Bridge seismic retrofit measures considering subduction zone earthquakes.
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2015-07-01
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Abstract:Over the years, earthquakes have exposed the vulnerability of reinforced concrete structures under
seismic loads. The recent occurrence of highly devastating earthquakes near instrumented regions, e.g. 2010 Maule, Chile
and 2011 Tohoku, Japan, has demonstrated the catastrophic impact of such natural force upon reinforced concrete
structures. Research was conducted to investigate the effect of subduction zone earthquakes on structural damage. The
study suggests that large magnitude ground motions of long duration have the potential of significantly increasing the
number of inelastic excursions and consequently incur more extensive structural damage as compared to ground motions
with similar elastic spectral demands but of shorter duration. This increase in demand plays a crucial role in the Pacific
Northwest where a mega subduction zone earthquake is impending.
Typical reinforced concrete bridge bents constructed in the 1950 to mid-1970 in the State of Oregon were designed and
built with minimum seismic considerations. This resulted in inadequate detailing within plastic hinge zones, leaving
numerous RC bents highly susceptible to damage following an earthquake. In this study, the cyclic performance of an as-built RC square column and a reinforced concrete bridge bent retrofitted using buckling restrained braces (BRBs) was
experimentally evaluated using quasi-static cyclic loading protocols aiming to reflect subduction zone earthquake
demands up to displacement ductility. The buckling restrained braces were designed as replaceable elements in order to
take the earthquake-induced energy and dissipate it through nonlinear hysteretic behavior. Two BRB designs were
considered in the study in an effort to assess the influence of BRB stiffness on the overall structural performance. The
results of these large-scale experiments successfully demonstrated the effectiveness of utilizing buckling restrained braces
for achieving high displacement ductility of the retrofitted structure, while also controlling the damage of the existing
vulnerable reinforced concrete bent up to the design performance levels. The potential of improving the overall seismic
behavior and the design performance levels with BRBs offers structural design professionals a viable method for
performance driven retrofit of reinforced concrete bents.
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