Impact of Building Code Transition on the Seismic Resilience and Fragility of Reinforced Concrete Buildings: A Performance-Based Assessment

Quantifying how transitions between successive seismic design codes affect structural resilience and fragility is essential for evaluating whether updated design provisions translate into measurable improvements in earthquake performance. This study evaluates the impact of transitioning from SBC-301-2007 to SBC-301-2018 on the seismic resilience of reinforced concrete dual-system buildings. Representative 10- and 20-story structures were designed according to both editions and analyzed across four seismic zones (Magna, Al-Bada, Abu-Arish, and Medina) using Response Spectrum Analysis (RSA) and Nonlinear Time History Analysis (NLTHA) with ten spectrum-matched ground motions. Seismic performance was assessed in terms of base shear, inter-story drift, fundamental period, and fragility-based damage probabilities. Results show that the 2018 edition substantially increases seismic demand in high-hazard regions, with base shear rising by up to 92% for 20-story buildings in Al-Bada and 50% in Magna. Conversely, base shear decreased by 6–11% in low-to-moderate seismic zones, demonstrating the region-dependent effects of the revised code provisions. NLTHA results indicate that in high seismic regions, 20-story buildings designed under SBC-2007 reached maximum inter-story drifts of 78–103 mm, corresponding to responses between the Life Safety (LS) and Collapse Prevention (CP) thresholds in Al-Bada and exceeding the adopted CP threshold in Magna. In contrast, SBC-2018 designs limited the maximum drift to approximately 36 mm, corresponding to a response between the Immediate Occupancy (IO) and Damage Control (DC) thresholds. Fragility analysis further demonstrates improved performance: at PGA = 1.0 g, the probability of exceeding the Collapse Prevention (CP) performance state for the 20-story building in Magna decreased from approximately 0.45 (SBC-2007) to 0.30 (SBC-2018), representing a 33% reduction in CP exceedance probability. Overall, the transition to the 2018 provisions enhances seismic resilience and reduces structural fragility, particularly for taller buildings in higher-hazard regions, while buildings designed under the 2007 edition remain adequate in lower-hazard regions.