Development of a Fragility Framework for Reinforced Concrete Frame Buildings Incorporating Nigerian Construction Quality Variability

Structural fragility functions are foundational components of earthquake risk assessment, yet those currently applied to Nigerian building stock are derived primarily from international datasets calibrated for construction quality standards and material variability that do not reflect Nigerian conditions. This study develops a fragility framework for reinforced concrete frame buildings that explicitly incorporates the statistical variability of construction quality observed across Nigerian building typologies, using field data from Abuja, Lagos, and Enugu in the North Central, South West, and South East geopolitical zones. Construction quality was characterised through an extensive database of 1,200 in-situ concrete strength test results, 450 reinforcement positioning measurements, and 300 joint detailing assessments collected from field investigations. A Bayesian hierarchical model was used to propagate construction quality variability into structural capacity distributions, which were then combined with demand distributions from nonlinear time-history analyses under 40 spectrum-compatible ground motion records. Fragility curves were derived at four performance limit states for three building typologies representing code-designed, partially compliant, and non-engineered construction. Results indicate that fragility curves for non-engineered construction in Nigeria predict probabilities of collapse under 0.1g peak ground acceleration up to 3.7 times higher than curves derived from regional Mediterranean datasets currently used as proxies, demonstrating the critical importance of country-specific calibration. The framework provides the first nationally calibrated fragility database for Nigerian reinforced concrete frames, representing an original contribution to probabilistic seismic risk assessment. Keywords: fragility framework, seismic risk, construction quality variability, reinforced concrete frames, Nigeria.