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# Pin Jointed Truss Deflection Question

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## Pin Jointed Truss Deflection Question

(OP)
Hello all

I was hoping someone could help with the following:-

I have a pin jointed truss (all members are joined by frictionless pins and load is only applied to the joints), supported by 2 x pin jointed supports.

If my pin jointed structure was loaded solely at a joint with 200kN which resulted in a vertical deflection of 22mm with a Youngs modulus of 150kN/mm^2.

If I then doubled the load to 400kN but kept everything else the same then what would happen to my deflection?

I think the vertical deflection will double from 22mm to 44mm - but how can I prove this with without detailed calculations?

I know that if I halved the young's modulus then this would be result in the deflection doubling.

Is there any other ways of proving that the deflection will double (assuming it does double)???

Thank you.

### RE: Pin Jointed Truss Deflection Question

If the problem defines the system as linear, the answer is in the question. By definition, doubling load doubles deflection in a linear system.

How the questioner wants it answered depends on what you're learning at the moment. Can you simply say the first 200 kN causes 22mm, and the second 200 kN also does anothet 22mm? Or are they after a virtual work answer? Or something else you studied this week?

### RE: Pin Jointed Truss Deflection Question

Well, pinned supports on both ends is very likely not going to match the real world because it can give odd results, so when using that model who knows what might happen.

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