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LRFD by separate load factors (γ) for dead load, live load, wind-wave-current
load, earthquake load and wave dynamic load. Resistance factors (ϕ) vary for
pile capacity, beam bending, axial compression, hydrostatic pressure, etc.
Together, these load and resistance factors provide a level of safety close to
present practice, yet provide more uniform safety and economy.
Calibrated β-values ranged from 2.0 to 2.8 for a 20-year service life
with a 100-year loading event used as the reference load level. Similar val-
ues for the North Sea were developed by Turner et al. (1992). Recently,
International Organization for Standardization (ISO) 19902:2007, Fixed
Offshore Steel Structures, which was based on API RP 2A-LRFD and
expanded to include loading specifics for international locations, became
available and is referenced in the International Electrotechnical Commis-
sion (IEC) offshore wind turbine design standard (i.e., IEC 61400-3) as the
offshore structural guidance document.
Other Civil Infrastructure Applications
As noted above, probability-based design of buildings and bridges has
focused on member or component limit states and has measured relia-
bility by making use of the reliability index β. More recent applications
of risk-informed decision making to civil infrastructure, brought about
in part by the move toward performance-based engineering, have con-
sidered system behavior and expressed performance through limit state
probabilities rather than through use of the reliability index. These devel-
opments have been made possible through advances in structural com-
putation, which now make nonlinear dynamic analysis of complex
building and bridge structures feasible in design. Several standards and
guidelines have begun to adopt such concepts.
ASCE 7-10 Commentary 1.3.1.3 ASCE Standard 7-10 has implemented
a new general design requirement for performance-based procedures. The
commentary to these procedures contains two tables with acceptable reli-
ability levels: the first stipulates annual limit state probabilities and relia-
bility indices for nonseismic events, and the second provides anticipated
probabilities of structural failure for earthquakes. These acceptable relia-
bility levels are dependent on the risk category of the structural facility and
the nature of the structural failure involved. In nonseismic design situa-
tions, the acceptable annual probability of failure ranges from 3 × 10 −5 /year
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