Load bearing capacity of 2nd floor concrete slab?

taiwanluthiers · Mar 5, 2019

I just moved into a new shop in Taiwan. It’s a 3 story residential construction, old building but built out of reinforced concrete and brick facade. I’m on the second floor and the floor is 6 inch concrete slab with I think at least 1 inch steel rebar as reinforcement. The span is 2.5 meters and the support beams are basically 18 x 18 inch reinforced concrete beams that are really strong.

My question is assuming I can get the machines up there do you think it will support a 4000lb Bridgeport type mill? I can get 3 phase power brought in if necessary as the tenant on the first floor is a factory.

SteveF · Mar 5, 2019

Find out who built the building and ask them. Or if you happen to be in Taiwan, Texas the local Plans and Inspections office should be able to tell you what the minimum floor loadings are in the building codes. May even have a copy of the original building plans. If you are in Taiwan, Taiwan, I don't know if the same would apply.

Steve

EPAIII · Mar 5, 2019

Yes, your location says Texas and United States. I live in Beaumont, Texas but have never heard of Taiwan, Texas. Exactly where or what is that?

As for reinforced concrete buildings, they cover a lot of territory. I have seen ones that would be at home packed with M1 Abrams tanks bumper-to-bumper and others which would be a risk with a metal office desk if it wasn't in close proximity to one of the support columns. One company that I worked for in Miami built an addition on the back of their building. They called it office space so the architect designed OFFICE SPACE. Then they filled the second floor with floor-to-ceiling and wall-to-wall boxes of records; you know, those cardboard file boxes. Fortunately the architect saw that and quickly told them that they should remove them before it collapses. So, you can exceed the load bearing capacity of a reinforced concrete structure.

Yes, do check with your local building department. They should have plans on file. And if they do not, they can certainly send out an inspector who can advise you on this. Any competent architect should also be able to inspect it and advise you but they would probably charge more for the service.

Side note: That Miami company was a TV station and the first floor was occupied by the news department. So if it had collapsed, it would not have been a big loss; perhaps even a plus for the city.

PeteM · Mar 5, 2019

EPAIII said:
. . . Side note: That Miami company was a TV station and the first floor was occupied by the news department. So if it had collapsed, it would not have been a big loss; perhaps even a plus for the city.

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bryan_machine · Mar 5, 2019

@PeteM - you don't watch enough TV if you don't get the insult.... (And you are wise to not do so....)

implmex · Mar 6, 2019

Hi taiwanluthiers:
Just as a point of comparison; I'm also on the second floor of a concrete building.
My floor is 10" Dycore precast prestressed concrete with 2" of concrete topping.
The unsupported span is 25 feet and the total span is 50 feet.

An engineering assessment reveals that the live load capacity is 110,000 lb.
I have about 25,000 lb on my side and my co-tenant usually has about 15,000 lb in his space.

Your 4000 lb Bridgeport is likely not a problem, but I'd get the engineering report if I was at all unsure.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

taiwanluthiers · Mar 6, 2019

I live in Taiwan, it’s a country and not a town in Texas. I only recently moved there and hasn’t gotten around to updating that.

There’s been many major earthquakes in Taiwan and this building was built well before that so if it can weather that its fine I think.

Almost nobody builds out of wood here because domestic logging trade is basically illegal. There’s not enough land here to cut trees down and the few that remains are protected.

I want to start up a luthier shop but I want to put in a Bridgeport and a lathe as support (those machines would save me thousands of dollars of not having to order from Stewmac

EmGo · Mar 6, 2019

taiwanluthiers said:
... do you think it will support a 4000lb Bridgeport type mill?

A bridgeport-type mill is much closer to 3,000 lbs than 4. A waterbed weighs almost that much. And a little lathe for turning lute-type parts is going to weigh close to nothing. I wouldn't worry.

CountryBoy19 · Mar 6, 2019

EmanuelGoldstein said:
A bridgeport-type mill is much closer to 3,000 lbs than 4. A waterbed weighs almost that much. And a little lathe for turning lute-type parts is going to weigh close to nothing. I wouldn't worry.

Throw in tooling, fixturing, operator, 50 lbs of swarf collected around the base, and some stock leaned against the wall behind it and I say it never hurts to be conservative and figure 4k for purposes of floor loading calculation.

Illinoyance · Mar 6, 2019

You need to contact a local structural engineer.

Rudd · Mar 6, 2019

One more time - it is near impossible to reverse engineer a concrete structure and come up with a bearing capacity unless you have the original drawings. If you have those, it should list the floor loads - at least if designed here in the US.
The added fun is - even if you have the original drawings, was it built like that? There is no way to tell. Did the bars sink to the bottom of the pour because they weren't well supported? Concrete slabs see negative moment if poured continuous over a support - the steel needs to be at the top there.
Are all the bars even there?

DDoug · Mar 6, 2019

Rudd said:
One more time - it is near impossible to reverse engineer a concrete structure and come up with a bearing capacity unless you have the original drawings. If you have those, it should list the floor loads - at least if designed here in the US.
The added fun is - even if you have the original drawings, was it built like that? There is no way to tell. Did the bars sink to the bottom of the pour because they weren't well supported? Concrete slabs see negative moment if poured continuous over a support - the steel needs to be at the top there.
Are all the bars even there?

Was it "concrete" or "Bubble gum" ?

taiwanluthiers · Mar 6, 2019

If these concrete slabs weren't properly done the last big earthquakes would have revealed that in a very big way.

triumph406 · Mar 6, 2019

Rudd said:
Did the bars sink to the bottom of the pour because they weren't well supported? Concrete slabs see negative moment if poured continuous over a support - the steel needs to be at the top there.
Are all the bars even there?

If the bars are at the bottom of the pour they would be in tension, which is where I would want them in a slab, rather than at the top

rjs44032 · Mar 6, 2019

taiwanluthiers said:
I live in Taiwan, it’s a country and not a town in Texas. I only recently moved there and hasn’t gotten around to updating that.

There’s been many major earthquakes in Taiwan and this building was built well before that so if it can weather that its fine I think.

Almost nobody builds out of wood here because domestic logging trade is basically illegal. There’s not enough land here to cut trees down and the few that remains are protected.

I want to start up a luthier shop but I want to put in a Bridgeport and a lathe as support (those machines would save me thousands of dollars of not having to order from Stewmac

Hello taiwanluthiers,

Just curious. Over here luthiers make stringed instruments. If you can't buy wood there, how will you run a luthier shop? Do you have to import the hardwoods? I spent some time in my youth working for a luthier here in Ohio. Fascinating work. But I was drawn to working with metal. Good luck with your business.

Best Regards,
Bob

EPAIII · Mar 6, 2019

I worked in TV stations for most of my career. With some notable exceptions, I do not have much respect for the TV news crews. Most of them are only concerned with their own career and the only question that they ever ask themselves is, "How will it look on my resume?" This is NOT a political remark as I didn't often/ever know the political leanings of the people. It is just about their character in general and how they approached their jobs and the people they worked with.

PeteM said:
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EPAIII · Mar 6, 2019

I was thinking the same thing. Near the bottom, but an inch or two above it so they are completely encased in the concrete. Re bars in tension is the whole idea of reinforced concrete.

triumph406 said:
If the bars are at the bottom of the pour they would be in tension, which is where I would want them in a slab, rather than at the top

Chip Chester · Mar 6, 2019

In no particular order: Put your Bridgeport near a corner or a support pillar. Even if it's rated for the weight, keep in mind is's essentially a point load (at building scale) and 'within limits' may still result in some bounce. (Like sitting on a concrete bridge in heavy traffic.)

If the standard techniques for investigation don't yield results, try to find out what business have used that floor in the past, and what they had up there. May help with your decision making.

Yeah, news. But those boxes and boxes of records would probably fit on two hard drives when scanned. Wonder if they were actually videotapes...

taiwanluthiers · Mar 6, 2019

I doubt the records will tell much as in Taiwan laws are not followed to a T like the US is. However since 1999 building codes have tightened considerably because there was a bad earthquake that killed over 10,000. A lot of the buildings had trash stuffed inside support columns where concrete was supposed to be. The earthquake obviously collapsed all of those buildings and those that survive are most likely structurally sound.

In Taiwan earthquakes happen with such frequency that any improperly built buildings would not survive more than 20 years.

DDoug · Mar 7, 2019

Rudd said:
Concrete slabs see negative moment if poured continuous over a support - the steel needs to be at the top there.
Are all the bars even there?

triumph406 said:
If the bars are at the bottom of the pour they would be in tension, which is where I would want them in a slab, rather than at the top

EPAIII said:
I was thinking the same thing. Near the bottom, but an inch or two above it so they are completely encased in the concrete. Re bars in tension is the whole idea of reinforced concrete.

Specific example here. Not just any slab.

Load bearing capacity of 2nd floor concrete slab?

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