# Pin Jointed Truss Deflection Question

• 03-06-2021, 08:51 PM
christian Bendis
Pin Jointed Truss Deflection Question
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.
• 03-07-2021, 09:50 AM
Kelly Bramble
[quote]I think the vertical deflection will double from 22mm to 44mm - but how can I prove this with without detailed calculations?[/quote]

You can't..

Stress and deflection is typically not linear not is it simple and understood anecdotally.

Without a free body diagram, materials and engineering detail calculations - you don't know.

There is a 2-D statics modeler on Engineers Edge to check for yourself:

[url]https://www.engineersedge.com/calculators/statics-modeler/statics-2d-modeling.htm[/url]