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Discussion in 'Calculations' started by Gsouth, Nov 12, 2021.

1. ### GsouthNew Member

Joined:
Nov 2021
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Hi Guys

I'm quite embarrassed and feeling rather sorry for myself having to ask for help to figure this out.

I had a few semesters of structural engineering at university (15 years ago), but have not touched an equation since and feel like a complete idiot now as I can't even remember how to solve for X in the simplest of equations.

Anyway, the problem I am trying to figure out goes as follows:

I am making a sliding hatch rail for my small sailboat and am trying to figure out how deep to make the member in order to avoid it breaking when someone stands on it.

I have attached a diagram of the profile, as well as the data for the wood that I am using below.

My thought process so far:

As I am not interested in how the element will fail, but rather when (i.e. only under how much force it will fail, I have decided to use it's weakest attribute, which seems to be its tensile strength perpendicular to the grain at 2.5MPa. (I also couldn't find any data regarding its rolling shear strength, which I actually think is exactly what's going to cause it to fail in this configuration.)

I then proceeded to calculate the moment at the bottom corner of the rebate which I got at 10Nm.

My thinking then was that when looking at the depth of the "shoulder" above ("X"), the bottom half would probably be in compression while the top half would be in tension, so I thought I should try to "solve for X" to figure out at what depth would the strength of the material be able to resist the tensile force indirectly placed on it by the external force.

I attempted a few equations to try and figure that out but got such wild answers that I gave up and decided to look for help.

What I am looking for is not so much the answer as it is the method for getting to that answer.
I hope there is someone here willing to hold my hand.

Iroko

Hardness

5600 N

Modulus of rapture

85.5 MPa

Modulus of elasticity

10100 MPa

Compression parallel to grain

52.3 MPa

Shear strength parallel to grain

12.4 MPa

Tensile strength perpendicular to grain

2.5 MPa

View attachment 1304

Cheers
G

2.
3. ### GsouthNew Member

Joined:
Nov 2021
Posts:
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The image I posted above doesnt seem to be working for me, so here is anoter go.

#### Attached Files:

• ###### Image 1.jpg
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