Seismic Design of Tunnels - Parsons Brinckerhoff

Port and Harbor Facilities
Neither standard seismic codes nor universally accepted seismic design criteria exist
for waterfront facilities such as berthing (wharf) structures, retaining structures, and dikes.
Recent advances in seismic design practice for other facilities, however, have prompted
the development of several project specific seismic design criteria for waterfront facilities
in high seismic areas (POLA, 1991; Wittkop, 1991; Torseth, 1984).
The philosophy employed in the design, again, is based on two-level criteria:
• Under an Operating Level Earthquake (OLE), a smaller earthquake, the structures
should experience little to no damage and the deformations of wharf structures should
remain within the elastic range. Generally, the OLE is defined to have a probability of
exceedance of 50 percent in 50 years.
• Under a Contingency Level Earthquake (CLE), a larger earthquake, the structures
should respond in a manner that prevents collapse and major structural damage,
albeit allowing some structural and nonstructural damage. Damage that does occur
should be readily detectable and accessible for inspection and repair. Damage to
foundation elements below ground level should be prevented (POLA, 1991).
Generally, the CLE is to have a probability of exceedance of 10 percent in 50 years.
The risk level defined for the CLE is similar to that of the design earthquake adopted in
bridge and building design practice.
Oil and Gas Pipeline Systems
The seismic design guidelines recommended by ASCE (Nyman, et al, 1984) for oil
and gas pipeline systems are in many ways similar to the principles used in the design for
other important facilities. For important pipeline systems, the design should be based on
two-level earthquake hazard:
• The Probable Design Earthquake (PDE), the lower level, is generally associated with a
return period of 50 to 100 years.
• The Contingency Design Earthquake (CDE), the higher level, is represented by an
event with a return period of about 200 to 500 years. The general performance
requirements of the pipeline facilities under the two design events are also similar to
those for other facilities.
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