College of Science & Engineering Alumni Newsletter
Innovative Seismic Engineering Design
By Wenshen Pong, Ph.D., P.E.; SFSU School of Engineering
damaging earthquakes cause tremendous loss of life and property around
the world every year. Examples of earthquakes that caused significant damage
in the last decade such as 1989 Loma Prieta, California, 1994 Northridge,
California, and 2001 Nisqually, Washington in the United States and 1995
Kobe, Japan, 1999 Turkey, 1999 Chi-Chi, Taiwan, and 2001 Bhuj, India. It
is our goal to learn from earthquakes to advance our engineering design
concepts and to enhance our seismic hazard mitigation efforts, since we
are living in one of the most earthquake prone area in the United States.
The most important seismic hazards include ground shaking, structural failure, soil liquefaction, landslides, and lifeline hazards. The ultimate goal of the earthquake engineer is to improve earthquake-resistant design, so that structures will be strong enough to sustain design-basis earthquakes. To further understand the structural dynamic responses during strong earthquakes requires significant collaboration involving engineering geologists, seismologists, ego-technical engineers, and structural engineers. The geological and seismological evaluation is significantly important for seismic hazard efforts. The current building code strongly acknowledges the importance of the site-specific investigation of the soil property and the potential hazards of the seismic activities near the construction site. This recognition has been mainly due to the observations of major structural damages from earthquakes in the past.
While conventional structural design has been evolved and still is utilized in many construction projects, many innovative engineering methods are gaining increasing attention. Among them, base isolation and passive control using energy dissipation devices are the most viable options for enhanced seismic performance. Conventional structural design strategy is to increase structural stiffness and/or structural strength for higher structural demand. Although structural isolation and energy dissipations may not be appropriate design option for most buildings, they could be the most applicable for buildings that need to meet enhanced structural performance, such as 911 emergency centers and government buildings or many high tech companies that can afford the special costs associated with the design fabrication, installation, and maintenance. Base isolation and energy dissipation systems are relatively new and sophisticated concepts
that require more extensive design and dynamic analysis than do most conventional design.
Another new design approach is performance-based design. The four building performance levels are Operational performance level, Immediate occupancy performance level, Life safety performance level and Collapse prevention performance level. The four earthquake hazard level are identified based on the ground motion applied that have the following probabilities of exceedance and corresponding return periods: such as, 50%/50 year (Return period of 72 years), 20%/50 year (Return period of 225 years), 10%/50 year (Return period of 475 years) and 2%/50 year (Return period of 2475 years). The performance-based design concept is that building performance level must be designed based on the corresponding earthquake hazard level. The goal is for engineers to be able to identify the structural response during various levels of design earthquakes. It helps all the involved parties to understand the structural performance and safety objectives under different earthquake hazard levels.
In summary, seismic mitigation can be attained through multi-hazard mitigation efforts through research, education, hazard assessment, construction, engineering and awareness. As civil engineering professionals, it is our responsibilities to advance design and construction techniques for enhanced earthquake-resistant buildings. Through continuing education, career advancement and volunteerism, we, as future civil engineers, can make a difference in our society through multi-hazard mitigation efforts.
Finally, our school’s curriculum that directly contribute to the training of structural engineering includes ENGR 309 Mechanics of Solids, ENGR 323 Structural Analysis, ENGR 425 Reinforced Concrete Structures, ENGR 426 Steel Structures, ENGR 430 Soil Mechanics, ENGR 431 Foundation Engineering, ENGR 439 Construction Engineering, ENGR 461 Mechanical and Structural Vibrations, ENGR 833 Principles of Earthquake Engineering, ENGR 836 Structural Design for Earthquakes, ENGR 837 Geotechnical Earthquake Engineering.
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