DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

Chapter 4 Design Earthquake Ground Motions
4.1 General
Level 1 and Level 2 Earthquake Ground Motions shall be determined in accordance
with the provisions in Section 4.2 and 4.3, respectively. However, design earthquake
ground motions at a bridge site can be determined in consideration of the information
on earthquake histories around the bridge site, active faults, earthquakes occurring in
the plate-boundaries near the site, geological structures, geotechnical conditions, and
existing strong motion records, if this procedure is more appropriate.
4.2 Level 1 Earthquake Ground Motion
(1) Level 1 Earthquake Ground Motion shall be determined in accordance with the
acceleration response spectrum specified in (2).
(2) The acceleration response spectrum shall be provided, in principle, at the ground
surface to be considered in seismic design prescribed in Section 4.6, and shall be
calculated by Equation (4.2.1).
S c cDS
0
Z ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (4.2.1)
where
S : Acceleration response spectra for Level 1 Earthquake Ground Motion
(rounded to an integral by neglecting decimals)
c Z
: Modification factor for zones specified in Section 4.4
c D
: Modification factor for damping ratio. It shall be calculated by Equation
(4.2.2) in accordance with the damping ratio h.
1.5
c D 0.5 ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (4.2.2)
40h
1
S0 : Standard acceleration response spectra (gal) for Level 1 Earthquake
Ground Motion. It shall be a value in Table 4.2.1 in accordance with the
ground type specified in Section 4.5 and the fundamental period T.
7