Load-bearing capacity of aluminum L-beam

[Violina]

If I read aqvisdeck's brochure correctly, they use 160x61 mm aluminum profiles (it does not specify which type) with a spacing of 450 mm. In your case, it would be ten or eleven beams. The maximum span without additional reinforcement beams is 6400 mm between the wheels, so you would definitely need extra reinforcement beams. Unfortunately, I can't find any details about their extra beams except for a picture. So, aluminum is possible, but it requires a lot more than just reinforcements at the edges.

Their base construction weighs 19 kg/m^2, which with decking becomes about 40 kg/m^2 (according to their specification). In your case, it would be approximately 1500 kg (8.4*4.2*40=1411.2). About what your solution weighs as well. They dimension for 100 kg of snow per square meter, which with self-weight in your case would be approximately 5 tons (8.4+4.2*140=4939.2).

Based on these figures, I would dimension the deflection after 1500 kg (given that the insulation doesn't absorb moisture and cause issues) and dimension the strength for 5 tons (refrain from moving the roof with load).

Unfortunately, aqvisdeck doesn't specify deflection, but one can conclude from their clearance between the bottom edge and the wheel track that the deflection is less than 30 mm (the deck is 195 mm high, including wheels but without decking). The deck must never be rolled with load.

With these starting values, one could calculate different solutions, such as:
- Two strong (cambered) steel beams
- Three or more (possibly cambered) beams (with enough, maybe aluminum, otherwise steel)
- Self-supporting sheet metal

What do others think, are the values I've taken from aqvisdeck a reasonable starting point?

Yes, but one probably still needs to dimension for a higher deflection than just for the 1500 kg, because I believe the impact in the middle of the cover would otherwise be VERY significant when it is closed and there is snow on it...

The risk is that the material ages (at least steel and other metals), which can be simply put as even if you don't reach the material's yield limit, if it's bent for long enough, you will get a permanent deflection of the material...

When storing material in the workshop, for instance, it's important that it has support with X-meters distance (depending on the type of profile) otherwise it will become "banana-shaped"...

 

[Huggedugge1]

We live in Kungsbacka and the roads are closed if more than 5 cm of snow falls in one day….

 

[Violina]

What does that have to do with the construction of a pool deck???

 

[Huggedugge1]

What does this have to do with the construction of a pool deck???

Share the previous post's opinion that maybe one shouldn't count on snow load...

 

[Violina]

You should always account for snow load, because if it snows it will definitely stay on your deck.

An undersized deck is the last thing you want, right?

Otherwise, you might as well keep what you have.

 

[Huggedugge1]

You should always account for snow load, because if it snows, it will definitely stay on your deck.

An under-dimensioned deck is the last thing you want, right?

Otherwise, you might as well keep what you have..

Why do you even comment when you've already said you can't or don't want to suggest materials and dimensions? Boring...

 

[Erik Lindroos]

Now, if someone could verify the calculations to ensure no mistakes slip through. I'm assuming 1500 kg for maximum deflection of 15 mm (and 5000 kg to check the bending stress).

Minimum moment of inertia
I = (5*1500*9.81*8400^3)/(384*200000*15)=37854337.5 mm^4 ~= 3785 cm^4

Option 1.
A VKR tube on each side. 200x100x6.3 is just under with 2x1851=3702 cm^2. However, VKR 200x100x8 works with a bit of margin, 2x2269=4538 cm^4 (gives deflection of 12.5 mm). The maximum moment M for 2500 kg load per tube is Q*L/8=2500*9.81*8400/8=25751250 Nmm. Bending resistance W=227000 mm^3 provides maximum bending stress of M/W~=113 N/mm^2. This should give a safety factor of 2+ against the yield strength. The tubes weigh about 320 kg each.

Option 2.
Several VKR 160x80x5. Five are just under, but six tubes work. Deflection is 12.6 mm for a total weight of 1500 kg evenly distributed. Maximum bending stress of 91 N/mm^2 for a total load of 5000 kg. The tubes weigh about 162 kg each (972 kg total).

In hindsight, one can see that the weight might make it difficult to maintain 1500 kg, at least in option 2. I've only calculated the longitudinal tubes.

 

[Derbyboy]

Option 1, do you mean two pieces of 200x100 VKR with a span of 840 cm on each long side of the pool? In between, floor joists with a span of just over 4 meters are placed.

 

[Erik Lindroos]

Option 1, do you mean two 200x100 VKR with a focal length of 840 cm on each long side of the pool. In between, floor joists with a span of just over 4 meters are placed.

Yes, so it places some demands on the cross beams. That also needs to be calculated...

 

[Erik Lindroos]

Alternative 1, do you mean two pieces of 200x100 VKR with a span of 840 cm on each long side of the pool? Between them, floor joists are laid with a span of just over 4 meters.

Upon further reflection, you don't always need such a thick support on the side that always has support.

 

[Derbyboy]

Is a VKR the type of beam that is the stiffest?

I'm thinking that an HEB might be stiffer….

 

[Violina]

I had already placed a tube at the far end and one in the middle, allowing one long side to be supported by the edge (as it is now).

So each tube only needs to "just" hold 1/3 of the deck's weight.

Hence my lighter dimensioning..

 

[Erik Lindroos]

Is VKR the type of beam that is the stiffest?

Thinking mostly that an HEB might be stiffer….

Pure "bending stiffness per kilo" is probably best with IPE. There are several alternatives. If one now "agrees" on which moment of inertia is required, then it's easy to check tables.

 

[Violina]

Is VKR the type of beam that is the stiffest?

I'm thinking that an HEB might be stiffer….

It's almost twice as heavy too..

 

[Erik Lindroos]

I would have placed a pipe at the far end and one in the middle, allowing one long side to be supported by the edge (as it is now).

So each pipe only needs to hold 1/3 of the deck's weight.

Hence my smaller sizing..

I realized it after the previous comment, so it's an important point.