Civil Engineering: Assessment of Building Seismic Retrofit Measures
Abstract: Following the Great Hanshin-Awaji Earthquake in 1995, the Japanese government enacted legislation aimed at encouraging earthquake-resistant upgrades for buildings. This study assesses the effectiveness, efficiency, administrative feasibility, and technological incentives associated with these policies. Data indicates that the goal of enhancing the seismic safety of existing buildings should be reached by 2018 if current improvement trends persist. While the national government supports retrofitting of school buildings through local governments and guidelines, challenges remain in ensuring safety for all structures. These include persuading elderly homeowners to invest in seismic upgrades and fostering awareness among property owners about the importance of prioritizing building safety. Local governments have initiated various efforts, such as community seminars, financial support programs, seismic assessments, and earthquake hazard mapping. Additionally, the paper offers suggestions for enhancing existing seismic retrofit policies, drawing insights from international experiences in building retrofits.
1. Background
Following the Great Hanshin-Awaji Earthquake in 1995, the Japanese government introduced approximately 20 legal frameworks, including the “Retrofit Promotion Act” established in 1995, to facilitate earthquake-resistant building retrofits. Additionally, numerous local governments in Japan began offering various support systems to encourage seismic retrofits undertaken by property owners and the private sector. The national government also implemented new subsidy programs such as regional housing grants and community renovation grants under the Retrofit Promotion Act. Furthermore, a tax reduction system for loans related to seismic retrofitting was initiated in the fiscal year 2006.
Why have so many public assistance systems been established for housing seismic retrofitting, even though houses are considered private assets? This question emerged shortly after the Great Hanshin-Awaji Earthquake. Was it a decision by the government to refrain from allocating tax revenue (public assistance) for individual house reconstruction?
One possible reason for this policy change could be traced to the introduction of the “Act concerning Support for Reconstructing Livelihoods of Disaster Victims” in 1998, with revisions in 2004. This legislation, enacted in response to various disasters following the Great Hanshin-Awaji Earthquake, allows for the provision of public assistance to owners of completely or partially destroyed houses, treating them as private assets. For example, owners of completely destroyed houses may receive one million yen for purchasing household items and two million yen for house reconstruction, totaling three million yen in grants.
Additionally, the collapse of houses during earthquakes often results in blocked streets, posing significant challenges to evacuation, firefighting, and relief efforts, as observed in the Great Kanto Earthquake of 1923 and in Nagata ward of Kobe city during the Great Hanshin-Awaji Earthquake. Thus, seismic retrofitting of buildings, including houses, is essential to ensure overall urban safety. Consequently, public assistance can be justified, even for privately-owned houses.
Considering estimates of potential casualties in the event of the Tokai Earthquake published by the Cabinet Secretary in 2005, it is projected that the maximum death toll could reach approximately 9,200 individuals in the event of an assumed ocean-type Tokai Earthquake. Of these, around 85%, roughly 7,900 deaths, would result from building collapses and similar incidents. Simultaneously, the Japanese Cabinet Secretary set a target to halve these casualties in the “Earthquake Disaster Mitigation Strategy” for the Tokai Earthquake. To achieve this, a specific goal was established to increase the housing seismic retrofitting ratio from the current 75% to 90% within ten years, by 2015. The “Earthquake Disaster Mitigation Strategy” was also formulated for the anticipated Tohnankai and Nankai (South-east Ocean and South Ocean) Earthquakes in 2005, with primary objectives focused on housing seismic retrofit and tsunami disaster prevention measures.
These circumstances prompted various actors to introduce new support measures for housing seismic retrofitting across Japan from the inception of the Strategy in 2005 to the present day.
2. Retrofit Systems in Japan
2.1 Technical Background
The devastating Great Hanshin-Awaji Earthquake in 1995 exposed vulnerabilities in reinforced concrete (RC) structures designed according to pre-1981 building codes. The primary issue with RC columns was their lack of lateral reinforcement. Enhancing their capacity for larger deformations involved methods such as:
(a) Jacketing RC columns with steel plates
(b) Wrapping RC columns with fiber-reinforced plastics (FRP)
Utilizing FRP sheets was advantageous due to their ease of construction and lightweight properties. Installing bracing structures like structural walls or steel braces proved effective in limiting structural deformation, thereby preventing the failure of brittle components.
When selecting retrofit measures, consideration should be given to the building’s occupancy. For instance, strengthening RC columns typically involves removing mortar and finishing materials (e.g., tiles) from the concrete surface, which generates noise, vibration, and dust, making it impossible for occupants to remain in the building.
Advanced technology, especially in hospitals for post-earthquake medical treatment, could reduce earthquake-induced forces by incorporating isolation devices at the base. Additionally, dampers or energy-dissipating devices can reduce structural response. After the 1995 Kobe earthquake, reports of foundation pile failures surfaced. In some cases, pile foundation failure was found to reduce the seismic input to the superstructure, limiting damage. However, the cost of investigating and repairing damaged foundations is high, and it’s generally preferable to provide foundations with greater resistance.
The need for retrofitting is closely tied to changes in building codes, particularly the seismic code. When the building code was revised in 2005, as depicted in Figure 1, there was limited demand for retrofitting old buildings if only a small portion of new constructions adhered to the new code. However, as a substantial portion of the building stock began to follow the new code, owners of existing buildings started considering retrofitting.
2.2 Retrofit Promotion Act and Its Support Systems
The Retrofit Promotion Act was enacted in 1995 immediately after the Great Hanshin-Awaji Earthquake, driven by the urgent need to enhance the safety of urban environments dominated by houses and buildings. Key aspects of this Act include:
- Imposing an obligation on owners to assess and retrofit buildings used by many people.
- - Exempting retroactive application of building codes, except for seismic-related codes, for approved retrofit work.
- - Providing guidance, advice, and instructions from the responsible governmental agency.
Buildings used by many people are defined as those with more than three stories and a floor area exceeding 1,000 square meters, used for specific purposes such as schools, hospitals, department stores, offices, shops, hotels, and elderly care facilities.
When the Retrofit Promotion Act was introduced, Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT) conducted a survey to assess the condition of houses and buildings in terms of compliance with seismic codes (specifically, the 1981 level of seismic safety). Table 1 displays the updated results of this survey, along with the target level of seismic code compliance, as shown in Figure 2.
The Act was established to promote retrofitting of houses and buildings. Consequently, besides regulatory measures, the national government also introduced economic measures, which are available only in local governments that established a “Plan for Retrofit Promotion.” Table 2 illustrates the number and percentage of local governments with such plans, while Table 3 shows the number and percentage of municipalities that have implemented subsidy systems for seismic assessment and retrofitting.
These tables reveal that even by 2009, a quarter (25%) of municipalities had implemented a subsidy system for condominiums to assess and evaluate earthquake vulnerability. Concerning detached houses, almost two-thirds of municipalities had introduced subsidy systems by 2009 for assessments, and nearly half of them offered financial support for retrofitting. Figures in Table 3 (in parentheses) indicate numbers and percentages as of April 2008. Within a single year, these percentages improved significantly due to policy measures. However, there were limitations to financial support for retrofitting, particularly in the case of condominiums and non-residential buildings.
The MLIT reported several policy measures contributing to these improvements:
(1) Development of municipal Retrofit Promotion Plans.
(2) Establishment of prefectural/municipal subsidy systems.
(3) Promotion of retrofitting for public buildings.
(4) Ensuring a sufficient number of engineers for assessment and retrofit.
(5) Utilizing tax incentives for business-use buildings.
(6) Creating seismic hazard maps.
(7) Promoting best practices for seismic assessment and retrofit.
(8) Implementing model projects for seismic safety in houses and buildings.
These measures encompass various aspects, including socio-economic, informational, technical, and institutional components, to promote seismic assessment and retrofit of buildings.
2.3 Retrofit of Schools in Japan
The Great Hanshin-Awaji Earthquake in 1995 resulted in significant damage to school buildings. According to a report from the Ministry of Education, Culture, Sports, Science & Technology (MEXT), approximately 4,500 educational facilities suffered structural or non-structural damage. Fortunately, there were no casualties due to damaged schools, as the earthquake occurred early in the morning when schools were mostly vacant. However, 390 schools served as evacuation shelters, accommodating around 180,000 displaced individuals.
Subsequent major earthquakes, such as the Niigata-Chuetsu Earthquake in October 2004 and the Iwate-Miyagi Nairiku Earthquake in June 2008, also resulted in damage to school buildings. Undamaged schools played a crucial role in accommodating evacuated people. Given these experiences, ensuring the safety of school students and the suitability of school facilities as evacuation shelters for local communities became imperative.
MEXT formulated policies for structural and non-structural retrofitting of school buildings, recognizing the vital roles of these buildings:
(1) Places for educating children
(2) Venues for cultural and sporting activities for local communities
(3) Evacuation shelters during major disasters
The Building Standard Law of Japan was revised in 1981, adopting new seismic-resistant design methods. According to this revision, buildings constructed using these methods would sustain no damage in middle-class earthquakes (about JMA 5 upper scale). They would also avoid casualties and severe collapse even in major earthquakes (about JMA 6 upper) (Table 4).
To evaluate the seismic capacity of existing school buildings, Japan uses the seismic capacity index of structure (Is), as regulated by the Retrofit Promotion Act. The law stipulates that a building has a low risk of collapsing if its “Is” exceeds 0.6. However, due to the critical importance of school buildings, MEXT recommends that the “Is” of school buildings should surpass 0.7 after retrofitting.
The “Is” (Seismic Capacity Index of Structure) is determined by the formula: Is = Eo × S × T, where:
- Eo represents the basic structural seismic capacity index, calculated based on strength index (C), ductility index (F), and story index (St): Eo = C × F × St
- - S is a reduction factor that modifies the Eo index based on structural balance in both plan and elevation.
- - T is a reduction factor that modifies the Eo index, graded by time-dependent deterioration.
A survey conducted by MEXT in April 2002 revealed that public school buildings had not undergone satisfactory retrofitting. Only 30% of buildings constructed based on pre-1981 Old Seismic Resistant Design had undergone seismic assessment or diagnosis. Approximately 45% of public -operators’ Meeting for the Survey and Study of the Promotion of Earthquake-Resistant School Buildings” in October 2002. The outcomes of this council’s discussions were submitted to MEXT in April 2003 in a report titled the “Promotion of Earthquake-Resistant School Buildings.” Based on this report, MEXT stipulated the “Guidelines for the Promotion of Earthquake-Resistant School Buildings” in July 2003.
Chapter 1 of these guidelines outlines the basic concept of “earthquake-resistant school buildings,” while Chapter 2 provides methods for devising earthquake-resistant promotion plans, considerations, and suggested methods for determining the urgency of earthquake resistance projects.
The fundamental principles highlighted in these guidelines are:
(1) Prioritizing earthquake-resistant measures for school buildings at high risk of collapse or severe damage.
(2) Prompt implementation of seismic resistance evaluations.
(3) Swift development of plans for promoting earthquake resistance.
(4) Disclosure of results from seismic resistance evaluations and earthquake resistance plans.
(5) Inspection and measures for the earthquake resistance of non-structural elements.
MEXT has been urging municipal governments, responsible for school buildings, to promote retrofitting based on these guidelines. Additionally, as shown in the figure, MEXT has established a subsidy system for public school buildings (Table 2). Following the Sichuan Earthquake in China in May 2008, MEXT increased the subsidy rate for vulnerable school buildings (Is < 0.3) from half to two-thirds in June 2008.
This subsidy system has been instrumental in implementing retrofitting for school buildings in Japan. The data illustrates the earthquake resistance status of public elementary and lower secondary schools in Japan as of April 1, 2008. Approximately 48,000 school buildings, or 38% of them, were found to lack adequate earthquake resistance or required further assessment. Among these, 10,000 buildings were estimated to be at high risk of collapse in expected large-scale earthquakes. A commitment was made to reinforce all these high-risk buildings within five years. Moreover, as mentioned earlier, the subsidy rate for vulnerable school buildings was increased in June 2008. To accelerate the five-year retrofitting program into four years, MEXT added an additional national fund (114 billion JPY) to the regular budget of fiscal 2008 (115 billion JPY, totaling 229 billion JPY) in the supplementary budget of the Japanese government in October 2008, as shown in Table 6.
Even though structural components of school buildings, such as columns, beams, and walls, were sufficiently retrofitted, the retrofitting of non-structural members, including ceiling materials, fixtures, and furniture, is equally important. In the event of a major earthquake, these non-structural elements may fall or topple, posing risks to children and evacuated individuals. Thus, retrofitting non-structural members of school buildings is of utmost significance.
To encourage municipalities to implement non-structural seismic retrofitting for school buildings, the National Institute for Educational Policy Research of Japan (NIER) published a reference book on this topic in December 2005. This reference book included case studies, such as the one mentioned earlier.
3. Issues of Retrofit Works
3.1 Technical Challenges
It’s essential to recognize that these mitigation measures can vary from one country to another due to differences in expected building performance (minimum required strength and acceptable damage). These variations stem from factors like:
(a) Varied seismic risk levels
(b) Diverse levels of tolerance to hazards
(c) Distinct economic backgrounds
(d) Varying stages of technical development in construction practices.
Most building codes worldwide explicitly or implicitly permit structural damage during strong earthquakes as long as it preserves life safety, given the historical occurrence of such damage. To understand the extent of heavy damage in major earthquakes, data collected by the Architectural Institute of Japan (AIJ) from cities affected by significant earthquakes, like Mexico City, Lazaro Cardenas, Baguio, Erzincan, and Kobe, was analyzed. In each city, a heavily damaged area was identified, and structural engineers and researchers assessed the damage levels of all buildings in that area.
From these damage statistics (Table 7 and Fig. 3), it becomes evident how crucial it is to identify the small percentage of buildings potentially vulnerable in future earthquakes. Therefore, a straightforward procedure that quickly assesses the vulnerability of all existing buildings in a region, taking only a few hours per building, is desirable. This procedure would “screen out” the majority of safe buildings. More detailed and sophisticated assessments, which might take a few weeks, can then focus on the buildings identified as vulnerable in the simple procedure.
Fig. 3 Damage distribution of Mexico City.
For instance, in a screening process, dimensions of columns and structural walls per floor area can be used to estimate lateral load resistance roughly. While lateral load strength alone doesn’t fully represent a building’s safety, it provides an initial idea of whether the structure has sufficient capacity to withstand earthquake forces by strength. Buildings identified as questionable in the simple procedure would undergo more advanced analysis.
The following technological advancements and applications are required for earthquake disaster mitigation from a construction perspective:
(a) Effective earthquake-resistant building codes for new construction
(b) Methods for assessing earthquake vulnerability of existing buildings
(c) Seismic strengthening technologies for vulnerable buildings
(d) Methods for evaluating seismic damage to buildings after an earthquake
(e) Techniques for repairing damage to enable immediate occupancy
(f) Methods for rehabilitating damaged buildings for permanent use.
3.2 Socio-Economic Challenges
An examination of the allocation of government resources, both financial and human, for pre-disaster and post-disaster programs reveals a greater commitment to recovery than disaster prevention. Typically, more resources are dedicated to post-disaster emergency operations. This holds true for the international community as well. Disaster prevention programs tend to receive less attention. However, it’s crucial to recognize that while emergency operations occur after a disaster, often after lives have already been lost, disaster prevention measures have the potential to save many more lives.
Shifting focus to seismic resistance and isolation technologies for high-rise buildings is a common trend, but minimal research is dedicated to conventional houses. Despite the fact that over 80% of the global building stock consists of non-engineered structures, which include wooden houses in Japan, these unsafe buildings, inhabited by people, often receive limited attention and research funding. Similarly, when comparing spending habits for new versus existing houses, individuals tend to allocate more funds to new construction and less for maintenance. Yet, improving the safety of existing houses has the potential to save many lives.
Cost reduction is another essential aspect. Achieving this goal can involve technological advancements, government subsidies, and training programs for masons and carpenters in available techniques.
Political commitment also plays a critical role. While many individual homeowners would invest in reinforcing their houses if they understood the need, not all of them will do so. Some individuals may not prioritize it, considering that everyone ultimately passes away. The probability of death from an earthquake, which has a 40 percent chance of occurring in every 30 years, might seem negligible to some. Just as many smokers continue smoking despite health warnings, not all individual house owners will prioritize reinforcing their houses. One of the key challenges lies in persuading the elderly, who may be reluctant to invest in improving their old houses. Another challenge is raising awareness among homeowners, particularly housewives, about the importance of and priority in improving the seismic safety of houses.
4. Retrofitting Examples Worldwide
In this section, we present four global examples of retrofitting projects. In addition to cases within Japan, the author has been involved in retrofitting projects in Nepal, Indonesia, Uzbekistan, and China through initiatives at the UNCRD Hyogo Office and the Building Research Institute (BRI).
4.1 Example 1 (Houses in Nepal)
Nepal faces various disaster risks due to both natural factors and human-induced causes. The country has experienced several major earthquakes, including the 1934 Bihar Earthquake, which registered 8.3 on the Richter scale, resulting in 4,300 fatalities and the destruction of 20% of all structures. Three earthquakes of similar magnitude occurred in Kathmandu Valley in the 19th century. In 1988, another earthquake claimed 709 lives. The United Nations Centre for Regional Development (UNCRD) conducted a training project in Nepal in 2007, with technical support from NSET, focusing on practical measures that could be applied at the household level.
4.2 Example 2 (Schools in Indonesia)
Twenty female members from target communities participated in the training. They learned about earthquake science, the importance of disaster risk reduction, and how to implement non-structural risk mitigation measures in their homes. This included securing items like refrigerators and shelves using brackets and props. After the initial training, follow-up evaluations revealed that 19 participants had implemented non-structural measures in their homes within one or two weeks. They accomplished this either independently (13 people), with male family members (16 people), or by hiring a handyman (1 person). Seventeen participants discussed the training with relatives and friends, while 15 participants demonstrated the safety measures they had implemented in their homes.
This case study highlights the effective use of a communication network among housewives to disseminate seismic safety measures for houses, especially the fixation of furniture.
Historically, earthquakes have revealed that the vulnerability of school buildings is significantly higher compared to other infrastructures. The UNCRD and the Center for Disaster Mitigation (CDM) of the Institute of Technology Bandung (ITB) conducted a collaborative project aimed at reducing the vulnerability of existing school buildings in the corridor of the School Earthquake Safety Initiative (SESI) project. Two school buildings, SD Cirateun Kulon II and SD Padasuka II, both in Bandung County, were chosen for this project due to their urgent need for improvement and severe earthquake-resistant deficiencies.
The project encompassed retrofitting and strengthening these school buildings and other activities to enhance earthquake preparedness in the school community. Before any structural work commenced, the locations and layouts of the buildings were examined to ensure their retrofitting feasibility. Structural investigations determined the type and quality of materials used and assessed the existing lateral resistance system. The retrofitting design was based on the identified structural deficiencies, considering factors such as the buildings’ lifespan, earthquake resistance capacity, function, retrofit strategy, and techniques. The retrofit strategy also factored in the continuation of normal function, material and skilled labor availability, upgrades for non-structural components, and overall costs.
The retrofitting project began with SD Cirateun Kulon II, which consisted of two buildings made of reinforced concrete (RC) frames and masonry walls, with four rooms in each building. Structural analyses were conducted based on the actual materials and structural components. Earthquake risks were introduced by applying loads based on potential seismic threats and local soil conditions. The analysis indicated that both buildings were susceptible to poor performance under seismic loads, necessitating retrofitting. Physical work was then carried out to enhance structural quality and reduce earthquake vulnerability.
Building I, which was of lower quality, was retrofitted by adding appropriate RC frames with mat footings and providing anchorage to connect walls with columns and beams. Building II, in better condition, was retrofitted using wire mesh to strengthen wall elements. Double tie beams were added adjacent to the existing ones to enhance the foundation system. Both structures received detailed work on roof truss systems, as well as repairs to non-structural elements like doors, windows, and ceilings. Additionally, cosmetic repairs and improvements to sanitary facilities were conducted for both buildings.
4.3 Example 3 (Schools in Uzbekistan)
Tashkent, the capital city of Uzbekistan, is home to over 360 schools, nearly 20% of which have varying levels of deficiencies. Preliminary seismic risk analysis for Tashkent has indicated that more than 25% of school buildings could be completely destroyed, and 30% could suffer heavy damage in the event of a design earthquake.
School buildings in Tashkent primarily fall into two construction systems: brick and reinforced concrete (RC) frame-panel structures, with a few buildings constructed using adobe bricks. Approximately 35% of school buildings were built before the 1966 Tashkent earthquake, which was designed for an intensity of 7 on the MSK scale. Since 1966, half of the school buildings have been constructed using assembled RC frames of IIS-04, which are known to have inherent weaknesses in seismic resistance. This construction type’s vulnerability was demonstrated in earthquakes like Spitak (1988) and Kairakkum (1985) and confirmed through engineering analyses of earthquake consequences.
Many school buildings in Tashkent are situated in areas. with unstable soils, making both brick-walled and frame-panel structures susceptible to damage. The survey revealed that typical structures used for school buildings in Tashkent can be categorized into three groups: mixed brickwork and RC or wood reinforcing frame structures from the 1940s, brickwork structures commonly used until the 1960s, and frame-panel structures widely used in modern construction.
In order to establish a practical and regionally relevant link to local professional practices in Central Asia, and to align with standard analysis procedures, characterization was made to be consistent with a previous study on the Risk Assessment of Tashkent City conducted as part of the IDNDR RADIUS project in the 1990s.
4.4 Example 4 (Buildings in China)
The Ministry of Housing and Urban-Rural Development of the People’s Republic of China (MOHURD) conducted extensive investigations following the Wenchuan Earthquake. Based on analysis and research, MOHURD developed the “Technical Guide for Appraisal and Strengthening of Earthquake-Affected Buildings” on July 23rd, 2008. Subsequently, on June 13th, 2008, they issued the “Seismic Technical Specification for Building Construction in Town and Village,” which was implemented on October 1st, 2008.
China’s “Standard for Classification of Seismic Protection of Building Constructions” GB50223–2008 was enacted on July 30th, 2008, amending the original GB50223–2004. Moreover, the “Code for Seismic Design of Buildings” GB50011–2008, which was put into effect on July 30th, 2008, was an amendment of the GB50011–2001 standard. The experiences gained from the Wenchuan earthquake informed these seismic construction standards and codes.
In response to these amendments, MOHURD adjusted certain seismic standards, with a particular emphasis on enhancing seismic standards for public buildings such as secondary and primary schools and hospitals. This expansion included retrofitting efforts. Additionally, MOHURD made amendments to design codes and criteria, focusing on specific seismic technologies.
To leverage Japan’s expertise in seismic building technology and enhance earthquake and hazard prevention capabilities in China, the Financing & Foreign Affairs Department of MOHURD and the Japan International Cooperation Agency (JICA) initiated the “China-Japan Seismic Training Program” on May 12th, 2009. This three-year program received full support from the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) of Japan.
The International Institute of Seismology and Earthquake Engineering (IISEE) of the Building Research Institute (BRI) in Tsukuba, Japan, served as the implementing agency for training in assessment, retrofitting, and seismic building design since 2009.
5. In conclusion
In response to the Great Hanshin-Awaji Earthquake in 1995, the Japanese government introduced legislation aimed at promoting seismic retrofitting of buildings. This paper assesses the effectiveness of policies associated with the Retrofit Promotion Act. The data presented indicates that the policy goal of enhancing the seismic safety of buildings, specifically aiming for 90% compliance with the 1981 seismic code, is expected to be met between 2015 and 2018 if current improvement trends persist. In the realm of school buildings, the national government supports retrofitting efforts undertaken by local governments, guided by established retrofitting guidelines.
However, there remain significant challenges in ensuring the safety of all residences. Two key hurdles include convincing elderly homeowners to invest in improving the seismic resilience of their older houses and prioritizing seismic safety among housewives.
Presently, Japanese local governments are taking various initiatives, such as conducting community seminars, establishing financial support programs, offering consultancy for seismic assessments, and creating earthquake hazard maps. This paper also offers insights for refining existing policies to promote seismic retrofitting, drawing from international experiences in house and building retrofitting. International case studies, like the one in Nepal highlighting the role of women in disseminating knowledge about seismic safety for non-structural elements of houses, can inform the development of effective Japanese policies for retrofit promotion.
Japan’s experiences in seismic retrofitting have the potential to contribute to disaster risk reduction in other earthquake-prone countries worldwide. The lessons learned from Kobe and experiences shared globally should be disseminated to address the challenges associated with promoting policies and actions related to seismic assessment and retrofitting.
