20613 Response Modification Factor R

It is generally recognized that it is uneconomical, sometimes impractical, and impossible to design a bridge to resist large earthquake elastically. Columns are assumed to deform inelastically where seismic forces exceed their design levels, which is established by dividing the elastically computed force effects by the response modification factor R. The R-factors specified in the following were based on an evaluation of existing test data, engineering judgement, and the equal displacement principle as shown in Figure 20.14. It is used in principle for the conventional ductile design. For substructures

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FIGURE 20.14 Basis for conventional ductile design [37].

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FIGURE 20.14 Basis for conventional ductile design [37].

TABLE 20.8 Recommended LRFD Guidelines — Base Response Modification Factor for Substructures, Rb (ATC/MCEER Joint Venture, 2001)

Performance objective Life safety Operational

Substructure element

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