The two are design methods
working stress method: @ the stress in an element is obtained from the working or service loads and compared with permissible stresses.
@ the method follow linear stress - strain behavior of both the materials.
@here service or working load is used in the whole design.
@ modular ratio can be used to determine allowable stresses.
@ factor of saftey are used in WS.
@ ultimate load carry capacity can not predicted.
@ drawback is result uneconomical section. And
@ now we usd mostly in temporary work.
limite state design ;method is recently used method and
@ stress here obtained from design load compared with design strength.
@ this method follow linear strain r/n ship but not linear stress.
@ the ultimate stress of a materials itself are used as allowable stresses.
@here we use partial saftey factor for material and loads are used.
@here loads assessed with reasinable probablity of occurance.