2

where BL is the response reduction factor for long period structures as specified in Table 20.7, BS is the response reduction factor for short period structures as specified in Table 20.7, g is the acceleration due to gravity (9.8 m/s2), and A is the lateral displacement of the pier; taken as 1.3 times the yield displacement of the pier when the long period equation governs.

The lesser of Equations 20.8 and 20.9 shall be used to assess Cs for two-level earthquakes. The required lateral strength of the bridge is Vn = CsW where W is the weight of the bridge responding

TABLE 20.7 Recommended LRFD Guidelines — Capacity Spectrum Response Reduction Factors for Bridge with Ductile Piers [37]

Earthquake

Performance level

Bs

Bl

50% PE in 75-year

Life safety

0 0

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