i have modelled a trunnion on elbow in Caesar analysis.the type of restraint is specified at the bottom of the trunnion.i.e interface of trunnion base plate ans existing steel.for doing trunnion qualification should i consider the forces at the interface point between trunnion base plate and steel ? because sometimes the stresses and forces get reduced when a trunnion is modelled in Caesar. is this the correct way of analysis ?

For local stresses in the trunnion / elbow, you should use the loads at the top of the trunnion. Quite where the interface point is will depend on your modelling. Horizontal loads at both ends should always be the same in any case. Only the weight of the trunnion should affect the vertical forces at each end. Loads should only reduce when a trunnion is modelled because its inherent stiffness is included in the calculation. Or do you have another reason in mind ? Also, remember that by welding a trunnion to an elbow, particularly if it is near line size, you will change and possibly destroy the flexibility of the elbow itself. Your elbow modelling should reflect this.

this has solved my doubt

thanks MoverZ