Due to powerful computers, you might consider modelling the actual geometry of the weld. This could be done in basic research but from an industrial point of view it is not practical, because the geometry of weld scatters greatly.
In the case of plate elements the weld is typically not modelled and the finite elements are arranged in the middle of the individual plates. Only if the weld has eccentric weld arrangements is the weld modelled. Examples are shown in the figure below. The main focus must be to take the structure’s change of stiffness into account and if it is greatly influenced by the weld then this must be considered.
Blas Molero Hidalgo, Ingeniero Industrial, Director IBERISA • 48004 BILBAO (SPAIN) WEB: http://www.iberisa.com Blog Femap-NX Nastran: http://iberisa.wordpress.com/