Is an Earthquake-Damaged Building Safe to Use?
A major earthquake will damage hundreds, maybe thousands, of buildings all at once. As people recover from the shock, they will need to know quickly which buildings are safe to use and which are not. Can they live in their homes? Can the hospital stay open if it needs repair? Can the schools function?
Bhutan’s government asked GHI to develop a manual that will guide engineers who make such decisions. The goal is to improve safety and speed recoveryafter a disaster. Atop the Himalaya, Bhutan faces a high risk of earthquakes.
An earthquake-damaged traditional rammed earth home in Bhutan. GHI’s work will guide engineers’ safety evaluations of local building types. PHOTO: KARMA DOMA TSHERING
Using this tool, trained engineers will know what to look for as they evaluate which buildings might suffer additional, life-threatening damage in an aftershock as intense as the mainshock. They will post a red, yellow or greencolored placard on each building to inform the public. Green means “Inspected” and the building is usable; it may be unscathed or need small repairs. Yellow means “Restricted Use”; a part of the building is unsafe (such as near a masonry chimney), or access is limited. Red means “Unsafe” until repaired or demolished.
An earthquake-damaged traditional rammed earth home in Bhutan. GHI’s work will guide engineers’ safety evaluations of local building types. PHOTO: Department of Disaster Management, Royal Government of Bhutan
GHI worked with Bhutan’s Departments of Disaster Management and Engineering Services and the Applied Technology Council (ATC) to adapt the ATC-20-1 Field manual: Postearthquake safety evaluation of buildings for Bhutan’s context. ATC’s rigorous process is the only standard used in the U.S. and has been applied to evaluate building safety after every significant earthquake since 1989. Bhutan’s manual is the first adaptation of ATC-20-1 with ATC’s consent and full participation.
The majority of buildings in Bhutan are traditional rammed earth, stone masonry, and adobe construction—quite different from the US building stock. Some have vernacular timber-based systems. Bhutan considers its traditional architecture a cultural treasure. Though beautiful, the buildings have vulnerabilities. Damage from moderate earthquakes in 2009 and 2011 indicates that stronger shaking will cause significant damage, especially in rammed earth and stone buildings.
In the adapted field manual, our team added several new chapters to cover buildings found in Bhutan but not in the US. We also added more detailed graphics, with examples of crack types and sizes in masonry. A panel of Bhutan and US engineers provided extensive input and field research. The new manual provides many images of “Unsafe” and “Restricted Use” conditions as well as acceptable damage in the “Inspected” category, to prevent overly conservative evaluations. Rammed earth buildings in particular can suffer impressive looking cracks but not require an “Unsafe” posting.
Engineers may assess thousands of buildings in the critical first week after an earthquake. They will check roof and floor framing, columns, walls, diaphragms, and foundations. The ATC-20-1 field manual, ready-to-go for Bhutan, will save precious time. Its use will support consistent evaluations that occupants can trust.
Planning for efficient recovery is one way to manage known risk. This complements GHI’s earlier work to help Bhutan develop pre-earthquake vulnerability assessments, in which engineers identify building weaknesses. Bhutan’s government can also feed data on the extent of damages and usable buildings into its new Bhutan Disaster Assessment tool, to plan rebuilding. The field manual, though specific to Bhutan, provides an excellent model for post-earthquake safety evaluations in nations with similar building types. World Bank’s Global Facility for Disaster Reduction and Recovery (GFDRR) and the ATC Endowment Fund funded adaption of the ATC-20-1 field manual for Bhutan.