This paper focuses on overcoming difficulties associated with the assessment of a multi-story reinforced concrete frame building constructed in several phases over time, with an irregular layout. Trying to develop a coherent, safe and sensible design in such a case is indeed a challenge for structural and geotechnical engineers. The retrofitting problem is made worse by incomplete data, a building with shallow and deep foundations, and architectural "re-purposing" of the entire structural assembly. A state-of-the art seismic performance evaluation according to Eurocode 8-3 is presented as a case study, with special emphasis on the topics of numerical modeling and foundation modeling. Potential modeling simplifications are considered as well.