Basic structural question

sounds solid to me fred

one thing i would do
is reinforce the corners of the 2×12’s
(with lags maybe)
so the swaying from the bike action
doesn’t work them loose

and maybe some ‘foot pads’
at the corners
to let it settle solid
and not rocker around
if the floor is uneven
or the frame warps some

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

Properly used wood is surprisingly strong I have made a setee wighing a lot with very small spindly legs whic would hold an elephant I think you will work it out.I would be more worried about it toppling over.have fun. Alistair

-- excuse my typing as I have a form of parkinsons disease

Interesting project, FredIV.

I feel the 2×12 rim joists are overkill. They’re not spanning anything, so all you need is a rigid leg to reach to the floor, right?

I’d use 3/4 plywood. Butt joints on the corners with a 1×1 glue block inside, the length of the joint. Countersunk screws make sense. Allow the finished height of the box to be 11 1/4 so you can add 3/4 thick feet on all four corners so it will sit stably on the floor.

For your “joints” you’ll need just one 2×4 running either direction. Glue blocks onto the plywood skirt to support it, and then some screws from the outside into the endgrain. Use polyurethane glue there if you’d like.

Then deck it, being smart about the way the plywood grain goes. You can get 3/4 ply with tongue and groove long edges, and that would make for tidy joints. Glue the deck on and it will hold all you need and more.

One caution: Provide a way to grab the thing so it’s not punishment to try to move it in. Could just be nice oval-ended slots on all four sides, or something like that.

Kindly,

Lee

-- "...in his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

I agree that 2×12s are not necessarily. I would just use 2×4s make a square and use some 3” deck screws to hold the corners together, then all you need is some 2×4s every 16” on center and screw them in from the sides and top with 3/4” ply and screw it on top, that will be strong enough to park a truck on. If you want to over kill it even more you can screw a piece of 3/4 ply on the bottom too. Like Lee said make sure you put some kind of handle on it.

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

Do you really need the 5’ width? The plywood is 4’ wide x 8’ long.

Lee, Jim – are you saying to construct the box out of plywood then span the 2×4’s across. I’m sorry for some reason I’m not visualizing it.

Fred
No I’m saying you make a frame like you would when you are framing a house wall lay it down and place plywood over the top. I’m a contractor of 25 years and have built platforms like this many times.

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

Got it. Then how would I raise it to the needed height of 11 1/4 without the flooring?

Fred:
My first question is – what is this platform going to be sitting on? Because it needs to handle the weight too. Ideally it would be nice if the entire underneath framing were sitting on structure beneath to distribute the weight. Otherwise, I am with other post that say use thinner material all around and create feet at corners and maybe even mid-span of the 6 foot length.

Dano

I was assuming that you were using the 2×12s for strength not that it was a requirement for your platform. Is there a reason it has to be that high? If it has to be that high for some reason then you need to have the frame be 2×12 as you had planned to start with but 2×4s are not strong enough for a 5ft span ,you should use 2×6s and Joist hangers.
You said you don’t want this to be to heavy but once you build it this way with 3/4 ply on the top it will add a good
30-40lbs.

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

Fred
Having been a carpenter forever (it feels like it any way) I am with a1Jim on this. With the size and the material its going to be heavy. I sure wouldn’t want to be moving it around. Just wondering why she wants to raise it up a foot.

-- My theroy in wood working will be. If I'm not enjoying doing it i won't do it.

She teaches a spin class called Core Ryder. The bike actually tilts left and right for added excersize features. The classroom is about 40 feet deep and she is at the head, facing the class. She wants to be seen and heard by all of the class attendees. I told her 12” was really high but she insisted that this is her “industry standard” (if there really is one). I wanted the platform to be wide enough so that she can get on and get off without the risk of missing the platform and injuring herself.

I was going to attached heavy casters to the back of the piece but they will never touch the floor when stationary. I was also going to add a handle in the front so that when the platform is lifted up the casters will roll along the floor. I’ve advised her on the potential weight but she seems pretty sure this is what she wants.

Okay, so suggest to use 2×6 joists instead of 2×4? This was my first thought but was trying to consider the weight issue. Should I still span the 2×6 12 inches on center?

I think you would be fine with 16” O C ,I still think you should use joist hangers to support the joist .

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

Thanks Fred. An excersize bike that tilts? I am going to have to google that.

-- My theroy in wood working will be. If I'm not enjoying doing it i won't do it.

Will definitely use the joist hangers, Jim. Oh and I take this class every tues and thursday. it’s a killer.

Thanks for all of the great advice.