Nonlinear assessment of progressive collapse in irregular buildings triggered by pulse-type near-field earthquakes

This study evaluates the progressive collapse behaviour of reinforced concrete buildings with structural irregularities subjected to pulse-type near-field earthquakes using a nonlinear dynamic analysis framework. Three-dimensional five-storey building models incorporating mass and stiffness irregularities are analysed by explicitly simulating edge and corner column removal scenarios. Nonlinear time history analysis is conducted using recorded near-field ground motions to capture the combined effects of seismic excitation and sudden column loss. Structural performance is assessed through plastic hinge development, inter-storey drift, and displacement response. The results show that irregular buildings experience substantially higher collapse vulnerability compared to regular configurations. In the edge column removal scenario, stiffness-irregular buildings exhibit an increase in maximum storey drift of approximately 3–4% compared to regular buildings, whereas the inclusion of masonry infill walls leads to a nearly 10–12% reduction in drift demand. Roof displacement demand increases by about 20% in stiffness-irregular buildings relative to regular buildings, while buildings with masonry infill walls demonstrate a reduction of nearly 30–40% in displacement demand. Mass-irregular buildings show a pronounced upward propagation of damage, with collapse-prevention-level hinges extending up to the fifth storey under near-field excitations, particularly during the Kobe earthquake. Across all building configurations, edge column removal consistently produces higher displacement demands than corner column removal, with first-storey displacement demands increasing by approximately 2–5%. Although masonry infill walls significantly improve global drift and displacement performance, the resulting stiffness discontinuity causes severe damage concentration at the ground storey. The findings highlight the critical influence of structural irregularities and near-field seismic characteristics on progressive collapse behaviour and underline the necessity of incorporating nonlinear dynamic collapse assessment in the seismic design of irregular buildings.