Soil-structure interaction effects on the static disproportionate failure resistance of reinforced concrete frames: A staged numerical study using finite-element and finite-difference methods

The present numerical investigation evaluates how Soil Structure Interaction (SSI) affects the static Disproportionate Failure (DF) behavior of Reinforced Concrete (RC) frames subjected to localized column removal. The numerical framework uses Finite Element (FE) modeling in SeismoStruct for the RC superstructure and finite difference modeling in Fast Lagrangian Analysis of Continua (FLAC) for the integrated soil, foundation, and frame system. A representative RC frame was first defined to assess the structural modeling procedure. The framework was then applied to a Two Dimensional (2D) RC frame under first story Case R1, Case R2, and Case R3 removal scenarios. Nonlinear static pushdown analyses were performed to determine intact and damaged failure load, displacement response, and relative capacity loss. A parametric investigation considered foundation thickness, soil density, soil type, subsoil layering, and groundwater level. The main contribution is a staged FE and finite difference framework that compares fixed base and soil supported representations and quantifies how foundation and ground conditions modify the relative loss of static failure capacity under multiple column removal scenarios. The sensitivity ratio was defined as the normalized reduction in failure load from the intact state to the damaged state. Case R3 column removal produced the largest relative capacity loss, while Case R1 removal produced the smallest. Soil and foundation conditions altered structural displacement, vertical soil stress distribution, and the relative loss of static failure capacity within the adopted numerical models. The findings apply to the adopted static pushdown procedure, 2D frame representation, shallow foundation model, selected soil properties, and single first story column removal scenarios. Accordingly, the reported results represent static column removal response and do not constitute an assessment of dynamic seismic performance or earthquake induced failure probability.