5306 Middle Fiskville Rd.
Austin, Tx., 78751
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Seismic Analysis and
Does your bridge satisfy the current structural
Sefbo Technology, Inc. recognizes that many existing
structures and most new bridge structures require earthquake design to safeguard against
structural failures and to limit damage, particularly if they are located in earthquake
zones 3 and 4. What makes seismic analysis unique and difficult for suspension bridges is
that in addition to the combinations of other structural components such as steel towers,
pipeline supports and concrete foundations one must also determine the dynamic response of
the cable system. Most engineers and studies do not contemplate the response
of a cable. At Sefbo our engineers not only can create a bridge that will resist the
effects of contemplated seismic ground motions, they also strive to produce economic
Dynamic Analysis Preferably,
all structures require some dynamic analyses procedures, which necessitate the appropriate
ground motion representation. Sefbo engineers create a mathematical model to represent the
physical structure, which shows the spatial distribution of the mass and stiffness of the
structure to the extent necessary to perform adequate calculation.
Equivalent Lateral Forces A
bridge can be engineered and constructed for ground motion producing structural response
and seismic forces in any horizontal direction. By using static force procedure,
determining seismic factors, understanding the vertical and horizontal distribution, the
impact of overturning, drift, and story limitation the proper design, theoretically, can
be achieved. However, this method quite often yields a product that is to conservative to
be cost effective.
Modal Superposition A
simplified structural model with lumped mass is used to create the structural model. This
method may work for a smaller bridge but does not yield enough information for longer or
more complex crossings.
Design Response Spectrum Analysis
This is a form of elastic dynamic analysis using the peak dynamic response of all
significant modes to determine the structural response. It is a representation of the
design basis ground motion, based on certain geological, tectonic, seismological and soil
characteristics associated with a specific site. From this Sefbo engineers can usually
determine the dynamic effects of an earthquake upon certain aspects of the bridge
Time-History Analysis This is
an analysis of the dynamic response of a structure when the base is subjected to a
specific ground motion time history.
Non-Linear Time-History Analysis
When time history is not available, a very detailed and thorough analysis of the
lateral force system must be reviewed. Capacities and characteristics of the nonlinear
elements shall be modeled with test data or substantiated analysis taking into
consideration many factors.
The basis for design and seismic retrofit depend on the
seismic zoning, the site characteristics, configuration and structural system and height
of a particular bridge. Our seismic design meets Uniform Building Code (UBC) requirements.