How to remove and replace a rusted steel?

[MisterBoy]

I have a conservatory which was formerly a hot-house. It has a concrete floor supported by some I-beams over a kind of cellar underneath and one of the uprights is totally shot - rusted right through big enough for your hand to pass through.

I'd love to simply drop the floor and replace it but I'm more concerned it needs fixing right now and funds mean a like-for-like is probably all I can do.

It is bolted to some sort of plate on the floor, and to another steel at the top and all the bolts are pretty rusted too. What would be the typical way to get this out so a new one can be bolted in place? Is it simply a case of hiring a heavy-duty grinder?

 

[mattylad]

Im no expert but Id have thought you also need to hire acro props to support the flooring above too.
Consider - how will you get a replacement in? physically and with what manpower?

Can you provide photos of the hole (close-ish) and the whole beam so the experienced folks can assess the issue for you.

 

[MisterBoy]

It's already got one acro as we don't trust it to be strong enough so yeah we'd probably need more to support each side.
It's only about a 5 foot length, I'd need to double check but it looks like it's close to a 150x150x30 so quite manageable to get through a doorway. Not like the 6.5m one we had done on another project without crane access.

I can grab a picture but the part which got me thinking was how to deal with totally seized bolts - I've already had a SE confirm it should be replaced.

 

[MisterBoy]

So this is the problem area It turns out water was coming through the wall (it's underground) and literally running over it.

Here's the top. Actually, those bolts don't look too bad so maybe this isn't a problem - I remembered them being far worse.

And a couple just showing the structure generally. Strikes me as a right mess, I wish there wasn't a pillar in the middle!

 

[Tigercubrider]

Many people might just buy a second acroprop and leave the old beam in place.

Have you looked into adding more beams, spreading the load, and going side to side w/o pillars?

 

[MisterBoy]

Many people might just buy a second acroprop and leave the old beam in place.

Have you looked into adding more beams, spreading the load, and going side to side w/o pillars?

I mean it has been there for about 2 years now

I don't really get why it was done this way at all - why they have pillars at the sides instead of going into the wall for instance. Why they didn't use full-width steels, it's only 3-4m. There's a very slight pitch to it - left and right - and the concrete looks like they might have used a tin roof and poured a slab on top. I don't even know if that middle pillar is needed, doubt an engineer was ever near it
With the ceiling only about 6 foot, it's a pain. I would ultimately like to turn it into a usable space.

 

[domdee]

Pictures don't seem to be working for me on PC or phone.

If it was me I'd prop it well in the area.

Cut the beam into 3 with an angle grinder.

Remove the middle.

Cut the nuts/bolts with the grinder at the top and bottom

Add new steel. Might be hard to use existing holes so maybe new ones will have to be drilled.

A 5ft length isn't going to break the bank so will be a cheap enough fix.

Make sure you paint the beam well before installation with some rust prevention. Red oxide or zinc based primer?

If you want to make it more usable, maybe you could excavate the down. Obviously some kind of design/building regs/structural calcs will be required but if you was to do it on the quiet you could dig down a few feet round the perimeter, pour a footing/foundation, then dig out the middle to required depth to lay a new insulated slab. Moisture/water will be an issue to some sort of tanking will no doubt be required. And dpm required for slab/foundations.

 

[MisterBoy]

@domdee sorry my mistake with image copying.

Yeah I have wondered about digging down. We had a S.E. out a while ago to advise on the structure generally and he pointed out this can add more 'leverage' outside the wall as it has a greater height of soil pushing in but nothing is impossible. I think that might be the plan one day, but we'd probably drop this entire floor/ceiling at the same time as a concrete slab is not exactly ideal.