Floor Load Rating

[gafftaper]

My theater is 4 years old, since I wasn't here when it opened there is a lot of important information I don't know about the building. "Grease" is coming this spring and with it the discussion of if we can handle a real car on stage. I just found this diagram below. I'm wondering if we can assuming anything about the load rating based on the diagram without knowing any span information. I guess the only thing I can KNOW for sure is that there is 2x3 around the perimeter of the 4x8 plywood and base my load calculation on that. Can I assume that there is a 2x3 every 24" or is that too much?

 

[MNicolai]

Ever have a scissor lift out on your stage?

 

[gafftaper]

Ever have a scissor lift out on your stage?

Not that I know of, but I would like to know if I can.

 

[JD]

Still best to get an engineer to look at it and sign off. That way, the liability is set if something happens.

 

[MNicolai]

I was going to say, a scissor lift weighs about the same as a car. Find anyone who remembers a lift on the finished deck without problems and you've got your answer.

If your stage is slab-on-grade, it may suffice to find anyone with the same or similar floor construction. If there's a cavity for traps or rooms below your stage, you definitely want to first consult an engineer.

I'd try digging up the name of the architect or structural engineer from when the place was built and asking someone at either of those firms. 4yrs old is a young building. Good chance you can get on the phone with someone who worked on the project.

 

[DuckJordan]

Looks like the same style construction as our stage. We do have a pit with traps but did have a structural engineer come in anyway, Ours can handle a semi truck fully loaded. Throughout the floor (except right on the traps) however our pit can raise and lower an suv safely.

 

[venuetech]

can you access a floor framing plan from the construction drawings?

 

[Footer]

Drop the engine out of the car to start with... you bypass all the fire issue and really cut down on the weight. Sawzall the top off, bit of white duct tape for the interior... your all set.

Is there a basement or trap room below your stage?

Looking just at that drawing and assuming there is a slab on dirt below you should be just fine. Cars don't actually weight as much as you might think they do... and if you get that engine out they don't weight much at all. Your floor will be able to take the point load... the punch through on that deck will be obscenely high. It then all comes down to the loading of your floor. Your spreading a load out across roughly 75 sq ft on 4 points... that is 54# a foot for a 2 ton car. Well within most stages limits. Like others have said, get someone to give you the OK but you should be fine. Drop that engine though and drain ALL the fluids before it gets in the building.

 

[BillConnerFASTC]

Probably can assume stage was built to code, so at least 125 PSF. A parking garage deck is only required to be built to 40 PSF. So probably good. However a parking deck has a concentrated load requirement of 3000 pounds on an area 4.5 x 4.5 inches, and there is not a code required concentrated design load for stages. I have used 2000 which was the code requirement till I think 2005.

Cars today seem to range from low 2000s to mid 5000s for a big SUV or pickup, and a 57 Belaire - which I once had - was around 3200. A scissors lift ranges from 6000 to 11000, a loaed fork lift similar, except loaded the fork lift is mostly on two tires, not four. In any case the 125 is fine for all, since around a cars 6 x 18 feet that's 13500.

So the concern is the concentrated load. This can be easily calculated if you know spacing of sleepers. I use 24" for 1.125 ply - our standard - or 16" for 3/4". With 2x4s those are spans of 20.5" and 12.5". Keep in mind that two layers of 3/4" is roughly 75 to 80 percent as strong as one layer of 1.125.

Stopper blocks between the pads or lack thereof also would be a factor, and not shown in your detail.

So probably fine to drive a Caddy across your stage but sleeper spacing could be a factor to a failure and pads could suffer damage if loaded and no stopper blocks.

 

[lwinters630]

If there is concrete under the plywood then yes. I currently have two stages of similar construction and we drive scissor lifts on them all the time. However if you put it on casters they could mar the hardboard.

Also that floor construction is a floating floor, note the .37 waffle pad, similar to a gym basketball floor to give a bounce. And they drive lifts on gym floors.

 

[Robert]

Drop the engine out of the car to start with... you bypass all the fire issue and really cut down on the weight. Sawzall the top off, bit of white duct tape for the interior... your all set.

Is there a basement or trap room below your stage?

Looking just at that drawing and assuming there is a slab on dirt below you should be just fine. Cars don't actually weight as much as you might think they do... and if you get that engine out they don't weight much at all. Your floor will be able to take the point load... the punch through on that deck will be obscenely high. It then all comes down to the loading of your floor. Your spreading a load out across roughly 75 sq ft on 4 points... that is 54# a foot for a 2 ton car. Well within most stages limits. Like others have said, get someone to give you the OK but you should be fine. Drop that engine though and drain ALL the fluids before it gets in the building.

Footer is right on about the fire safety issue. You may have more trouble finding out how to get all the gas and flammable liquids out of the engine. While I suspect most never think about it on school stages, I commonly run into limits on the amount of gas or propane allowed in vehicles in performing arts centers or convention centers. They don't allow full tanks of gas, diesel, or propane. Yes I know that half empty tanks may have a greater explosion risk than a full one. I guess they are just trying to limit the fuel source.

 

[BillConnerFASTC]

Here is what NFPA says about vehicles, and while written specifically for exposition facilities - car shows - this has been applied to stages:

12.7.5.4 Vehicles. Vehicles on display within an exposition facility
shall comply with 12.7.5.4.1 through 12.7.5.4.5.
12.7.5.4.1 All fuel tank openings shall be locked and sealed
in an approved manner to prevent the escape of vapors; fuel
tanks shall not contain in excess of one-half their capacity or
contain in excess of 10 gal (38 L) of fuel, whichever is less.
12.7.5.4.2 At least one battery cable shall be removed from
the batteries used to start the vehicle engine, and the disconnected
battery cable shall then be taped.
12.7.5.4.3 Batteries used to power auxiliary equipment shall
be permitted to be kept in service.
12.7.5.4.4 Fueling or defueling of vehicles shall be prohibited.
12.7.5.4.5 Vehicles shall not be moved during exhibit hours.

 

[AlexDonkle]

There's a fairly limited number of ways stage floors are ever built. It's a little surprising the load ratings of the different types (e.g. sleeper spacing and deflection blocks like Bill mentioned) have never been standardized in the industry, instead of just being left up to the structural engineer for every project.

 

[BillConnerFASTC]

Theatres and performers are not standardizrtd so why the stage floor? Classical ballet, contemporary dance, orchestra, tap, band, drama, multi-use, or all of the above,road house or resident, pro or ametuer. All have different needs. The 125 to 150 is enough or too much for some, but the surface and resiliency requirements and budget vary a lot.

 

[AlexDonkle]

The requirements of the floor changes between different spaces, without a doubt, which means slightly different floor constructions are needed. But most stage floors seem to be variations on a theme, not reinventing the wheel for every new venue built (vegas showrooms and specialty theatres excluded). As this thread is an example of, not many people likely know the true limit of their own stage floor until they reach it.

The OP's floor is a very common construction for a stage floor built on concrete, I've seen it used before as others have I'm sure, but there's also no central database to to look up the max loading of that very commonly used sprung floor type without hiring a structural engineer to verify (or re-verify assuming a load analysis was done during the building's design phase). What I'm thinking is the floor loading equivalent to Clancy's batten loading diagrams. Measure the distance between pick-up points, and follow the chart to see how much weight you can safely point-load. The PLASA standard for stage floor shock absorption added a similar kind of table into the standard's Annex, but only for shock absorption of various floor constructions instead of loading.

 

[gafftaper]

Thanks Guys. We are going to go with a small prop car for "Greased Lightning" instead. And I'm in the process of trying to contact someone from the architect's to see if I can learn the load rating.

 

[BillConnerFASTC]

The requirements of the floor changes between different spaces, without a doubt, which means slightly different floor constructions are needed. But most stage floors seem to be variations on a theme, not reinventing the wheel for every new venue built (vegas showrooms and specialty theatres excluded). As this thread is an example of, not many people likely know the true limit of their own stage floor until they reach it.

The OP's floor is a very common construction for a stage floor built on concrete, I've seen it used before as others have I'm sure, but there's also no central database to to look up the max loading of that very commonly used sprung floor type without hiring a structural engineer to verify (or re-verify assuming a load analysis was done during the building's design phase). What I'm thinking is the floor loading equivalent to Clancy's batten loading diagrams. Measure the distance between pick-up points, and follow the chart to see how much weight you can safely point-load. The PLASA standard for stage floor shock absorption added a similar kind of table into the standard's Annex, but only for shock absorption of various floor constructions instead of loading.

The floor should be built to 125 or 150 psf - the codes changed and are moving back to 150. That's a lot and if pushing that, you should have an engineer anyway. The built up floor is based on span between sleepers and the grade and thickness of the spanning member, usually plywood. That is information than can be looked up on span tables, not that hard. The choice to use 24" centers or 16" or even 12" seems legitimate and not necessary to standardize. For instance, I'm using 12" o.c. 1X4's on flat in two existing situations where the slab exists and I don't have he room for our "standard" 4 1/8" thick floor. I'm interested in not forcing the user to lay planks for a lift truck or scissors lift. Unfortunately, the combination of various thickness and grades of plywood available for flooring is not as simple as line spacing on a batten.

 

[bobgaggle]

Off topic, but am I the only one who noticed they GLUED the maso down?!?! Was there that much faith that it would last for years and years? Thats gonna be a nightmare when it comes time to replace it.

Also I've never seen paper between layers of ply, anyone have a reason for this?

 

[venuetech]

I have a heavy Kraft paper between the layers on my flooring. As I understand it serves a number of purposes, one of which is to prevent wood to wood contact squeaks, slow vapor and moisture transfer.

http://www.wrmeadows.com/red-rosin-paper-multi-purpose-building-paper/

I also had paper between layers at a previous venue.

My father was an old school carpenter and used paper as a barrier on many occasions.

 

[BillConnerFASTC]

Are you sure its hardboard glued to plywood in the field during installation, as opposed to Plyron, which is plywood with outer veneers of hardboard all fabricated in the mill? I - and a number of folks - prefer plyron instead of separate ply and hardboard - because it is much more stable during humidity changes - never bubbles.

As far as paper, I researched this late last year when installing strip wood in my house. Lots of beliefs but if I had to bet, I'd say the paper was to stop dirt and dust from plastering sifting through between the subfloor - which was 1 X 6 boards. Second plausible reason was squeaks (not the sound technicians) and the paper provides a slip sheet between stripwood floor and subfloor - plywood or boards. I chose to put down red rosin paper on new plywood subfloor because it was old maple - reclaimed form a 1916 house being demolished - in my old house (1904) and rest of house had it (on board subfloor of course).

I don't see a reason for either red rosin paper or felt (tar paper) in a modern stage floor but other than a little cost, it doesn't hurt. We don't specify it - only a vapor barrier on top of slabs on grade so the moisture - concrete is drying and giving off moisture for at least a year - dosn't affect the wood flooring (so much).