You are to design a tension member....

[General_Sax]

You are to design a tension member (square rod) with a cross section to carry a mass of 575 000 kg with a safety factor of 2 against yield and a safety factor of 3 against static fracture (overload).

a) What is the design stree that you will use for the application? Why?

b) What are the appropriate bar dimensions for use?


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FS = UTS / R

[sigma] = F / Ao

Ao = L * w

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FS = 1279MPa / 3 = 426.33333... MPa ~ 426 MPa
that's the design stress considering static fracture

FS = 862 / 2 = 431 MPa
that's the design stress consider yield stress/strength

So, I'm considering using a design stress that is the average of these two values, which would be: 429 MPa

I'm just confused, because we haven't done anything like this in class.

Now for part b)

[sigma] = F / l*w

F = 575 * 103(kg) * 9.81(m/s2)
F = 5.641 MN (mega Newtons)

429 = 5.641 MN / Ao

Ao = 13148.6014 MM (mega meters? I'm not sure about the units on this one)

l = w = 6574 MM

Please help and thank you; ie, does this look right to you?

[Studiot]

Of the three stresses (426, 429 & 431) you have calculated only one gives a safety factor of 3 against fracture.

Which one is it?

This is the only one which satisfies both the safety factors of at least 2 and at least 3.

I'm sure if you check the units of (426, 429 & 431) in part (b) you will be able to calculate a more sensible area.