Soft-story and non-ductile concrete buildings are vulnerable to earthquake damage An Earthquake Engineering Research Institute (EERI) report developed in response to: M6.2 Mamuju-Majene Earthquake, Sulawesi Indonesia
Authors: Yolanda Alberto, Erica Fischer, Manny Hakhamaneshi, Gah-Kai Leung, and Eduardo Miranda Release date: January 23, 2021
This is a report developed by EERI’s Virtual Earthquake Reconnaissance Team. This report is based on publicly available data published within one week of the events. The assessment provided in the report is performed by the judgment of the authors with limited access to ground-truthing.
Soft-story buildings and non-ductile concrete buildings are vulnerable to earthquake damage in the US. The January 15, 2021 M6.2 earthquake in Sulawesi, Indonesia demonstrated the vulnerability of these buildings to earthquakes. In the US, many of our buildings in high-seismic regions can be characterized as soft-story or non-ductile concrete buildings. This includes schools and hospitals.
Earthquake Summary On January 14, 2021 at 2:28am local time a M6.2 earthquake occurred on the west coast of Sulawesi island near Mamuju, Indonesia. The epicenter was about 6 km northeast of Majene with a recorded intensity of VIII (USGS, 2021). A smaller earthquake (M5.7) occurred in the same area the day before (January 14). This earthquake was caused as a result of slip along the Sunda and Banda Sea plates in a reverse faulting mechanism. The M6.2 earthquake was a shallow earthquake with the hypocenter at 18 km below the earth’s surface. The northern west coast of the island of Sulawesi was significantly damaged in 2018 due to the M7.5 Palu earthquake and tsunami.
Soft-story buildings and non-ductile concrete buildings Soft-story and non-ductile concrete buildings are common buildings throughout our cities that are located in high-seismic regions. A soft-story building is one where one level of the structure (usually the lowermost level) is significantly weaker than the stories above it (Samant et al., 2009). A non-ductile concrete building is one constructed without the relevant provisions required to ensure ductile behavior during a strong earthquake (Baradaran Shoraka et al., 2013). These buildings have significant vulnerabilities to catastrophic seismic damage that can cause casualties and fatalities. In the US and abroad, these types of buildings are used to construct all types of buildings including community hospitals and schools. According to the California Seismic Safety Commission, there are an estimated 40,000 non-ductile buildings throughout California alone (Seymour et al., 2009). Non-ductile buildings are also common in the Pacific Northwest, including densely populated areas such as Seattle and Portland, which also face major seismic hazards (Raghunandan et al., 2015). The San Fernando earthquake of 1971 caused significant hospital damage to the Olive View Medical Center (shown in Figure 1). This damage shed light on the implications of non- ductile concrete buildings and motivated changes in building codes for detailing concrete structures in high
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seismic regions. Samant et al. (2009) calculated that retrofitting non-ductile concrete buildings to minimal performance objectives in the state of California would save $24,000 per residential unit in a M7.2 earthquake, through avoided losses to structure and contents. These avoided losses increase to as much as $52,000 per residential unit if more substantial retrofitting is implemented (Samant et al., 2009).
Figure 1. Damage to the Olive View Medical Center in the 1971 San Fernando earthquake (photo per SEAONC, 2019)
Healthcare buildings Two hospitals in Mamuju were heavily damaged, both of which were non-ductile concrete buildings. The Mitra Manakarra Hospital in Mamuju collapsed causing eight casualties (BBC, 2021). About 60 people were safely evacuated from the hospital. Figure 2a shows the hospital before the earthquake and Figures 2b - d show the hospital after the earthquake. From the before and after photos of this hospital, it seems that this building collapsed due to poor detailing at the beam-column joints (Gunay et al., 2021). The second hospital that was damaged was the Mamuju District General Hospital (Figure 3). This hospital was three- stories and had large round columns in the front. Damage shown in Figure 3b consists of broken windows at the front of the hospital, partial collapse of the roof, and significant damage to the unreinforced masonry walls at the front of the building.
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(a) (b)
(c) (d) Figure 2. Mitra Manakarra Hospital in Mamuju (a) before the earthquake (photo from Google), (b) - (d) after the earthquake showing collapse of the building (ABS-CBN News, 2021; SBS, 2021; Getty Images 2021)
Figure 3. RSUD Kabupaten Mamuju Hospital (Mamuju District General Hospital) (a) before the earthquake (Gatra, 2020) (b) photo after the earthquake (USA Today, 2021)
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Educational buildings Schools in Indonesia have a long history of seismic vulnerability. After the 2009 Padang earthquake, 1,100 schools were damaged or collapsed (Build Change, 2021). Today, over 136,000 teachers and students remain at risk in schools. The Lombok earthquake, damaged over 600 educational buildings including 341 primary schools (Reliefweb, 2018). Schools provide a safe place for children to learn and play, which can help in the recovery process by dealing with the trauma that occurs due to a devastating earthquake. About 59 schools and 40 Islamic schools were damaged due to the 2021 Sulawesi earthquake (OCHA, 2021).
Summary of Local Building Codes Indonesia is one of the most disaster-prone regions of the world. Over the last 30 years, Indonesia has experienced about 289 disasters per year resulting in approximately 8,000 fatalities mainly due to falling masonry and collapsed buildings (OCHA, 2021). The first building codes in Indonesia were developed in 1998 and required by law to be adopted in 2002. A national seismic code was developed and adopted in 2012. In 2017, a seismic hazards model was developed by the Team for Updating Seismic Hazard Maps of Indonesia of the National Center for Earthquake Studies, Indonesia (Irsyam et al., 2017). The model was developed through international collaboration with entities such as the US Geological Survey (USGS) and Geoscience Australia. Schools in Indonesia have been studied by others to improve the construction practices within the country (Rogers, 2012; Blaisdell Collins and Triani N, 2019). These schools are often constructed as one- story partially-confined masonry buildings with very little reinforcement in the concrete frame. However, Indonesia’s building code does not address confined masonry even though the Ministry of Education promotes the use of this construction technique through their guidelines. It is common that the front and back walls have openings for windows and doors leaving very little wall to resist seismic demands. In addition, top beams are often left out of the construction thereby leaving the columns and the unreinforced masonry walls unbraced at the top. The roof of these school buildings are light-frame roofs that do not brace these elements in the out-of-plane directions. Work by Build Change and GeoHazards International has included working with local skilled laborers to teach them how to construct schools in a way that improves the seismic behavior of the school buildings.
Sheltering and emergency response According to the OCHA (2021) the National Agency for Disaster Management (BNPB) displaced more than 15,000 people to 15 evacuation sites a day after the earthquake. There were some looting incidents that made the police provide escort for delivery of goods, such as blankets, mats, tarpaulin, tents, medicines, masks, personal protection equipment (PPE) and ready-to-eat meals. As of January 16, BNPB assigned the International Disaster Response (IDR) four billion for emergency response: IDR two billion for the Government of West Sulawesi Province, and IDR one billion each for Mamuju and Majene (OCHA, 2021). The Indonesian National Army (TNI) launched two infantry, engineering companies aircrafts, tents, generators, excavators and trucks. The Ministry of Health organized a Rapid Health Assessment and Emergency Medical Teams, 25 ambulances, tents, medicines, PPE, and masks, among others.
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The Ministry of Social Affairs provided IDR 1.7 million ready-to-eat meals, food packages for children, tents, mattresses, blankets, kitchen kits, multipurpose tents, portable beds, clothing and personal kits (OCHA, 2021). In West Sulawesi, the police have motivated people and retail entrepreneurs to continue economic activities by also providing security against looting (BNPB, 2021).
What we can learn from this earthquake and apply to the US This earthquake highlights the need to improve the seismic performance of hospital and school buildings, not only in Indonesia but in all seismic regions in the world. On the west coast of the US, states have taken action to protect hospitals and school buildings. In the state of California, the Field Act was motivated by the 1933 Long Beach earthquake that destroyed or damaged over 230 school buildings. This piece of legislation was one of the first that mandated seismic forces to be considered in building construction. The Field Act requires that seismic forces be considered in the design of school buildings and established the Office of the State Architect, which provides oversight and quality control to the construction and design of public school buildings in the state of California. As a result of previous earthquakes, the state of California has also issued legislation to improve the seismic performance of hospitals. In particular, as a result of the February 9th, 1971 San Fernando earthquake in which several hospitals collapsed, the Alfred E. Alquist Hospital Facilities Seismic Safety Act was issued in 1983, which established a program of seismic safety building standards for hospitals constructed after 1973. As a result of the 1994 Northridge earthquake in which several earthquakes experienced extensive nonstructural damage and had to be evacuated, a new legislation, the Senate Bill 1953, established a seismic safety building standards program under California's Office of Statewide Health Planning and Development (OSHPD) with stricter requirements for hospitals built after 1973. Over 50% of California’s hospitals fall into this category. Similarly, the state of Oregon established the Seismic Rehabilitation Grant Program (SRGP), which is a program that provides funding (up to $1.5 million) to public schools, hospitals, and emergency services facilities (police and fire stations). Recently, the Bay Area and Southern California have passed an ordinance on soft-story wood structures and in Southern California an ordinance on non-ductile concrete buildings in an attempt to force building owners to perform seismic retrofits on these vulnerable buildings.
References: ABS-CBN News (2021, January 15). Powerful quake rocks Indonesia. https://news.abs- cbn.com/overseas/multimedia/photo/01/15/21/powerful-quake-rocks-indonesia
Baradaran Shoraka, M., Yang, T. Y., and Elwood, J. (2013) ‘Seismic loss estimation of non-ductile reinforced concrete buildings’, Earthquake Engineering and Structural Dynamics 42, pp. 297-310.
BBC News (2021, January 15). Indonesia earthquake: Dozens dead as search for survivors continues. https://www.bbc.com/news/world-asia-55672126
BBC News (2021, January 17). Indonesia earthquake: Heavy rain hampers search for survivors. https://www.bbc.com/news/world-asia-55696063
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Blaisdell, L.C., Mwangi, J.P., and Triani M.N., (2019). “Improving school buildings in Indonesia” https://www.structuremag.org/?p=14065
BNPB (2021). Post-earthquake in West Sulawesi, Kombes Pol Hemi: Don’t be affected by hoaxes. https://bnpb.go.id/berita/pascagempa-sulbar-kombes-pol-helmi-masyarakat-jangan-terpengaruh-hoaks
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Gatra (2020, March 18). Mamuju Hospital Prepares Corona Patient Isolation Room. https://www.gatra.com/detail/news/472424/kesehatan/rsud-mamuju-siapkan-ruang-isolasi-pasien-corona
Gunay, S., Hassan, W.M, Miranda, E., Robertson, I., and Wibowo, H. (2021). “15 January 2021, Mamuju-Majene Earthquake, West Sulawesi,” Structural Engineering Extreme Event Reconnaissance Team (StEER).
Irsyam, M., Widiyantoro, S., Natawidjaja, D., Meilano, I., Rudiyanto, A., Hidayati, S., Triyoso, W., Hanifa, N. R., Djarwadi, D., Faizal, L. Sunarjito (editor), Team for Updating of Seismic Hazard Maps of Indonesia 2017. 2017. Earthquake Source and Hazard Maps of Indonesia 2017. National Center for Earthquake Studies (PusGen), Research Center for Housing and Human Settlement, Directorate General for Research and Development, Ministry of Public Works and People Housing, ISBN 978-602-5489-01- 3. (in Indonesian)
OCHA (2021). INDONESIA: West Sulawesi Earthquake. Flash Update No. 2. As of 16 January 2021, https://reliefweb.int/sites/reliefweb.int/files/resources/Indonesia%20West%20Sulawesi%20Earthquake%2 0Flash%20Update%20%232.pdf
Reliefweb (2018, August 2018). Hundreds of schools damaged by earthquakes on Indonesian island of Lombok. https://reliefweb.int/report/indonesia/hundreds-schools-damaged-earthquakes-indonesian- island-lombok
Reliefweb (2021, January 16). Indonesia: West Sulawesi Earthquake Flash Update No. 2 https://reliefweb.int/report/indonesia/indonesia-west-sulawesi-earthquake-flash-update-no-2-16-january- 2021
Pribadi, K.S., Kusumastuti, D., and Rilodva (2008). “Learning from recent Indonesian earthquakes: an overview to improve structural performance.” The 14th World Conference on Earthquake Engineering, https://www.iitk.ac.in/nicee/wcee/article/14_01-1019.PDF
Raghunandan, M., Liel, A. B., and Luco, N. (2015) ‘Collapse Risk of Buildings in the Pacific Northwest due to Subduction Earthquakes’, Earthquake Spectra 31(4), pp. 2087-2115.
Samant, L. D., Porter, K., Cobeen, K., Tobin, L. T., Kornfield, L., Seligson, H., Alejandrino, S. and Kidd, J. (2009) ‘Mitigating San Francisco’s Soft-Story Building Problem’, in Goodno, B. (ed.) Proceedings of
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the 2009 ATC and SEI Conference on Improving the Seismic Performance of Buildings and Other Structures . San Francisco, CA: American Society of Civil Engineers.
SBS News (2021, January 17). Indonesian rescue crews search for survivors after earthquake that killed at least 73 people. https://www.sbs.com.au/news/indonesian-rescue-crews-search-for-survivors-after- earthquake-that-killed-at-least-73-people
SEAONC (2019). Olive View UCLA Medial Center, 1971 San Fernando Earthquake.
Seymour, E., Greene, M., Anagnos, T. and Comartin, C. (2009) ‘Inventory of Non-ductile Concrete Buildings in High Seismic Risk Areas of California’. Available at:
USA Today (2021, January 15). Deadly earthquake hits Indonesia’s Sulawesi island. https://www.usatoday.com/picture-gallery/news/world/2021/01/15/deadly-earthquake-hits-indonesias- sulawesi-island/4172065001/
USGS (2021). M 6.2 - 32 km S of Mamuju, Indonesia. https://earthquake.usgs.gov/earthquakes/eventpage/us7000d030/region-info
VOA News (2016, December 12). Education: a casualty of earthquake in Indonesia’s Aceh, Aid Agencies Say. https://www.voanews.com/east-asia/education-casualty-earthquake-indonesias-aceh-aid-agencies- say
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