replacement it is likely the load has been transferred somewhere else it wasn't originally intended to. Try and find the new path and decide if upgrades need to be done. Though, if this is a simply supported beam there may be no alternative load path and things are just working.

2 - Braces need to go wherever they need to go. Annoying answer, eh? But you need to evaluate the structure for the load conditions and place temp supports where required. This will include not just your vertical loading but your lateral loading as well (was the bream acting as a brace in some manner to a weak-axis of a column for instance). If you are dealing with an all steel structure braces would likely be field welded (unless you have hot works considerations for the mine). You'll want to pay attention to whatever you are welding so that you don't cause stress distortions / over-heat flanges unless you unload the entire structure. See Ricker, David (1988) Field Welding to Existing Structures, AISC.

3 - You are at a mine and if heavy equipment can get at your temp works in any way, make sure they are beefy and redundant. Even if you have the area cordoned off I would exercise a good amount of care given where you are. You also might have to think about impact loading if things can drop from above.

4 - Since you're dealing with structural steel the capacity of temp works would be calculated same as anything else. Given the particulars you may need scaffold or opt to use aluminum props; values can be found from the literature for these items. I'm a fan of multi-props by Peri and you can make nice towers out of them.

I don't know of any literature that deals specifically with this. But here are some that you might find helpful

Alberta Repair of Bridge Structural Steel Elements Manual
Structural Magazine - Shoring the Unshorable (Structural Steel Repair Case Study)

I rather like this book for a general overview of the temp works space.