Seismosoft | Earthquake Engineering Solutions

Hi,
I am just wondering why we need to put a concrete cap on top of the pier when we create a bridge model? what will happen if not.

You need to put a concrete cap on the pier if a concrete cap exists in the real structure. One might occasionally see an older structure consisting of a pier which has a column under each girder and no cap. Such a system would still likely have a diaphragm to tie the beam ends together.

You should know what you are trying to model and include enough elements to accurately model that structure.