College of Science & Engineering Alumni Newsletter
Spring
2001
Innovative Seismic Engineering Design
By Wenshen
Pong, Ph.D., P.E.; SFSU School of Engineering
Many
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.