Improved Seismic Monitoring - Improved Decision-Making Assessing the Value of Reduced Uncertainty (2006) / Chapter Skim
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6 Benefits from Performance-Based Engineering
6 Benefits from Performance-Based Engineering
Pages 116-131
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From page 116... ...
Over the past 50 years, these observations have been aided significantly by the availability of seismic monitoring data -- records of earthquake events recorded by weak and strong motion instruments. All components of the built environment -- buildings, bridges, roads, utility networks, and dams -- share in the benefits of seismic monitoring, even though significant differences exist in how earthquake engineering is approached for each one.
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From page 117... ...
The relatively modest funding required for significantly improving seismic monitoring and the subsequent development of new seismic mitigation techniques should be viewed in light of the potential for reducing the cost of constructing new facilities, strengthening existing structures to achieve proper performance, and avoiding losses after major damaging events. The roughly $200 million investment required for improved seismic monitoring and the cost of continuing research using the records should be viewed in light of the more than $800 billion invested annually in construction, the $17.5 trillion value of the built environment in the United States (FEMA, 2004)
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From page 118... ...
Seismic monitoring has led to development of national seismic hazard maps that are used to design structures with appropriate strength and durability. Although engineers once suggested -- after the 1906 San Francisco earthquake -- that the entire nation shared a common threat from earthquakes, it is now understood that the seismic hazard varies dramati 1A design-level earthquake represents the strongest ground motion expected to occur with a specified exceedence probability during the life of a building.
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From page 119... ...
Earthquake engineering design techniques have improved after each damaging earthquake and resulted in increasingly more advanced seismic design standards. When an earthquake occurs and structures experience more damage than their owners and engineers judge acceptable, the community of engineers adjusts design standards to avoid a repeat occurrence.
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From page 120... ...
In order to adequately initiate the development of the next generation of design procedures to achieve the goals of earthquake engineering, specific recorded information is needed for a variety of construction styles and geologic conditions. After the 1971 San Fernando earthquake, seismic monitoring programs at federal and state levels were expanded to begin to provide the needed information.
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From page 121... ...
Another example of the inadequacy of the current seismic monitoring programs resulted from the 2003 San Simeon earthquake. Because this was an area of only moderate seismicity, few ground motion instruments and a single building instrumentation package had been installed.
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From page 122... ...
Needed Improvements To achieve the benefits that improved seismic monitoring can potentially provide, the following six enhancements to the current monitoring program are needed: 1. The addition of sufficient free-field instruments nationwide to develop an understanding of the relationship between the source characteristics of an earthquake and the strong motions that are produced.
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From page 123... ...
Special emphasis should be placed on instrumenting publicly owned buildings, especially federal buildings, to ensure continuity of maintenance of the instruments, open access to information about structural design and construction history, timely access to the monitoring records and to the buildings themselves so that recorded shaking levels can be correlated to actual building damage, and avoidance of liability issues that may concern private building owners.
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From page 124... ...
This will allow a full understanding of the source and impact of element failures in the system that will lead to more robust designs. CALCULATION OF BENEFITS PROVIDED BY PERFORMANCE-BASED ENGINEERING When assessing the value of improved seismic monitoring as it relates to performance-based engineering, three parameters must be considered.
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From page 125... ...
The second is the implementation of the initial phase of the ANSS program, and the final step would be to add sufficient seismic monitoring nationwide to ensure that every damaging earthquake that occurred would be recorded to the extent necessary to advance the engineering design standards as much as possible. If these proposed enhancements are not done, the existing networks will continue to deteriorate due to age and obsolete technology, and eventually little seismic monitoring will exist to capture data from future 4An approximate annualized value is derived by multiplying the dollar value of the capital stock by a plausible long-term interest rate, estimated as 4 percent.
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From page 126... ...
The U.S. Geological Survey (USGS)
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From page 127... ...
Even with these limitations, these maps have refined our understanding of the nationwide distribution of earthquake hazards. Improved seismic monitoring using adequate free-field instruments is a critical requirement for further refining these maps.
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From page 128... ...
5. Improved procedures for new construction: Improved seismic monitoring will provide the records needed to calibrate the earthquake engineering process, remove conservatism as appropriate, and reduce the cost of construction.
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From page 129... ...
6. Improved procedures for rehabilitation of existing construction: From the decision to consider seismic hazards, to the process for identifying the seismic deficiencies in a building, to the actual techniques for rehabilitating buildings, improved seismic monitoring will enhance understanding, reduce conservatism as appropriate, and make seismic mitigation more affordable and acceptable.
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From page 130... ...
130 FEMA FEMA FEMA FEMA owner owner, owner owner, owner, owner, truction. Beneficiary Building Building Building Building Building Building cons Monitoring initial million million million million million million million or Seismic Annual Savings $3 $2 $49 $34 $20 $34 $142 Saved million million million million rehabilitation, Improved Rehabilitation Cost $75 $63 $850 $850 from repair, during a million million Benefits billion billion billion Seismic Cost $150 $315 $4.9 $34 $34 building a to billion billion billion billion Construction billion billion rehabilitate.
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From page 131... ...
BENEFITS FROM PERFORMANCE-BASED ENGINEERING 131 SUMMARY This discussion has been rooted in observation and experience in the design and construction environment. It has attempted to generalize the issues sufficiently to allow simple estimates to be made that subjectively quantify the value of improved seismic monitoring.
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