DESIGN SPECIFICATIONS FOR HIGHWAY BRIDGES - IISEE

elative displacement obtained from the dynamic analysis shall be taken as uR in
Equation (16.2.1).
(2) For a skew bridge with superstructural shape meeting Equation (16.5.1), the
seating length shall satisfy the provisions in (1) and be calculated by Equation
(16.2.4). For an asymmetric skew bridge in which the two front lines of the bearing
supports at both ends of the superstructure are oblique, SE θ shall be calculated
with use of a smaller skew angle.
S Eθ ≧ (L θ / 2) (sin θ – sin (θ – α E )) ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.4)
where
SE θ : Seating length for the skew bridge (m)
L θ : Length of a continuous superstructure (m)
θ : Skew angle (degree)
α E : Limit of unseating rotation angle (degree), α E
can generally be taken as 5
degrees.
(4) For a curved bridge with superstructural shape meeting Equation (16.5.2), the
seating length shall satisfy the provisions in (1) and be calculated by Equation
(16.2.5).
sin
S Eφ ≧ δ E + 0.3 ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.5)
cos( / 2)
δ E = 0.005φ+ 0.7 ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ (16.2.6)
where
SE φ : Seating length for the curved bridge (m)
δ E : Displacement of the superstructure toward the outside direction of the curve
(m)
φ: Fan-shaped angle by the two ends of a continuous girder of a curved bridge
(degrees)
16.3 Unseating Prevention Structure
(1) Ultimate strength of an unseating prevention structure shall not be less than the
design seismic force determined by Equation (16.3.1). Here, the ultimate strength
may be taken as 1.5 times the allowable stress. In addition, the design allowance
85