Structures & Materials - Cranes and Steel Cable

[codz30]

Homework Statement

A crane consists of a crane arm which is held in place and moved by strong steel cables.
The crane arm is a truss structure, which is a rigid framework of quite thin steel beams welded together, forming many triangles.
The cables are made of steel and they are not one piece but consist of many thin strands of steel plaited together, in a way similar to most ropes. The cables carry very heavy loads but fortunatley they are almost perfectly elastic.

i) What is one reason that a truss structure like this is nearly as strong as a solid beam of about the same size?
ii) Why is the cable made of thin strands plaited into one thick cable stronger than a cable made of solid steel?
iii) Explain the meaning of 'elastic' with reference to the cable.

The Attempt at a Solution

i) The shape of the structurem using triangles, spreads out the load. Triangles are strong structures.

ii) Because the steel cables share the load better.

iii) It means the cables can spring back into shape.

I don't really think my explanations are correct, but it's the best I can think of.

 

[LowlyPion]

What about the cross sectional area for a beam? What about the weight of trussed lattice versus say a solid beam?

http://en.wikipedia.org/wiki/Beam_(structure )

Elastic suggests that it stretches uniformly depending on load doesn't it? Like a spring?