HI shr
if you use tied expansion bellow then effect of axial stiffness will vanish!
if you do the complex model about the EXP,you should need the axial stiffness ,and in some cases,it can absorb the deformation of the pipe between the two bellows ,and can check the force and moment of the ties.
but about the simple model of the draw- bar lateral expansion jonit,the EXP length is 1200mm,can you ever model the zero length ?i always model the 1200mm length,but about the 1200mm length model,if the the EXP weight is large,maybe the EXP weight distribute maybe isn't equal for the pipe system?what do you think it?
regards
zzw