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Learning From Earthquakes: A Closer Look at Terracon's Earthquake Engineering Services

Most of us cannot identify with the loss of life of more than 65,000 individuals associated with the May earthquake in the Sichuan Province of China. After all, less than 200 people have died in the United States from earthquakes during the last 40 years due to our seismic design standards and construction practices progressing immensely since the 1960s.

The nearly 30 million people affected by the earthquake in China could be matched by a strong earthquake centered near an economic hub in the United States. Recent examples of strong earthquakes and their far-reaching impact on commerce include the 1994 Northridge, Calif., and 1995 Kobe, Japan, events. Direct economic losses from these two earthquakes exceeded $40 billion and $150 billion, respectively. The Port of Kobe in Japan, one of the largest container facilities in the world before the earthquake, will most likely never regain its stature.

The number of severely and moderately damaged buildings following the 1994 Northridge earthquake numbered 29,000. Despite the damage to occupied structures, there were relatively few deaths because U.S. building codes have been developed to minimize loss of life. With the building code objective of life safety achieved, business owners can turn their attention to the economic losses that result from the inability to access red-tagged structures, the downtime necessary to repair salvageable buildings, and the burden of rebuilding what must be demolished. This new objective requires a more scientifically oriented design approach that meets an owner’s expected building performance levels under different earthquake scenarios.

The engineering profession has responded to the need for enhanced prediction of building response by developing performance- based earthquake engineering (PBEE). The PBEE process allows the owner and design team to make intelligent and informed decisions based on life-cycle considerations rather than construction costs alone. The figure below shows an example of the relationship between building performance objectives and four scenario earthquakes adopted from the Vision 2000 document (SEAOC, 1995).

PBEE emphasizes accurate characterization and prediction that employs a higher level of technology than the code design process. PBEE principles have already been incorporated into the seismic performance objectives of highway bridges: preserve life safety and prevent bridge collapse during rare earthquakes and provide immediate post-earthquake serviceability of bridges with minimal damage during expected earthquakes. Future updates of the International Building Code will eventually adopt PBEE concepts, but an increasing number of owners will take advantage of the methodology before that time arrives.

The current task for engineers is to design and build better and more economical structures. Design approaches like PBEE allow business owners to evaluate the costs and benefits of earthquake protection for new and existing facilities that are based on sound judgment.