I have attached a rough ridge board (45x170) to support a bit in the eaves. I plan to mount an electric winch 50cm outside the last rafter.
The winch can lift 200kg (400 with an extra block). Will my ridge board handle this? Or should I replace it with a K24?
Is there anyone who can calculate this?
This is what it looks like:
0 1 2 3 4
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200kg
0. Fascia board
1. Winch mounting with brackets around the 170 (no screws in the beam)
2. Outer rafter about 50cm inside the winch
3, 4. Rafters cc120.
The ridge board is attached with brackets and anchor nails in every rafter so that the setup doesn't become a "seesaw."
edit: the image gets a bit skewed when I save. When editing the post, it looks okay. Hope you understand anyway.
/Micke
The winch can lift 200kg (400 with an extra block). Will my ridge board handle this? Or should I replace it with a K24?
Is there anyone who can calculate this?
This is what it looks like:
0 1 2 3 4
|-----------|----------------------|----------------------|
|
|
|
200kg
0. Fascia board
1. Winch mounting with brackets around the 170 (no screws in the beam)
2. Outer rafter about 50cm inside the winch
3, 4. Rafters cc120.
The ridge board is attached with brackets and anchor nails in every rafter so that the setup doesn't become a "seesaw."
edit: the image gets a bit skewed when I save. When editing the post, it looks okay. Hope you understand anyway.
/Micke
I have now received an answer from someone who can calculate. If anyone is interested, here is the answer (approximate):
Load:
- 200kg
- 50cm from the outermost rafter
Utilization rate of the wood:
- K12 wood - 91%
- K18 wood - 61%
Deflection with K12 wood: 6mm
Load on the outermost rafter: 3 kN
Upward force on the second rafter: 1.2 kN
Downward force on the third rafter: 0.2 kN
There is a downward force on the third rafter (number 4 in the sketch) because the rule is fixed in the second rafter (number 3).
I would never have guessed there was such an incredible difference between K12 and K18. Now I have replaced the ridge board with K24. It feels secure. Additionally, 6mm deflection could have caused problems for the ridge tiles, which could have cracked.
/Micke
Load:
- 200kg
- 50cm from the outermost rafter
Utilization rate of the wood:
- K12 wood - 91%
- K18 wood - 61%
Deflection with K12 wood: 6mm
Load on the outermost rafter: 3 kN
Upward force on the second rafter: 1.2 kN
Downward force on the third rafter: 0.2 kN
There is a downward force on the third rafter (number 4 in the sketch) because the rule is fixed in the second rafter (number 3).
I would never have guessed there was such an incredible difference between K12 and K18. Now I have replaced the ridge board with K24. It feels secure. Additionally, 6mm deflection could have caused problems for the ridge tiles, which could have cracked.
/Micke
I thought about it, but it felt difficult to do nicely. The entire middle-triangle in the trussed rafter is openable, so there isn't much wall left to attach these braces to.
With K24 lumber, I think it became a good solution. The blacksmith has made suspension brackets for the winch that go around the entire 170.
With K24 lumber, I think it became a good solution. The blacksmith has made suspension brackets for the winch that go around the entire 170.
Things to go up and down to the attic when the seasons change.
- Winter tires
- Bicycles
- Windsurfing board
- Garden furniture
- etc.
Additionally, the compressor is stored in the attic (compressed air needs to be routed to the workshop). You occasionally want to bring it down too.
Of course, none of these things weigh 200kg. But the winch handles up to 200kg, so I want to dimension accordingly. You never know what the next homeowner might want to winch...
- Winter tires
- Bicycles
- Windsurfing board
- Garden furniture
- etc.
Additionally, the compressor is stored in the attic (compressed air needs to be routed to the workshop). You occasionally want to bring it down too.
Of course, none of these things weigh 200kg. But the winch handles up to 200kg, so I want to dimension accordingly. You never know what the next homeowner might want to winch...
Cool! Who figured that out and what was used?
Best regards
Best regards
It was probably calculated with a simple calculation program by a designer... Definitely a simple calculation that all who are designers/building or mechanical engineers can do by hand...dogen said:
Probably this was calculated with a simple calculation program by a designer... Absolutely a simple calculation that all designers/building or mechanical engineers can do by hand..[/quote]Magnus_Nordmark said:
Calculating is not a major problem, but where can one find information on the wood grades' maximum allowable stress and E-modulus?
Ah, you seem knowledgeable. Where can I learn more about such calculations (at a home brewing level)? Any books you can recommend?
There are certainly many books on this available at libraries. Unfortunately, I don't have any titles to contribute. However, it's about basic knowledge in statics, moment calculations, etc... the basics of strength calculations. Look within strength/structural/machine. At this level, it's the same calculations, just different applications. Generally, we're probably talking about high school level and foundational for college...dogen said:
Ok, thanks for the tips! It would definitely be nice to have a bit more knowledge (though I say that about absolutely everything) 
Every person's small contribution leads to a complete world.. ;-)dogen said:Ok, thanks for the tips! It would definitely be nice to have a bit more insight (though I say that about just about everything)
Thanks for the tips! Will look for them!
Checkmattiasp said:
Single-axis problems, Technical Beam Theory, Bengt Sundström, Strength of Materials, KTH, Sthlm.
Unfortunately, I can't find an ISBN number.[/quote]
It was intended as a reference to ONE book.