Design a tension member w/ cross section

[General_Sax]

design a tension member w/ cross section...

Homework Statement

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?

Homework Equations

FS = UTS / R

[sigma] = F / A_o

A_o = L * w

The Attempt at a Solution

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 / A<sub>o[/SUP]

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.</sub>

 

[nvn]

General_Sax: First, where did 1279 MPa, and 862 MPa, come from? I do not see that in the problem statement. Secondly, MN/MPa = MN/(MN/m^2) = m^2. Or N/MPa = mm^2. Third, use the lowest allowable stress, not the average.

 

[General_Sax]

Thanks for the help!