Lezione 5: Stiffness limited design

Question 1

What are the 3 common modes of loading?

Answer 1

1 - Tie with a circular cross-section loaded in tension. Actually the shape of the cross section does not matter, because the stress is uniform across the section.
2 - Beam with rectangular cross-section loaded in bending
3 - Shaft of circular cross-section loaded in torsion

Question 2

How does the cross section influence the moment of area?

Answer 2

Thanks to the shape factor (fi). By reshaping the cross-section of a beam, it’s possible to increase I (thus increasing stiffness) without increasing the total area. The ratio of I for the shaped section that for a solid square section with the same area is defined as the shape factor fi. Shaping is also used to make structures lighter: it’s a way to achieve same stiffness with less material.