Seismic assessment of RC frames using nonlinear pushover analysis and variability propagation

Performance-Based Earthquake Engineering (PBEE) requires probabilistic treatment of structural capacity, yet current safety formats often rely on simplified approaches that concentrate all sources of uncertainty into global reduction factors (e.g. partial factors, global capacity factors, or confidence factors). The Knowledge Level / Confidence Factor (KL/CF) method, for example, applies uniform penalties to material strengths but cannot distinguish between different uncertainty sources or their varying influence across limit states. This thesis addresses this gap by developing a hierarchical framework for uncertainty propagation in reinforced concrete (RC) frames. The primary objective is to establish a rational procedure for determining the design capacity, the value with an assigned probability of not being exceeded, that satisfies the target reliability levels prescribed by modern seismic codes, specifically EN1998-1-1:2024. Two complementary methodologies are proposed: -Full-UP (Full Uncertainty Propagation): a rigorous, bottom-up approach that combines component probability distributions at hinge, column, storey, and frame levels using combination rules for series and parallel systems. -Sim-UP (Simplified Uncertainty Propagation): a pragmatic approach that applies First-Order Second-Moment principles to a global displacement model, capturing key system-level effects such as ductility and damage distribution. Both methods are formulated for distinct limit states (Damage Limitation, Significant Damage, Near Collapse), revealing how dominant sources of uncertainty evolve with the governing physical mechanism. Validation against Monte Carlo simulations on representative RC frames shows that Full-UP reliably bounds results, while Sim-UP provides accurate single-point estimates for structures with stable mechanisms. The outputs, median capacity and system dispersion, directly enable the construction of fragility curves and risk-informed decisions. This work therefore provides both a theoretical benchmark and a practical tool for seismic assessment, bridging the gap between advanced reliability theory and engineering application.