The occurrence of a large earthquake near a major city may be a rare event but its societal and economic impact can be so devastating that it is a matter of national interest. The earthquake disasters at Los Angeles, USA, in 1994 (61 fatalities and 30 billion US dollars); Kobe, Japan, in 1995 (over 6,400 fatalities and 100 billion US dollars); Kocaeli, Turkey, in 1999 (over 15,000 fatalities and 20 billion US dollars); Athens, Greece, in 1999 (143 fatalities and 2 billion US dollars); and Taiwan in 1999 (over 2,300 fatalities and 9 billion US dollars) are recent examples. Although seismic activity varies depending on coastal regions as reflected in the zones shown in Fig. 1.1, earthquake disasters have repeatedly occurred not only in the seismically active regions in the world but also in areas within low seismicity regions, such as in regions lor 2 in the figure. Mitigating the outcome of earthquake disasters is a matter of worldwide interest.
In order to mitigate hazards and losses due to earthquakes, seismic design methodologies have been developed and implemented in design practice in many regions since the early twentieth century, often in the form of codes and standards. Most of these methodologies are based on a force-balance approach, in which structures are designed to resist a prescribed level of seismic force specified as a fraction of gravity. These methodologies have contributed to the acceptable seismic performance of port structures, particularly when the earthquake motions are more or less within the prescribed design level. Earthquake disasters, however, have continued to occur. These disasters are caused either by strong earthquake motions, often in the near field of seismic source areas, or by moderate earthquake motions in the regions where the damage due to ground failures has not been anticipated or considered in the seismic design.
The objectives of the seismic design guidelines for port structures presented in this report are to address the limitations present in conventional design, and establish the framework for a new design approach. In particular, the guidelines are intended to be :
performance-based, allowing a certain degree of damage depending on the specific functions and response characteristics of a port structure and probability of earthquake occurrence in the region,
user-friendly, offering design engineers a choice of analysis methods, which range from simple to sophisticated, for evaluating the seismic performance of structures, and
general enough to be useful throughout the world, where the required functions of port structures, economic and social environment, and seismic activities may differ from region to region.
The expected users of the guidelines are design engineers, port authorities, and specialists in earthquake engineering. The applicability of the guidelines will reflect regional standards of practice. If a region has no seismic codes or standards for designing port structures, the guidelines may be used as a basis to develop a new seismic design methodology, or codes applicable to that particular region. If a region has already developed seismic codes, standards, or established design practice, then the guidelines may be used to supplement these design and analysis procedures. It is not the intent of the authors to claim that these guidelines should be used instead of the existing codes or standards or established design practice in the region of interest. It is anticipated, however, that the guidelines will, with continual modification and upgrading, be recognized as a new and useful basis for mitigating seismic disasters in port areas. It is hoped that the guidelines may eventually be accepted worldwide as recommended seismic design provisions.
Earthquake engineering demands background knowledge in several disciplines. Although this background knowledge is not a pre-requisite to understanding the guidelines, readers may find it useful to have reference textbooks readily available. Pertinent examples include Kramer (1996) on geotechnical earthquake engineering and Tsinker (1997) on design practice for port structures.
This summary report provides an overview of the seismic design guidelines. The complete guidelines document will be available in a book published separately through Balkema in 2001. Highlights of the book Seismic Design Guidelines for Port Structures"" will include the following Technical Commentaries (TC) :
- TC1: Existing Codes and Guidelines
- TC2: Case Histories
- TC3: Earthquake Motion
- TC4: Geotechnical Characterization
- TC5: Structural Design Aspects of Pile-Deck Systems
- TC6: Remediation of Liquefiable Soils
- TC7: Analysis Methods
- TC8: Examples of Seismic Perfonnance Evaluations