Earthquake Design Criteria for Subways

Earthquake effects on underground structures comprise faulting and shaking. The design criterion for underground structures is ductility to absorb imposed distortions without losing capacity to carry static loads, rather than resistance to inertial forces. Curvature distortion may be calculated from a design earthquake spectrum giving amplitudes and wave lengths. Shearing distortion, resulting from lag of soil behind bedrock displacement, may be calculated from seismic velocity of ground and depth of overburden. Usually reinforced concrete structures have sufficient ductility to absorb seismic deformations elastically, so no special design is required for earthquake resistance. Detailed earthquake design criteria for San Francisco BART subways are included. These contain provisions to be made when plastic distortions are imposed on the structure.