DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

(6) When an isolation bearing is used as a horizontal force distributing structure
during an earthquake, rather than a seismic force reduction structure through
energy absorption, design structural response based on the damping ratio of the
bridge shall not be reduced.
9.2 Verification of Seismic Performance of Seismically-Isolated Bridges
(1) Verification of seismic performance of a seismically-isolated bridge shall be based on
the provisions specified in Section 5.5, together with proper consideration of the
bridge properties. In calculating seismic response of the isolation bridge, the
isolation bearing can be modeled in accordance with the provisions provided in
Section 9.3.
(2) Allowable ductility ratio of Reinforced Concrete Columns in a seismically-isolated
bridge shall be obtained by Equation (9.2.1)
u y
μ m
=1
・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (9.2.1)
m
y
where
μ m : Allowable ductility ratio of an Reinforced Concrete Columns in
seismically-isolated bridge
α m : Safety factor used for the calculation of the Reinforced Concrete Columns. αm
shall be calculated by Equation (9.2.2)
α m = 2α ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (9.2.2)
α : Safety factor used for calculation of the allowable ductility ratio of the
Reinforced Concrete Columns, and is specified in Table 10.2.1
δy,δu : Yield displacement and ultimate displacement of the Reinforced Concrete
Columns, respectively, and shall be calculated by referring to Section 10.3
(3) Isolation bearings shall be verified in accordance with the provisions in Chapter 15.
In addition, only isolation bearings having the fundamental functions specified in
Section 9.4 shall be basically selected.
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