Seismic Risk Assessment of Reinforced Concrete Frame Structures in by avl14509


									  Seismic Risk Assessment of Reinforced Concrete Frame Structures in
   Southern California due to a Magnitude 7.8 Earthquake on the San
                             Andreas Fault
Authors: Kathryn Lynch, Kristen Rowe, Abbie Liel

        Due to the seismic nature and economic significance of the Los Angeles
region, it is important to evaluate the safety of structures in the area due to the next
big earthquake. This paper predicts damage and collapses possible in reinforced
concrete (RC) frame structures in Southern California due to the fictitious
magnitude 7.8 ShakeOut earthquake on the San Andreas Fault. The ShakeOut
project predicted ground motions for seven hundred sites spaced at ten-kilometer
intervals throughout the southern California region, which are used to evaluate the
impact of the ShakeOut scenario on RC structures.
        In order to obtain an accurate profile of structural response, both older and
modern RC commercial buildings are analyzed. This study assesses 20 RC moment
frame concrete office buildings typical of those found in California. These include 8
older RC buildings (constructed pre-1970) and 12 modern code-conforming special
moment frame structures. These buildings vary in height from 1 to 20 stories and
include both space and perimeter frame systems. The pre-1970 RC designs are
designed based on the 1967 Uniform Building Code specifications and are
representative of existing nonductile RC frame buildings. The modern structures
meet the requirements of the 2003 International Building Code, ASCE 7-05 and
ACI318-02. Since all of southern California is considered in zone 3 from the 1967
UBC, these older RC structures’ design remains constant throughout the sites.
However, the modern buildings are modified for the modern site-specific design
requirements in order to present more realistic results.
        The models utilize performance-based earthquake engineering methods and
nonlinear dynamic analysis to assess engineering demands, i.e. story drifts and floor
acceleration at each site. Since the analysis utilizes robust models capable of
capturing the strength and stiffness deterioration as a structure collapses under
seismic loads, collapse may be predicted at sites where ground motions are very
large. Each building model is implemented in the OpenSees analysis platform, with
each structure modeled in 2D and including both lateral and gravity systems.
        With the comparison of damage incurred to structures between existing and
modern structures, the increased seismic resistance of contemporary buildings is
demonstrated. Older, non-ductile RC frame buildings have been consistently
identified as being particularly vulnerable to significant damage and earthquake-
induced collapse, and in this study we can see how this would be borne out by a
particular southern California earthquake scenario. The outcome of the ShakeOut
presents an examination of the future risks and causalities of both life and property
in the next big earthquake, which will help with both seismic risk mitigation and
emergency response strategies. Results representing seismic risk and damage will
be represented using GIS software to graphically show how damage in modern and
older RC frames is predicted to vary over the greater Los Angeles region. This can
be used to identify particular buildings, types of buildings or regions that may be
particularly vulnerable in future earthquakes.

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