Prepare for disasters by integrating structural and nonstructural measures. DRM measures should account for two levels of hazard. Level 1 events are relatively frequent and produce major damage; level 2 events, the largest possible disasters, have an extremely low probability but produce a devastating impact. Every possible structural and nonstructural measure should be
employed to protect against level 2. Structural measures should be designed to protect people, property, and socioeconomic activities against level 1 and to mitigate damages at level 2.
Provide technical and fi nancial support for local governments. The central govern-ment plays a crucial role in reducing disaster risks across the country. The central govern-ment should encourage local governgovern-ments to promote structural measures by providing fi nancial support and guide them in meet-ing minimum requirements for structures by producing technical guidelines and manuals.
Also, the central government should provide the local governments with technical sup-port, such as conducting training for techni-cal staff in planning, design, operations, and maintenance.
Consider designs and improvements to enhance the resilience of structures and to pre-vent sudden and complete failure. Extraordi-nary external loads caused by earthquakes, fl oods, and other events should be considered in designing structures such as dams and dikes, which should be designed in such a way so that they will mitigate damage even when the hazard level exceeds their design levels. Their eff ectiveness in mitigating damage should be ensured even in the event of their technical failure.
Raise dike levels in a phased manner, consid-ering the country’s fi nancial and social condi-tions. Safety standards and structural design upgrades against level 2 events should refl ect the concentration of population and economic assets in the protected areas. Although it may not be possible to build dikes capable of with-standing level 2 disasters, appropriate and fea-sible targets for dike design safety should be identifi ed.
Assure reliable operation of key facilities dur-ing emergencies. The safe and reliable operation of infrastructure must be ensured in emer-gency situations. Structural measures such as fl oodgates cannot provide reliable protection if
they cannot be operated under extreme condi-tions, such as power failures and the absence of operators. Multiple layers of operation should be assured. A suffi cient number of qualifi ed operators should be available during disasters, but not necessarily onsite. Developing manuals and conducting regular drills are required dur-ing normal times. The danger to which opera-tors are exposed should be minimized.
NOTES
Prepared by Mikio Ishiwatari, World Bank, and Junko Sagara, CTI Engineering.
1. The two- level approach has already been adopted in the design of other key infrastructure, such as dams and fl ood- prevention dikes. Dams typically consider the maximum probable fl ood or a fl ood with a 10,000- year return period when designing structural safety, and a 100- to 200- year return period for fl ood- control operations. For fl ood- prevention dikes to protect some critical areas of Tokyo and other locations, the government has increased design standards beyond the norm of 100- to 200- year fl oods.
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The strong main shock of the Great East Japan Earthquake of March 11, 2011, caused little damage to buildings. Buildings designed under the current building code and those with base isolation fared well. However, seismic design guidelines for nonstructural members had not been considered ade-quately, which resulted in problems such as the collapse of ceiling panels. Soil liquefaction occurred in reclaimed coastal areas along Tokyo Bay and riverside areas. The key lessons of the event are that seismic- resistant building design prevents collapse of buildings and protects human lives, that retro-fi tting vulnerable buildings is essential to reduce damage, that seismic isolation functioned well, and that nonstructural building components can cause serious damage. When applying these lessons to developing countries, local technical and socioeconomic conditions should be taken into account.
Building code updates following major earthquakes
After every major earthquake, Japan’s national government and academic community carry out detailed surveys of building damage, and the building code is revised accordingly. Tech-nical recommendations are based on the most recent lessons. The Tokachi- oki earthquake in 1968 caused serious damage to reinforced con-crete (RC) buildings and inspired a major revi-sion of the building code in 1981. Until 1981, the building code required buildings to withstand a lateral force of 20 percent of the total weight of the building without damage to structural