Revisiting Nonlinear Modelling Approaches for Existing RC Structures: Lumped vs. Distributed Plasticity
Hüseyin Bilgin*, Bredli Plaku
Department of Civil Engineering, Faculty of Architecture and Engineering, EPOKA University, Tirana, 1032, Albania
* Corresponding Author: Hüseyin Bilgin. Email: 
Structural Durability & Health Monitoring https://doi.org/10.32604/sdhm.2025.071007
Received 29 July 2025; Accepted 03 September 2025; Published online 17 September 2025
Abstract
Nonlinear static procedures are widely adopted in structural engineering practice for seismic performance assessment due to their simplicity and computational efficiency. However, their reliability depends heavily on how the nonlinear behaviour of structural components is represented. The recent earthquakes in Albania (2019) and Türkiye (2023) have underscored the need for accurate assessment techniques, particularly for older reinforced concrete buildings with poor detailing. This study quantifies the discrepancies between default and user-defined component modelling in pushover analysis of pre-modern reinforced concrete structures, analysing two representative low- and mid-rise reinforced concrete frame buildings. The lumped plasticity approach incorporates moment-rotation relationships derived from actual member properties and reinforcement configurations, while the distributed plasticity approach uses software-generated default properties based on modern codes. Results show that the distributed plasticity models systematically overestimate both the strength and the deformation capacity by up to 35% compared to lumped plasticity models, especially in buildings with poor detailing and low concrete strength. These findings demonstrate that default software procedures, widely used in practice but not validated for pre-modern structures, produce dangerously unconservative seismic performance estimates. The study provides quantitative evidence of the critical need for tailored modelling strategies that reflect the actual conditions of the existing building stock.
Graphical Abstract
Keywords
Reinforced concrete frames; seismic assessment; pushover analysis; lumped plasticity; distributed plasticity
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