Floor strength for heavy(ish) machinery

[NickM]

This came up on the thread about the Baileigh table saw review - I thought I'd start a new thread to avoid that one drifting.

That saw weighs around 200kg and in asking how feasible it would be to get it up some stairs to a room above my garage, I was prompted to think about whether the floor will be strong enough.

The set up is as follows:

- Floor joists are 3" x 8" and are spaced at 15" on centres. The span is around 16.5'.
- The floor is 20mm chip board.
- The building is brick construction and the roof is a pitched roof.
- Although the saw wouldn't be right in the middle of the span, I can't get it very close to the wall because of the pitched roof.

The joists seem large, strong and relatively closely spaced to me (but I'll freely admit that I'm guessing...), but I wondered about the chipboard. I could put the saw on another sheet, making sure that it straddles a couple of joists which I think would make it stronger. I might need to be careful if I decided to put the saw on a mobile base because of the extra pressure going through the wheels.

Any thoughts?

Thanks.

 

[MikeG.]

Those joists are sized for a uniformly distributed load. They are barely strong enough for that. Whilst 200 kg isn't huge, it is a point-load, and as such I absolutely would not put that weight on that floor (even if you could get it up the stairs), unless the floor was radically reinforced.

 

[RobinBHM]

Im wondering if you sistered 3 or 4 joists where the saw will sit, would be ok.

Say with 10 x 2 joists -they dont have to be full length, a foot or so short of each end would work.

If you have some bags of sand or cement around, lay 8 at the spot where the saw will sit and measure the sag.

Note: I agree with Mikes advice, just trying to come with some solutions / ideas, we dont people being stopped from buying new toys

 

[NickM]

Thanks. Very helpful.

 

[MikeG.]

I'm afraid I think you need some steel in underneath that floor to cope with that sort of point-load. Further, that won't be all that happens up there. You'll bring other tools, equipment, timber etc up in association with the table saw. You'll stand adjacent to the saw yourself. Unless you can get a prop under the floor, I honestly think that steel is your only answer (or a glulam beam, perhaps...just that steel tends to be cheaper).

 

[MikeG.]

Im wondering if you sistered 3 or 4 joists where the saw will sit, would be ok. Say with 10 x 2 joists -they dont have to be full length, a foot or so short of each end would work...........

Every structural engineer in the country who sees this is cringing right now! Seriously, please don't anyone try this at home.

 

[Peterm1000]

Ok - about to show my stupidity. So why is it OK to have 2 people totalling 200kg in a double bed weighing a further 100kg all going through 4 posts, but not OK to have a lighter saw on the same floor? We have even had 4 full sized blokes stand next to each other in one of our upstairs bedrooms and the floor has not collapsed.

 

[MikeG.]

A floor isn't judged to be strong enough simply because it doesn't collapse, BTW.

That bed isn't even OK on that floor. The maximum span of a 200x75 joist is 4.83m at 400 C's, with the minimum possible dead load on top. The span is a foot longer than that. So in the absolute ideal circumstance, with the minimum dead load and an assumed domestic UDL on top, that floor doesn't work...........never mind sticking a point load on one or two joists right in the middle.

Besides, those 4 bed posts are each putting down a point load of 300/4 = 75 kg, probably spaced some 1500mm apart and thus putting the load onto multiple joists. The table saw is concentrating its load on one or two joists, and of course it would have an operator standing there too.

 

[RobinBHM]

Im wondering if you sistered 3 or 4 joists where the saw will sit, would be ok. Say with 10 x 2 joists -they dont have to be full length, a foot or so short of each end would work...........

Every structural engineer in the country who sees this is cringing right now! Seriously, please don't anyone try this at home.

I cant actually what is wrong with what Im proposing. We are only talking 200kg. Over 2 joists thats an increase in load of 50kg at each end.

If existing joists are sistered, that would increase the stiffness of those joists. The bending moment near the ends of a beam are very small, so the sistering isnt required the whole length. The only risk is increasing the load on the joist support, but thats only 50kg per joist end -if they are on hangers there would be a big safety margin.

I realise 10 x 2 might not be a big enough section -ive not looked at the span tables, but given the fairly small load and the joists are being effectively double in section, I wouldve thought it ok.

I did think of making a flitch beam of one of the joists, but thats exprensive and a lot of work. A few lengths of joist glued and bolted is easy.

 

[MikeG.]

.........I cant actually what is wrong with what Im proposing...........

I don't know how much clearer I can make it. That floor is too weak for normal domestic loads. It shouldn't be used as a floor at all. You are proposing to stick a weight in the middle of it, and that will take the deflection beyond acceptable limits. It really is that straightforward. Strengthen the floor from below, or forget the whole idea. It's that simple.

BTW...the hangers argument is irrelevant. The figure that this floor will fail on is deflection. It will bend too much.

-

ETA............oh, whoops..........you were arguing about a short sistering arrangement. Sorry. Then you've got to demonstrate that your fixings can take the strain you are proposing, given that they are the only thing taking the deflection. Span tables aren't going to help you, because they work on a simply supported beam principle, and yours has no end support.

 

[NickM]

.........I cant actually what is wrong with what Im proposing...........

I don't know how much clearer I can make it. That floor is too weak for normal domestic loads. It shouldn't be used as a floor at all. You are proposing to stick a weight in the middle of it, and that will take the deflection beyond acceptable limits. It really is that straightforward. Strengthen the floor from below, or forget the whole idea. It's that simple.

BTW...the hangers argument is irrelevant. The figure that this floor will fail on is deflection. It will bend too much.

-

ETA............oh, whoops..........you were arguing about a short sistering arrangement. Sorry. Then you've got to demonstrate that your fixings can take the strain you are proposing, given that they are the only thing taking the deflection. Span tables aren't going to help you, because they work on a simply supported beam principle, and yours has no end support.

In fairness to Robin, it’s not his floor. It’s mine, so I suspect he has already forgotten about it!

Anyway, I appreciate the input. I need to have a think about what to do.

 

[Peterm1000]

A floor isn't judged to be strong enough simply because it doesn't collapse, BTW.

Thank you - I don't claim to be Einstein, but I had that bit figured out!

I think you saying that floor isn't strong enough to have anyone stand on it let alone put the equivalent of 2 people in the middle of it... I suspect there are multiple houses out there like that today that haven't had someone fall through the floor yet.

 

[Trevanion]

I know someone with a pretty similar setup with 10" x 3"s on 16" centres and 20mm chipboard on top on about 2 20ish ft spans between the walls and middle beams in the top of a sheep barn. I know that his his Wadkin DM morticer is in excess of 300kg, I think the Dominion Morticer that sits right next to it is over 400kg, then there's a 4 sided planer moulder in there which I think was about a tonne and a half, then there was a seriously heavy spindle moulder that was well over a tonne not too far away from it either. Plus a few other machines in the 100-200KG range. In all, there are several tonnes on these timbers and the deflection is almost nil.

Not sure if that helps you out at all but I'm sure Mike's maths make sense, it's not my field of expertise so I won't comment.

 

[NickM]

Thanks Trevanion

I’m certainly not planning to load it up that much! I couldn’t get that sort of machinery up there even if the floor was up to the job!

Anyway, the diet starts tomorrow (homer) ...

 

[MikeG.]

Nick, you are being very selective in who you listen to. You seem only to hear those people who say what you want to hear.

 

[sunnybob]

I have no technical advice to give, I dont know right from wrong, but I do have to mention a point that many people dont consider in situations like this.
Insurance claims when it all goes runny on you.

Assuming Mike is quoting building regulations, then anything less than his dimensions will render your insurance null and void when (IF) it falls through the floor. Property and people damage will come squarely back to the person who decided to ignore building regs. Insurance companies always have a good laugh when told that so and so did that and it worked for them.
Thats all. Its your house and your machinery.

 

[NickM]

No, I’m listening to everyone. Particular thanks for your considered and expert input. I’ll certainly be having a look to see what I can do in terms of reinforcement/re-thinking.

Thanks again.

 

[Peterm1000]

The maximum span of a 200x75 joist is 4.83m at 400 C's, with the minimum possible dead load on top. The span is a foot longer than that.

I was really surprised by that comment so I looked in the building regs (we just had a big extension built). That's what it is for C16 timber. For C24 timber, the maximum span is 5.12m so if it's built in C24, then the span should be fine. All our joists were C24 as there was basically no price difference.

They also say these are the spans before you get beyond the deemed acceptable 14mm deflection of the floor. I guess if that happens, you start to get cracks in the plaster below.

Based on all of this, it does seem a little unwise to have a load of heavy machinery upstairs (not least think of how hard it will be to get all that equipment up there). However, the idea of it all crashing through the ceiling feels a little dramatic.

If in doubt, I would speak to a builder or structural engineer.

 

[MikeG.]

.......... I looked in the building regs............

I don't want to split hairs, but there are no longer any span tables in the Approved Documents (BUilding Regs). And I have no idea what table you are looking at, as mine for C24 give a max span of 4.97 at 400 C's.

 

[Doug71]

There must be so many first floors underspeced.

I got a nice freestanding bath for my conversion, when I checked the specifications it was over 300kg when full of water, add a couple of people and you are talking 450kg+.
I made sure the joist would carry it but the builder and building control didn't pick up on it at all yet if I said said I was putting a cast iron table saw up there I'm sure there would have been an issue.