In the last issue of Perspectives, we reported on Kajima's extensive involvement in early efforts to provide relief and restore vital infrastructure and services following the Hanshin (Kobe area) Earthquake. Wile Kajima continues to play an important role in ongoing reconstruction efforts, this article focuses on how the company is mobilizing its seismic engineering resources to assess the implications of Japan's most destructive earthquake in over 70 years.
Beginning just after the earthquake struck on January 17, Kajima staff carried out hundreds of site inspections and collected an enormous volume of disaster-related information. Such investigations were essential for high-priority efforts to provide emergency relief, restore vital infrastructure and assist customers in reestablishing normal operations. At the same time, the data compiled represent a valuable source for analytical purposes and future reference.
Just ten days after the disaster, Kajima released a preliminary "flash" report, which was soon followed by two more substantial documents containing detailed seismographic data, damage assessments, photos, analysis, etc. For Kajima - which devotes fully 60 percent of its R&D budget to seismic technology - the importance of properly assessing the consequences of the earthquake and responding to its implications cannot be exaggerated. Accordingly, the company has mobilized its full resources and expertise to tackle these challenges, creating a special task force under the leadership of Kajima's Chief Executive Advisor Dr. Takuji Kobori, a world-renowned expert on seismic engineering.
Assessing the Hanshin Earthquake
While it is still too early to draw definitive conclusions, certain general points are clear. It is reassuring that high-rise buildings constructed in accordance with standards introduced in 1981 proved sound. In fact, none of the approximately 200 such buildings completed by Kajima in the affected area suffered significant damage. In contrast, major damage was sustained by many older, two-story wooden residential buildings, while mid-rise structures, for which design and construction methods vary, presented a mixed picture. The considerable damage to major highways, rail lines, ports and other infrastructure calls for careful study, especially in light of the serious impact of emergency relief activities.
According to Dr. Kobori, a central question is whether the Hanshin Earthquake, considered a "once-in-a-century" temblor, should now serve as the basis for benchmarking seismic standards. One problem is that an earthquake of remote oceanic origin, for example offshore of Tokyo or Nagoya, would have much greater magnitude and very different characteristics than the land-based active fault-induced Hanshin Earthquake. Dr. Kobori stresses that while it is important to study why some structures failed, it is even more vital to understand why others were able to withstand such strong seismic shocks.
Economics of seismic protection
While the Hanshin Earthquake showed the effectiveness of best current earthquake protection technology, the extensive damage raises questions about the feasibility of introducing advanced seismic engineering on a widespread bases. It is estimated that installing rubber isolaters under a 5- to 10-story apartment house would add about 5 percent to construction costs, a figure that would decrease as demand grew. More sophisticated active vibration control systems for high-rise buildings, a field where Kajima is a world leader, add less than 5 percent to construction costs, depending on the size of the building. How much should be invested in widespread protection against once-in-a-century disasters? Or should alternative approaches, such as easily restorable structures and backup infrastructure, be investigated more thoroughly?
A more integrated approach to preparedness
Until now the primary emphasis has been protecting structures from the direct effects of earthquakes, but the severity of secondary damage from the Hanshin disaster - including serious disruption of emergency medical services - make clear that greater attention should be given to these factors. Kajima president Akira Miyazaki suggests that the general contractor should be an advocate for a broader perspective on preparedness: "It is our duty to actively make suggestions for improving the overall earthquake resistance of projects. We also need to expand cooperation with academic and government institutions in carrying out research not only in seismic construction and engineering but also in urban planning and disaster prevention. Based on the results of these efforts, we must advance ideas and technology that can contribute to better disaster preparedness and improved safety".
Dismantling and removal of damaged infrastructure was an urgent priority following the earthquake. Left: Weakened elevated portions of the Hanshin Expressway were shored up with additional support.
Railroads, vital lifelines of the community, sustained extensive damage.
    
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