Soft-story and non-ductile concrete buildings are vulnerable to earthquake damage
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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
VERT Report, released January 23, 2021 Page 1/7
January 15, 2021 Mamuju-Majene Earthquake
Sulawesi, Indonesia
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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January 15, 2021 Mamuju-Majene Earthquake
Sulawesi, Indonesia
(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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January 15, 2021 Mamuju-Majene Earthquake
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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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January 15, 2021 Mamuju-Majene Earthquake
Sulawesi, Indonesia
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:
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