2:30 PM - 2:45 PM
[O10-03] How seismic design of infrastructure has evolved after the Great Hanshin Awaji Earthquake
★Invited Papers
Keywords:Level 2 ground motion, Anti-catastrophe, Performance-based design
The extensive damage caused by the Great Hanshin Earthquake had a major impact on the seismic design. The approach to the seismic design of various infrastructures changed significantly.
Prior to the Great Hanshin Earthquake, the 1980 Seismic Design Method etc. led to the introduction of Ductility Design Method in the 1990 Highway Design Specifications, which considered the ductility of structures after damage, assuming a design seismic motion of 1G class. With regard to seismic force, the standard value for the design seismic intensity was set at 1, and the yield strength was reduced based on the law of constant energy, allowing for damage due to large seismic motion and quantitatively evaluating the seismic resistance of structures.
One of the things that changed significantly after the Great Hanshin-Awaji Earthquake was the consideration of “L2 (Level 2) ground motion”, which was also mentioned in the JSCE seismic design standard for civil engineering structures. The classification of L1 ground motion and L2 ground motion as large ground motion of 1G class became clear after the Great Hanshin-Awaji Earthquake.
The earthquake recorded at the Kobe Meteorological Observatory had a maximum acceleration of over 800 gal. It was also characterized by the inclusion of large tremors such as the so-called “killer pulse”, and the idea of using two types of earthquake was also introduced.
In order to take into account the characteristics of seismic motion, there has also been a shift from static design to design using dynamic analysis.
Synthesis of design ground motion has also become important. Following the Great Hanshin-Awaji Earthquake, strong-motion observation networks were developed. With the advance of seismic motion simulation methodology, seismic ground motion simulation considering fault and ground conditions has also come to be adopted, rather than just using “standard ground motions.”
From around 1999, performance-based design, which aims to achieve the required performance rather than focusing on structural specifications, also began to be adopted. In 2002 the MLIT published the “Fundamentals of Design for Civil Engineering and Architecture”, which defined the required performance, such as “safety”, “usability” and “repairability”.
By around 2010, this advanced seismic design had matured technologically and design guidelines were about to be implemented. Then the Tohoku Earthquake occurred in 2011. The tsunami damage caused by this earthquake was enormous, and the phrase “beyond expectations” became widely used. This calls for measures to be taken that take into account the restoration of structures and the impact on society, in order to avoid catastrophic situations arising when external forces exceeding those assumed in the design are applied.
The design of railway structure proposed specific design methods for anti-catastrophe in 2012. Although the Road Bridge Design Specifications do not explicitly mention “anti-catastrophe”, the method of designing collapse scenarios as a way of envisaging specific disaster conditions was used in the design of the Shin-Aso Bridge, which was damaged in the 2016 Kumamoto earthquake. In 2022, the concept of anti-catastrophe was introduced in the Guidelines for Seismic Retrofitting of Waterworks Facilities, which indicates that the concept is widely adopted.
Anti-catastrophe is a way to consider how to respond to the assumption that damage will occur, and it is robust in the existence of uncertainty in the evaluation of seismic force. It is also consistent with the concepts of resilience. However, because the specific required specifications are not explicitly given, there is difficulty to make expert judgments, considering factors such as recovery after the disaster, the impact on other infrastructure, and social impact. These have been taken for granted in the past for important structures, but it is important that they have been established as part of the design procedure.
Prior to the Great Hanshin Earthquake, the 1980 Seismic Design Method etc. led to the introduction of Ductility Design Method in the 1990 Highway Design Specifications, which considered the ductility of structures after damage, assuming a design seismic motion of 1G class. With regard to seismic force, the standard value for the design seismic intensity was set at 1, and the yield strength was reduced based on the law of constant energy, allowing for damage due to large seismic motion and quantitatively evaluating the seismic resistance of structures.
One of the things that changed significantly after the Great Hanshin-Awaji Earthquake was the consideration of “L2 (Level 2) ground motion”, which was also mentioned in the JSCE seismic design standard for civil engineering structures. The classification of L1 ground motion and L2 ground motion as large ground motion of 1G class became clear after the Great Hanshin-Awaji Earthquake.
The earthquake recorded at the Kobe Meteorological Observatory had a maximum acceleration of over 800 gal. It was also characterized by the inclusion of large tremors such as the so-called “killer pulse”, and the idea of using two types of earthquake was also introduced.
In order to take into account the characteristics of seismic motion, there has also been a shift from static design to design using dynamic analysis.
Synthesis of design ground motion has also become important. Following the Great Hanshin-Awaji Earthquake, strong-motion observation networks were developed. With the advance of seismic motion simulation methodology, seismic ground motion simulation considering fault and ground conditions has also come to be adopted, rather than just using “standard ground motions.”
From around 1999, performance-based design, which aims to achieve the required performance rather than focusing on structural specifications, also began to be adopted. In 2002 the MLIT published the “Fundamentals of Design for Civil Engineering and Architecture”, which defined the required performance, such as “safety”, “usability” and “repairability”.
By around 2010, this advanced seismic design had matured technologically and design guidelines were about to be implemented. Then the Tohoku Earthquake occurred in 2011. The tsunami damage caused by this earthquake was enormous, and the phrase “beyond expectations” became widely used. This calls for measures to be taken that take into account the restoration of structures and the impact on society, in order to avoid catastrophic situations arising when external forces exceeding those assumed in the design are applied.
The design of railway structure proposed specific design methods for anti-catastrophe in 2012. Although the Road Bridge Design Specifications do not explicitly mention “anti-catastrophe”, the method of designing collapse scenarios as a way of envisaging specific disaster conditions was used in the design of the Shin-Aso Bridge, which was damaged in the 2016 Kumamoto earthquake. In 2022, the concept of anti-catastrophe was introduced in the Guidelines for Seismic Retrofitting of Waterworks Facilities, which indicates that the concept is widely adopted.
Anti-catastrophe is a way to consider how to respond to the assumption that damage will occur, and it is robust in the existence of uncertainty in the evaluation of seismic force. It is also consistent with the concepts of resilience. However, because the specific required specifications are not explicitly given, there is difficulty to make expert judgments, considering factors such as recovery after the disaster, the impact on other infrastructure, and social impact. These have been taken for granted in the past for important structures, but it is important that they have been established as part of the design procedure.