Question

1. How does the lateral movement of the roller support impact the measured vertical deformations?

2. Discuss the advantage of considering the extra available strength due to the plastic beam theory when designing structures.

Answer 1

1).

Allowing lateral movement at any support by means of roller support always cause increase in vertical deflection.

This lateral movement also prevents any formation of fix end moment due to fixity at that end.

2).

First of all, in elastic theory we allow a certain load for a beam, by considering that beyond this point, beam or member will stretch beyond the elastic limit. But in actual practice we see that that beam/member is able withstand much more load than that corresponding to it's elastic limit. So it means we don't use the full strength of member in elastic theory, or we can say that we under estimate the capacity of beam/member. And the due to such under estimation of load carrying capacity of member we need to provide heavy/bulky member.

But in plastic theory, extra available strength is considered, and henced more load is allowed to same member. Which results in relatively thin/light members. Use of such light members is good for economy.