Research Article Open Access

Robustness-Informed Seismic Retrofit Assessment of Existing Reinforced-Concrete and Stone-Masonry Buildings under Local Element Loss

International Journal of Digital Technology Driven Engineering Vol. 1 No. 1 (2026): Inaugural Issue Published 2026-08-27 DOI pending
  1. Chara Ch. Mitropoulou1*
  2. Matilda Kouramanou2
  3. Maria Dagalaki2
  4. Maria Gkara3
  1. Research and Development Department, Infersence Ltd., Bakou 1, 11524 Athens, Greece
  2. VELTION-Engineering Optimization & Applied Machine Learning Group (http://veltion.ntua.gr/), Institute of Structural Analysis & Antiseismic Research, Department of Structural Engineering, School of Civil Engineering, National Technical University of Athens, 9, Iroon Polytechniou Str., Zografou, Athens, 15780, Attica, Greece
  3. Research and Development Department, Innovasphere Ltd., 92B Hristo Botev Blvd., 4000 Plovdiv, Bulgaria

Corresponding author: Chara Ch. Mitropoulou, chara.mitropoulou@gmail.com.

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Keywords:

Structural robustness, Progressive collapse, Seismic retrofit, Reinforced concrete, Stone masonry, Alternate load path

Abstract

Seismic retrofit strategies are usually evaluated for the intact structure, even though the resulting changes in strength, stiffness, and load paths may also affect performance after local damage. This study presents a unified numerical framework for examining both objectives through two contrasting case studies: a six-storey reinforced-concrete (RC) frame and a load-bearing stone-masonry building. The existing RC building was assessed by nonlinear static pushover analysis under uniform and modal lateral-load patterns. Deficient members were strengthened with RC jackets, and the retrofitted structure was then examined after the notional removal of a ground-storey column. For the masonry building, three intervention schemes were considered: mortar-joint repair with shotcrete jackets (M1), mortar-joint repair with grout injection (M2), and mortar-joint repair combined with an RC ring beam and vertical prestressing (M3). Their seismic response was compared before four local wall-removal scenarios were evaluated using normal-stress and in-plane shear criteria. In the RC case, jacketing reduced the reported number of Life-Safety exceedances from 15 to 0; the reported performance-point target displacements also decreased, while base shear increased in the two Y cases and decreased in the two X cases. Because complete capacity curves were unavailable, the mixed performance-point base-shear changes were not interpreted as evidence of increased initial stiffness or ultimate resistance. Beam strengthening around the removed support was examined qualitatively as a means of improving the alternative load path. In the masonry case, M2 produced the largest nominal reduction in the selected elastic response measures under the adopted response spectrum. Under the adopted equivalent-continuum shell model, M1 and M2 remained below the source-study shear DCR threshold in all four examined scenarios, whereas M3 exceeded that threshold in every scenario. The results show that reduced intact-state response measures do not necessarily imply greater robustness. Retrofit selection should therefore include explicit assessment of damaged configurations and of the modelled response features governing demand after local element loss.

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