Uprooting collapse mechanism of RC structures in earthquakes

The Kahramanmaraş Earthquake Sequence of February 6, 2023, stands as the deadliest earthquake in Turkey during the era of instrumental seismology. A significant factor in this tragedy is the large building stock of Turkey, comprised of reinforced concrete (RC) buildings, many of which are vulnerable attributing to the widespread destruction. The weaknesses in the Turkish RC building stock have been well-documented, as they have repeatedly manifested in past earthquakes. However, given the progress in seismic codes and hazard maps over the past two decades, greatly advanced because of the 1999 earthquake, the widespread collapse of buildings constructed after 2000 was largely unexpected. This paper focuses on a specific type of collapse mechanism repeatedly observed during post-earthquake reconnaissance missions. Termed here as the “uprooting collapse”, this mechanism differs from the more common pancake-style collapses typically seen in substandard Turkish RC buildings. The possible causes behind the uprooting collapse are explored using an actual case study from the earthquake zone, supported by parametric analyses on RC frame buildings designed in accordance with the Turkish Seismic Code. The results indicate that when specific conditions align, such as high velocity demands, flexible load-bearing systems, improper structural member design, and a high height-to-width ratio, a total collapse in an uprooting fashion becomes possible even if construction quality standards and design code requirements are met.