Implementation of a substructure method to analyse soil-structure interaction at an existing 10-storey reinforced concrete building

In earthquake-resistant design, structures are usually assumed to be fixed at their bases. Although in some cases this assumption may be realistic, in other cases it is neither reasonable nor conservative and the consequences can be significant. Many investigations of soil-structure interaction (SSI) in recent decades have been related to prototype frame buildings. On the other hand, relatively few investigations of SSI have considered existing structures and structures of mixed systems. This work investigates SSI in a 10-storey reinforced concrete structure built in the 1970s in Ohrid, North Macedonia. The building is part of Ohrid’s 3D seismic network and is instrumented in the soil profile, foundation structure and two storeys. Thus, it provides an ideal example to investigate SSI. The interface between the soil and the structure is substituted with springs to consider the flexibility of the connection between the soil and the structure. The results of the flexible base structure are provided in terms of the reduced demands (reduced response spectra and the elongation of fundamental vibration period) and these are compared with the fixed base counterparts. The findings of this study contribute to a better understanding of SSI effects in dual systems and provide valuable insights for more accurate seismic design practices incorporating SSI.