Stand design

[jusney]

Does anyone know of any online resource that I can use to calculate the approximate shear force required to break a plywood laminated beam of certain thickness and width?
THX

 

[rbredding]

jusney;581505 wrote: Does anyone know of any online resource that I can use to calculate the approximate shear force required to break a plywood laminated beam of certain thickness and width?
THX

there's not one that I know of.. (and I've been looking for years)

that's the main reason that tank bases are SO overbuilt so often.. people are scared when it comes to balancing over 1,500lbs on something that you made yourself..

if you're insistent on using steel, I'd recommend 4"X4"X1/4" angle iron (one at the front edge, one at the back edge) under the tank , but you're still going to run into an issue of transferring that load along the side end panels of the stand.


I've got my strengths of materials design book from college, but the issue isn't going to be design, it'll be prohibiting that design from impacting your area under the cabinet...

 

[jusney]

And justifiably so. The unmistakeable crashing sound of glass and the thought of 180 gal. of water in the house is enough reason to over build. I am even the more cautious because the project that I am working on is somewhat unique. I have a small designate space in the basement and I have two interest that are important to me. I love my aquatic hobby, but I do a lot of theological studies and require absolute peace and quiet for that. So, being that I don't have enought space for a dedicated office and fish room, I am designing an aquarium stand that has a retractable desk surface. The desk surface is 28"D X 56"W and the aquarium is 24"D X 72"W. I also need to have an extra 8" clearance beyond the back edge of the desk surface when it is in the retracted position (this is for the overflow pipes). the desk will be hinged on some extra heavy duty full extension hinges. Therefore the tank will be sitting in approximately 32"-24" from the front of the stand. In addition to that, there obviously has to be clearance for desk so no vertical support for the front edge of the tank. With all that said, I decided to build a frame similar to Aston Martin's and inaddition to that covering the sides with a solid piece 3/4" of ply instead of the usual thin skin. that should provide the required column strength. The top is where I am trying to decide on. It will either be a frame built from 3 pieces of 3/4" plywood laminated together whose dimensions are 2 1/4" X 4" (4" spanning vertically). this frame will have 3 of these laminated pieces running along the length of the tank, one on the back edge, one on the front edge and the other on the front of the stand. This frame will also have 2 perpendicular ties fron front to back aligned with the frame of the tank. All of this will be sandwiched between 3/4" plywood. The other option would be the same design, but with steel and they would be less wide.
OK, so what do all you "enginerds" think of my design?

THX

 

[jef4y]

Breaking the beam may not be your biggest threat. Deflection is more the concern for my builds... Keep that in mind and support accordingly.

 

[rbredding]

the deflection across a 4" deep framing member will probably be your downfall..

build it, then put it on cinder blocks and load it with everything heavy you can find at your house..

it's an inexpensive beam to re-design if you have to do so...

you've got to design the beams so that they are better than l/360 under load (otherwise, you'll stress the bottom of your glass aquarium... possibly cracking it)

 

[jusney]

What about the same dimension beam, but in steel?

 

[jusney]

Aston, I was kinda thinking that same , but like you said I am not an "enginerd" so I need to get as much info as possible before I sink myself. What I will do is build a sample beam, set its ends on concrete blocks and add weight to the very center to determind how much weight is required before it starts deflecting. This will give me a good idea of how much weight the beam will handle with the weight evenly distributed along its lenght.

 

[grouper therapy]

The beam would be much stronger if you have the room to make it 5" tall AND 1.5" WIDE. instead of 2.25" wide by 4" tall. You can also use a fletching (steel) plate between two layers of 3/4 plwood. We use to do this years ago before engineered lam beams were available. 1/16"thick piece of steel is equivalent to approximately 1" of wood beam assumming they are both the same height. when designing remember that taller beams are much stronger than wide beams.

 

[grouper therapy]

http://www.parr.com/PDFs/LP%20LVL%201.9E.pdf">http://www.parr.com/PDFs/LP%20LVL%201.9E.pdf</a>
This will give you the info you need. I have used something similar over the last 25 years to calculate loads on circular freestanding staircase.

 

[grouper therapy]

or this one

 

[grouper therapy]

http://www.engineersedge.com/beam_calc_menu.shtml">http://www.engineersedge.com/beam_calc_menu.shtml</a>
OR THIS ONE A LITTLE MORE IN DEPTH
And this one for steel beams if you think you need them
[IMG]http://www.toolbase.org/Design-Construction-Guides/Exterior-Walls/steel-beam-column-load">http://www.toolbase.org/Design-Construction-Guides/Exterior-Walls/steel-beam-column-load</a>

 

[rbredding]

grouper therapy;581642 wrote: The beam would be much stronger if you have the room to make it 5" tall AND 1.5" WIDE. instead of 2.25" wide by 4" tall. You can also use a fletching (steel) plate between two layers of 3/4 plwood. We use to do this years ago before engineered lam beams were available. 1/16"thick piece of steel is equivalent to approximately 1" of wood beam assumming they are both the same height. when designing remember that taller beams are much stronger than wide beams.

^^ again, Grouper knows what he's talking about..
I doubt that the fletching is required...


but again.. you had better make sure that your connection to the ends will hold 1/4 the weight of the tank..

I've seen screws/nails and even bolted steel connections shear off at the transfer point.. luckily in all cases, no one was killed..

 

[rededge2k1]

This framework will be more than enough...then you can just trim it out however you like:

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Have fun,
Dustin

 

[jusney]

Grouper, I think I should be able to go 5" tall, and thank you for the links. do you have any suggestions for where I could find this steel you are talking about?

Dustin, thank you for the mock up, pretty much dead on. I never thought of doing it that way, but looking at it now I think it would definitely work. The distance from front to back is much less and should subsequently be able to support more weight and deflect less. I would even be inclined to make those front to back runners thicker and let them rest on a dado that is deeper - not necessarily for distrust of your design, but more for my sleeping pleasure.

I really appreciate all the help I have received on this.

THX

 

[rededge2k1]

jusney;581679 wrote: I would even be inclined to make those front to back runners thicker and let them rest on a dado that is deeper - not necessarily for distrust of your design, but more for my sleeping pleasure.

I wouldn't go any deeper than 1/3rd the thickness of the plywood (1/4" : 3/4") if I were you. And use plenty of glue and a couple screws through the back.

But like grouper touched on before....you can't think of the tank as a point load, as it's spread out over a lot of plywood support. Plywood is insanely strong when stood on end. With a proper design and proper joints, plywood can hold any aquarium. It sounds like you have it under control my man.

Dustin

 

[grouper therapy]

ST metal works in Marietta ask for Keith mention my name David Kimbrell
I don't think you will need it but in case you do

 

[jusney]

Thanks Grouper. I went over the design using both scenarios - using front to back as the main support as well as the beam running along the front edge of the tank at 5" - 6". neither will work as they interfere with the desk operation. So I am back to looking at steel. I found a steel tube with dimensions that will work with my design and wanted to check with you guys. It's a 3.5" x 3.5" steel tube with 1/4" walls. I plan on welding a steel frame that will have three 72" pieces running the length of the tank, one on the back edge of the tank, one on the front edge of the tank and the other on the front edge of the stand. There will also be 3 or 4 ties from front to back. this will be sandwiched between to sheets of 3/4" plywood.
I am thinking this should be able to hold a ton, but we all know I am not an "enginerd"

THX

 

[rbredding]

(Great Idea Dustin.. )




Jusney,

good luck with the stand, I'd love to see your construction process.. make sure you take lots of pictures and post them in your build thread..

one thing that you can do to support the tube steel beams is to use an angle at each end and through bolt it to a piece of plywood on the ends (make sure you prime and paint the angles and tube steel with some rust inhibitive paint - higher gloss will protect better than flat)

you can cover the side panels with another layer to give it a finished look..

 

[jusney]

Well, the holidays are upon me and I will have to wade through the waters of christmas gifts and the like. So I will gather as much materials as I can and hopefully start work late december or early January. Wish me well.

 

[grouper therapy]

Ok early Jan. let's see it!!!