A few days after the massive explosion of August 4, 2020 at the port of Beirut in Lebanon, researchers were on the ground to map the impacts of the explosion in the port and the surrounding city.
The goal was to document and preserve data on structural and facade damage prior to reconstruction, said Jonathan Stewart, a civil and environmental engineer at the University of California, Los Angeles, who spoke about the effort during the 2021 annual meeting of the Seismological Society of America (SSA).
This effort also made it possible to compare the satellite surveys of NASA’s Jet Propulsion Laboratory on the effects of the explosion with data collected from ground surveys. Stewart and his colleagues concluded that satellite-based Damage Proxy Maps were effective in identifying severely damaged buildings and buildings in good condition, but were less effective in assessing intermediate levels of structural or facade damage.
“The main result is that the Damage Proxy Maps can definitely distinguish severe damage from lack of damage” for structural and facade ratings, said Stewart, “but they are not as good for finer tuning. “
“If what interests you is a fairly detailed picture of what happened, it is not able to replace a person who actually knows what they are doing looking at the structure, especially from the inside.” , he added.
The recognition of the Beirut explosion was organized by the National Science Foundation, sponsored by the Geotechnical Extreme Events Reconnaissance Association (GEER). In addition to Stewart and his colleagues at the American University of Beirut, the team included members from the University of Illinois and the University of Calabria in Italy. The information analyzed by the GEER team can help engineers learn more about how to build safely against similar destructive events, including earthquakes, in the future.
Their findings, detailed in a GEER report, “also make recommendations on how you can optimize human resources during these inspections,” said Stewart.
That August day, a fire in the port detonated about 2.75 kilotons of TNT equivalent of ammonium nitrate and fuel, an event the size of a magnitude 3.3 earthquake. Within days, engineers at the American University of Beirut “had set up a hotline where those concerned with the stability of damaged structures could call,” said Stewart.
Professors and students have made visits to inspect and assess the stability of these and other structures, but in-person visits were reduced in September due to COVID-19. After that, the researchers relied on street view surveys, using 360-degree GoPro cameras mounted on cars driving around the city.
The damage was classified using scales adapted from those used for post-earthquake events, Stewart said. For example, structural damage has been rated on a scale starting from minor damage to non-loadbearing elements until the complete collapse of a structure. The damage to the facades was graded using a ladder that begins with cracked windows and continues until the windows and doors completely shattered.
The spatial patterns of damage caused by an explosion differ from those observed during an earthquake. Site conditions such as the underlying soil matter much more when it comes to the structural impact of an earthquake, while the damage caused by the explosion depends on “the severity of that explosion” , Stewart explained. “With an explosion, the damage decreases with distance and the number of buildings between you and the explosion that can deflect its effects.”
Stewart is not an expert in explosion seismology, but has experience in assessing structural damage after earthquakes through his work in post-earthquake areas with GEER. He contacted a colleague at the American University of Beirut after the disaster to offer his help in collecting observations that could be useful to future researchers and engineers.
“We felt it was important to collect perishable data that we believe will be useful for people studying the effects of urban explosions, and to learn something from this disaster to improve our resilience in the face of such explosions. future disasters, ”he said.