Analytical Investigation of the Structural Adequacy of Existing Low-Rise School Buildings for Seismic Retrofitting in Plateau State

Plateau State, North Central Nigeria, lies within a low-to-moderate seismic hazard zone, and while earthquake events are rare, the structural vulnerability of existing low-rise school buildings to seismic loading has never been assessed, representing a gap in school safety research. This study analytically investigated the structural adequacy of 20 existing low-rise reinforced concrete school buildings in Jos North and Barkin Ladi Local Government Areas for seismic loading demands derived from the Nigerian Seismic Hazard Map and the Eurocode 8 design spectrum for low seismicity zones. Structural geometry, element dimensions, reinforcement details (from partial drawings and in-situ measurements using a ground-penetrating radar), and material properties (Schmidt hammer strength estimation) were documented for each building. Structural analysis was performed using capacity spectrum method implemented in SAP2000. Building capacity was compared to the seismic demand for the 475-year return period earthquake. Results showed that 75% of assessed buildings had inadequate lateral load-resisting capacity against the design seismic demand. The primary structural deficiencies were inadequate column-to-beam stiffness ratios (soft storey potential), insufficient reinforcement continuity, and lack of seismic detailing. Mean ground-floor column compressive strength was 16 MPa, below the 25 MPa minimum for seismic zones. Cost-effectiveness of RC column jacketing and wall infill retrofitting strategies was estimated. The study recommends a phased seismic vulnerability assessment and retrofitting programme for all public school buildings in Plateau State.

Keywords: seismic vulnerability, school buildings, structural adequacy, retrofitting, Plateau State