Influence of high sustained axial stresses on the seismic behavior of full-scale substandard reinforced concrete columns

Reinforced concrete (RC) columns are critical structural components that play a decisive role in the seismic performance of buildings. However, the combined effects of long-term sustained axial loads and seismic loading on these columns remain a pressing concern. In particular, design and construction deficiencies, coupled with material deterioration, often result in substandard RC columns experiencing long term axial stresses that far exceed typical service levels. These elevated stress conditions can lead to significant structural vulnerabilities, manifesting as collapses under seismic actions or even under gravity loads alone. Within this context, this study aims to investigate the impact of such high sustained axial stresses on the response of substandard reinforced concrete columns prior to be subjected to reversed cyclic lateral loading simulating seismic actions. For this purpose, two full-scale columns were tested under the combined actions of axial load and reversed cyclic lateral displacements. One of two columns were tested after it was exposed to a sustained axial load of 825 kN, corresponding to 70% of axial load capacity (fbh) for a duration of six months, while the other column was tested as the reference specimen right after it was subjected to same level of axial load. Comprehensive instrumentation during testing and detailed creep analysis under long-term applied axial loads were conducted to evaluate the response of the columns. The findings highlight the significant impact of long-term high axial stress on the seismic performance of substandard RC columns.