Roycronos,
We use Seisab because it's the most efficient (and available) way of generating a seismic output (multiple licences and we've been using it since it's been in a DOS format). We also have SAP2000 (now re-branded as CSIBRIDGE) but it is much more time consuming than Seisab (because the...
Qshake,
We do something similar in Tennessee. We assume an initial linear stiffness spring for the soil behind the endwall, first assuming that the piles are effective at both abutments, and the soil spring only being effective at one abutment (if there is no expansion joint at either...