Overplating/Repairing a Historing I-Beam 2

[Aytacoglu]

Hi All,

I am currently working to provide an overplating for an I-section that is a historic section of 4"x3" RSJ.

As you know, the historic sections have curvature between the web and the flanges (around 95 degrees). See the screenshot below for details.

The beam that I am dealing with has isolated holes to its web, hence I am proposing to overplate with angle section to cover these holes and to provide additional strength as requested by the client.

My question is that, since the top flange is coming at an angle and it is not straight, how is it practical to propose this repair detail? Is it the case that providing a packer plate to make this happen the right approach? Or even if the beam is slightly angled at the flanges, the contractor would be able to fix the angle plate to the top flange without issues?

I have provided screenshots below for information. It would be great if someone can help on this.

 

[Aytacoglu]

Forgot to include the shim plate on the web so that the angles will be fixed tightly. But you get the idea.

 

[ChorasDen]

I don't do any steel design, so I can't contribute to your question here, but I'm subbing to see if there are any follow-up's from those more knowledgeable.

 

[dik]

Can you attach a W4x4 to the bottom flange? Can you take any test coupons to see if the material is weldable?

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

-Dik

 

[GeorgeTheCivilEngineer]

I'd go for an unequal angle (don't know the US name but one leg is longer than the other) to ensure you are past any corrosion and into good web material.

 

[jayrod12]

Is removal and replacement an option? Even if they have to figure out some form of impressive temporary shoring for whatever is on top?

I only ask because whenever I've tried getting that intense with adding material, it often ends up costing less to just replace it. You'll end up chasing corrosion, it's like a mouse infestation, you can only see half of the damage.

 

[jerseyshore]

Are you reinforcing for corrosion or adding new weight (or both)?

I would think adding new steel as jayrod mentioned is going to be a lot easier unless you absolutely have no additional space to fit it in.

I also agree with dik that getting it tested is probably a good idea.

 

[bridgebuster]

I found a beam that was close in a 1909 Carnegie Steel Manual. I would use an unequal angle with the long leg down; better chance of hitting sound material. extend the angles beyond the damaged area then bolt to the top flange. You might be able to get away with just using beveled washers.

 

[ifitsmoving]

My understanding is that 4x3" RSJ are British sections originally - we used to use them here in Australia. If the top flange is not affected, why not just weld an overplate on the web? This has significant advantages:

[ul]
[li]When overplating esp. for strength you always need to think about how are you going to develop force into your overplate. The quickest way to develop the force is welding. If there is significant load in the member, bolt spacing may result in a need to extend that overplate a fair amount past the corrosion to get enough bolts in. Welding will allow much shorter development lengths. That said, for lightly loaded floor trimmers (which a 4x3" RSJ is likely to be), webs are often lightly loaded and corrosion like this may not actually be much of an issue and all you may need to do is cover the hole up to prevent it getting worse.[/li]
[li]Bolted connections can also be an issue due to bolt hole tolerances - if you use snug tight bolts, they will slip before developing their force, and over short lengths of overplate the amount of slip can be much higher than the level of deformation at which your original beam fails. Fitted holes may be required, or else fancy calculations of relative amounts of deformation due to bending vs. bolt hole tolerances could be required.[/li]
[li]Your bolted connection with packers is likely going to be a corrosion issue in long term service. You're adding 4x crevices with each angle. These will attract and trap moisture. You're also adding lots of sharp edges with your bolts, which will affect paint quality and reduce durability.[/li]
[li]No worrying about the flange taper. If you need to strengthen the flanges as well, weld a plate on the top of the flange (where you have access) or weld extra plates directly onto the flange taper.[/li]
[/ul]

The only reason I'd bolt on strengthening for such a small area is if the client really, really, really, doesn't want to weld, or the area is an explosion / fire risk. If you're dead set on bolting using your arrangement, then I'd suggest:

[ul]
[li]Check your shear and shear flow calculations. Does the existing web still have enough capacity even after the corrosion - can you just cover the hole without worrying about shear & shear flow? If not, Can you develop enough force horizontally and vertically to make your angles effective, both horizontally and vertically, and consider if bolt hole slop is going to be an issue.[/li]
[li]Get rid of the vertical shim plates on the web. They aren't needed because the angles will bear nicely on the flat of the web, and even if they don't, your packers are going to be almost as stiff as the angles anyway so won't help you match the profile. All they do is add an extra crevice to attract water and contaminants that will need sealing and painting. If the profile of the web is rough, then grind it smooth, or just accept it and seal the interface with flexible sealant (which would be a good idea anyway).[/li]
[/ul]

 

[dik]

Depending on the steel, you may not be able to weld. I was tasked with reinforcing a crane yard for a railroad a couple of years back due to corrosion deterioration. First thing I did was get coupons tested... high sulphur... hot short, not weldable... forms irons sulphides in the grain boundaries... The project was 'scrapped'. I don't know whatever happened to it.

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

-Dik