EP 1130-2-500
27 Dec 96
(1) For steel design, major structural components are designed to a constant value of the
reliability index, typically about 3.0; however, connections are designed to higher reliability index
values, perhaps 5.0, as engineers have always desired to avoid problems at connections. A
complex steel frame is designed such that each component meets a target reliability index value,
which may vary, but a "system reliability" calculation is not routinely done in building design.
However, target reliability indices may be established for critical lock and dam or hydropower
components and performance modes, and O&M priorities will be directed at ensuring that these
targets are met or exceeded.
(2) For initial use in reliability assessment, the target reliability values presented in Table
D-1 should be used. A hazard function plot of reliability vs time for major performance modes
should be developed. The objective of the Operation and Maintenance program would be to keep
the reliability for each significant mode above its target value for the foreseeable future.
D-6. Target Reliability Values. Reliability indices are a relative measure of the current condition
and provide a qualitative estimate of the structural performance. Structures with relatively high
reliability indices will be expected to perform their function well. Structures with low reliability
indices will be expected to perform poorly and present major maintenance problems. If the
reliability indices are very low, the structure may be classified as a hazard. Working from a
sufficiently large experience base, it should be practical to make some estimates of expected
structural performance with some engineering judgement. A large experience base exists within
USACE and studies are planned to collect, organize and analyze these operation and maintenance
records. The target reliability values shown in Table 1 should be used in general. Case-by-Case
refinements should be conducted in consultation with and approved by CECW-ED.
References.
D-7.
a. AISC, Load & Resistance Factor Design, Manual of Steel Construction, 1st Edition
1986, AISC.
b. Beim, G.K. and Hobbs, B.F., June, 1995, Development and Use of Subjective
Probabilities and Event Trees for Water Resources Investments, Draft report to CEIWR, Ft.
Belvoir, VA.
c. Benjamin, J. and C.A. Cornell, (1970) Probability and Statistics, and Decision for Civil
Engineers, McGraw-Hill, New York.
d. Ellingwood, Bruce R., Engineering Reliability and Risk Analysis for Water Resources
Investments: Role of Structural Degradation in Time-Dependent Reliability Analysis, Contract
Report ITL-95-3, July 1995, Waterways Experiment Station, Vicksburg, MS.
e. Wolff, Thomas F. and Weijun Wang, Jan. 1992, Engineering Reliability of Navigation
Structures, Report prepared under DACW 39-91-C-0041.
Table D-1
TARGET RELIABILITY INDICES
EXPECTED
POTENTIAL
PERFORMANCE
BETA
OF UNSATISFACTORY
PHYSICAL
D-5
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