Ohb

>1500

vs is the average shear wave velocity for top 30 m of a site. N is the average standard penetration test blow count for top 30 m of a site.

Nch is the average standard penetration test blow count for cohesionless layers of top 30 m of a site. su is the average undrained shear strength of cohesive layers for top 30 m of a site.

Seismic force effects from different vibration modes shall be combined. For modal response closely spaced in frequency and ground motion in one direction, the complete quadratic combination (CQC) method shall be used. For combining the contribution of orthogonal and uncorrelated ground motion components to a single seismic load case, the square root sum of the squares (SSRC) method or 100 to 40% rule shall be used.

For a bending moment, the combination rules are as follows:

SSRC combination:

100 to 40% combination:

For circular columns, the vector moments and axial forces shall be obtained for biaxial design: SSRC combination:

• For bridges with skew angle less than 10°, the maximum of sjM2 + (0.4My)2 and t/M2 + (0.4Mx)2 with the maximum axial load ±P

• For bridges with skew angle greater than 10°, ^JM^ + M2 with the maximum axial load ± P

100 to 40% combination:

• The maximum of p(MxLC1)2 + (MyLC1 )2 and p(MxLC2)2 + (MyLC2)2 and p(MxLC3)2 + (MyLC3)2 with the maximum axial load ± P

where subscripts x and y represent two horizontal axes, x-x and y-y, respectively; superscripts L, T, and V indicate the longitudinal, transverse, and vertical directions, respectively; and superscripts LC1, LC2, and LC3 are load cases 1, 2, and 3, respectively.

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