Rectangular Tubing as a Floor Support

OK, a king waterbed will exert about 50# ft² for a total, empty, static bed load of one ton.

Size, weight, number and activity of occupants will add to that figure.

I'd make a couple of T posts from your tubing and run them from the floor to the joists under the bed's location.

What Crabtree says.

I haven't said anything to this one yet.

I was anticipating and referring to the good moaning part.

First of all, get a Building Permit from the appropriate government authority/ies...

Generally speaking, you should first figure out how much of a load you can reasonably expect the existing floor framing to support, on it's own, to start with.

Using tubular lengths is generally more costly than rectangular joists, on-edge, because tubes are less efficient at carrying flexural loading than standard joists of equal lateral cross-section.

In any case, 2" by 6" joists are relatively shallow, and putting tubes on top of the floor sheathing will tend to add new concentrated loads on top of the flooring.

Consider adding additional 2" x 6" joists on both sides of the existing joists to better resist bending loads on the existing floor.

In any case, make sure your liability insurance is enough to cover a big lawsuit, for when say, some kids decide they want to see how (springy) the floor really is ...

There's reasons why Landlord's don't allow waterbeds in rentals and if your the home owner, you should consider another type of bed.

Lyn has a good suggestion of vertical supports, Mr Guest also has a good suggestion of adding doublers to the existing joists.

Without having a layout of the room location and center supports of the floor joist, it's difficult to give you a definite plan of action

What I've done in the past with a situation like what you want to do is, add 1/2" plywood shear plates glued to the floor joist using a good quality glue like Plastic Resin Glue.

If the floor joist are boxed, you should remove the cross pieces and replace them after the glue is set.

The plywood grain has to be placed perpendicular to the joist grain and should be nailed or screwed in a "Δ" and "∇" pattern so that they form a triangle every 8-10 inches apart . You only need #6 screws or nails 1 1/4" long to hold the shear webbing in place until the glue dries. Then add the vertical supports accordingly.

I would just use 2 ea 4x4"s and 4 adjustable floor jacks, build a support structure directly beneath the bed shaped like a standard waterbed base...

http://www.homedepot.com/p/Tiger-Brand-Super-S-Series-8-ft-4-in-Jack-Post-J-S-100/100022783

For a 17' span you would need to go with an I-beam or a lattice beam....

My money is with Solar eagles proposal. I beam or RHS would work. 4" drop would not be as good as 6" drop, but I assume you are attempting to keep height obstruction to a minimum. A good explanation can be found here:

http://www.learneasy.info/MDME/MEMmods/MEM30006A/Area_Moment/Area_Moment.html

This sounds like one of those schemes that has the potential to go horribly wrong. I'd change the plan, then, I'm funny that way.

If you need to keep depth to a minimum for head clearance search for LVL. 6" x 3" LVL joists inter spaced between existing joists may work. I say MAY because i'm too lazy to check the span tables. I CAN say that your existing floor doesn't pass code for Australian buildings. You could put a load bearing wall/cupboard/closet in the centre of the basement and probably meet code. Otherwise a steel beam made from Universal Column through the centre. This HAS to be spec'd by a structural engineer in Oz, dunno about where you are. Jim

You don't need an Engineering website. You need to pay for a qualified local structural engineer to design something in accordance with local building codes, then.

The problem with your answer is that of avoiding liability.

The OP is looking to see if this approach has any merit. He must get a permit, which will included a sign off either by his building officials (and they won't once steel is used as they can only use "cookbook" IBC tables for wood construction), or a licensed local PE to give approval to any use of steel.

I'm not a PE, and I take no liability for free information to: this approach being workable.

I bet the bigger issue is installation of any cross beam wood or steel, as the floor has sagged over the last 100 years and pushing this back up will be extremely difficult. And these way to shallow of steel beams will be "preloaded" to where they will be bent by the installation attempt.

Maybe you should clarify how much clearance you currently have under the bottom of the existing joists...

I'm still in the planning stage I'm still in the planning stage and getting my line of actions in proper order before getting a permit for this project Thank You for all your replies and input.

The house was built in 1919, so current code and use were not of thought when constructed.

Upon reviewing current wood floor joist load limits for what is constructed, the MAX span should be 8' to 9' for a common dwelling use.

I was hoping to support the existing floor without losing head clearance (6' 10") and maintain a full open area. Thank you for bringing to light I have been dreaming.

I came across the 4x3x.250 at no cost and wise to incorporate it into the support of the above room with the intend use.

Plan B: Again using 2 4x3x.250, welded together, with support at both ends and 2 vertical supports giving 4 equally spaced points of support. This is to placed at the center of the 17.5 span, perpendicular to the joist run.

Thank You ignator, for providing a detailed analyst of my situation and the load/flex projections. At this time, I'm still in the planning stage and getting my line of actions in proper order before getting a permit for this project. This is only one of the concerns to be addressed during the complete project.

Again, Thank You to all who contributed in bring insight how to properly address this issue.

IdKid

But, in what State and/or Country is this (renovation) to take place???