Question

can you compare the main assumption as differences and common sides between the elastic limit state and ultimate limit states ?

Answer 1

elastic limit

elastic limit state is most traditional method of design.Working load is assume as design load. factory of safety is impose on material stress to get peremissible stress of the material. Linear variation of stress strain diagram is assume.

1. assumption of stress- strain diagram to be linear.
2. it doesn't incoporate the uncertainity of different loads acting upon it simultaneously.
3. large section size

ultimate limit

non- linear stress strain diagram material is consider

ultimate load calculated. working load is obtained by factor of safety of ultimate load. section size is small compare to working stress.

1. serveability not being fulfullied at working load because of excessive cracking and deflection
2. non linear anlysis is difficult.