What size Aluminum angle?

I am trying to figure out what size Aluminum angle I should use to frame the decking for my boat.

If I put Aluminum angle trusses spaced every 16 inches, could I use 1 x 1 x 1/8 angle for the trusses? Does going to 1-1/4 x 1-1/4 x 1/8 make it any stronger, or would I have to upsize the 1/8 to 3/16?

Is there an easy way to calculate, or a rule of thumb for spans, deflection under weight, etc?

Ken

Glad youve joined, but is there any way to join all these threads so all the information is in one place?

Sorry, I don't know of any way to join the threads.

It's funny, I split the topics into multiple threads because I once got yelled at on a different website for combining too many topics in one thread. It was explained to me that for purposes of later searching, it is best if a new topic is created once the original question is answered.

It seemed to me at the time that the topics were distinct - 1) how to mechanically fit angle to make a joint, 2) how to best weld angle, and 3) how to size angle to support weight. Or course, they all have the same theme - angle.

I will leave it to this forum's administrator to decide if the threads should (and can) be combined, or should be left separate. I'm OK with either choice.

Ken

I'm sure most of us over engineer our decks. I used 1 1/2 x 1 1/2 x 1/8 angle spaced roughly 15" apart. Combining that with 1/2" plywood for decking and mine is rock solid. Could I have used 1 1/4" instead... probably but I wouldn't have gone down to 1" x 1". 1" angle would need a lot of 'legs' going down to the floor to support any amount of load.

Ken, I didn't mean anything bad by it - I am just a fan of keeping things in one thread, that's all lol. All of your questions are important, so it's not a big deal. Maybe I was a bit jumpy, haha. Anyway, good luck!

I'm using 1 1/2" x 1 1/2" x 1/8" tubing and angle on my project. So far, I have the rear deck 95% completed. I haven't attached the deck yet. I'll wait until I get the bilge pump mounted. It may look overbuilt, but I could feel some flex in the 1/8" plate before I added two additional support tubes. There's no flex now.

Kurt

Sure does look solid...Kurt.
Nice job.

kglade said:

I am trying to figure out what size Aluminum angle I should use to frame the decking for my boat.

If I put Aluminum angle trusses spaced every 16 inches, could I use 1 x 1 x 1/8 angle for the trusses? Does going to 1-1/4 x 1-1/4 x 1/8 make it any stronger, or would I have to upsize the 1/8 to 3/16?

Is there an easy way to calculate, or a rule of thumb for spans, deflection under weight, etc?

Ken

Click to expand...

Ken,

How long will your free spans be? what are you sheeting it with for flooring, and how big will the deck be?

Brad:

Sorry for the late reply.

I found some software tools to help me make the calculations. The questions you asked about free spans, deck thickness, etc. are to me, a circle. I'd like to pick the free spans and deck thickness and size that would give me the "right" design without overdesign.

Anyway, I found that structural guys try to keep deflection in decks and balconies to less than 1/240 or 1/360. That means less than 0.1 inch deflection in a 36 inch span for 1/360.

I used beamboy to calculate deflection for a 300 lb point load, midway between my beam support points, and by trial and error found the answers I was looking for. I had to use "engineering power tools" to calculate the moment of inertia for the various angles and channels I was considering. Beamboy needs to know the moment of inertia for the beam, as well as the modulus of elasticity (10, 000, 000 /in2 for aluminum). Note, engineering power tools can do the deflection calculation, too, but does not display it graphically like beamboy does.

I know the addition of decking, especially vertical walls, makes everything stronger, but I don't know how to calculate that. I also haven't figured out how to calculate the deflection of a sheet of plywood or aluminum supported by beams.

beamboy is freeware. engineering power tools is $24.95 but works for 30 days for free but won't print or save data.
beamboy can be found at https://www.geocities.com/richgetze/
engineering power tools can be found at https://www.pwr-tools.com/

Anyway, to make the story complicated and real-world, I came across 84 feet of aluminum channel, 1 x 3, for free, and am trying to design the structure around this. I am puzzling over how to make the joints, but that is in another thread.

I am on the fence about aluminum vs. wood decking; today, I am leaning toward wood. I am thinking 16 inches between beams (like in a house) so the floor should deflect about like it does in a house. There is a really good picture here https://www.johnbridge.com/vbulletin/showthread.php?t=8921 that shows how grain direction affects deflection in plywood.

Ken

Here are a few pics of how mine was done. I did not do this, boat was custom built by boat builder in Arkansas. I wished I could weld aluminum......

yes that is what i used for mine and it is solid

I'm running into the same question years and years later. Not sure if anyone even sees the threads anymore. So i have a bunch of 1/16th" thick L angle thats 1"x1" and I'm gathering the general concensus is that this is not strong enough material to build a front deck with.

Brad Newman said:

I'm running into the same question years and years later. Not sure if anyone even sees the threads anymore. So i have a bunch of 1/16th" thick L angle thats 1"x1" and I'm gathering the general concensus is that this is not strong enough material to build a front deck with.

Click to expand...

I don't have any special knowledge, but it seems it all comes down to the spans. I would use 1/16" if well supported short spans (16" max??). This is really seat of the pants on my part. Hopefully someone with hands on experience will chime in.

What material is the angle? What is the max unsupported span you are considering? What is the construction of the decking?
https://www.omnicalculator.com/construction/beam-deflection

You typically get better strength with a wider piece than with a sticker piece. So, a 1-1/2 X 1-1/2” angle X 1/16” thick will be stiffer than a 1X1 if secured so it can’t twist.

If you have 1x3 angle, that is very strong with the 3” leg facing down- use it!

Plywood decking is comfortable, easy to use and forgiving.