DESIGN OF EARTHQUAKE RESISTANT MULTISTOREY STRUCTURE

This project presents the design of an earthquake-resistant three-storey hospital in Ijebu-Ode, Ogun State, Nigeria. The hospital was chosen as a case study because healthcare facilities must remain functional during and after extreme events. Although Nigeria lies in a low seismic zone with events around magnitude 4.0, recent tremors have shown that earthquake resistance should not be ignored. A geotechnical investigation revealed a soil profile of loose sand and silty clay in the upper layers, underlain by medium dense sandy soil between 10 and 20 meters. This layer was identified as the bearing stratum for the foundation. A pile–raft system was adopted to control settlement and improve load sharing, offering both safety and economy compared to raft or pile foundations used alone. The structural design was carried out using AutoCAD for architectural planning and ProtaStructure for analysis and detailing. Reinforced concrete elements, shear walls, diaphragms, and ductile detailing were provided to enhance seismic resistance. Analysis results confirmed that the foundation reduced settlements by nearly half, controlled lateral drift, and complied with Eurocode 8, BS 8110, and BS 8004 requirements. This study demonstrates that pile–raft foundations can improve the performance of multistory buildings in sandy soils, even in regions with low seismic risk. It provides a framework for safer and more resilient hospital design in Nigeria, contributing to knowledge by integrating seismic resistance into local practice.