EP 1130-2-500
27 Dec 96
results of the analysis for each alternative. The following represent some potential alternative
plans that should be evaluated and compared.
- Advance maintenance strategy. Advance maintenance consists of expenditures in
excess of routine O&M that reduces the likelihood of some emergency repairs and temporary
service losses, or the rate of service degradation. Under this scenario, one must evaluate the
effect that probabilities and consequences of the strategy have on expected service disruptions
and reliability.
- Scheduled repair strategy. Assess the components of the feature in terms of the service
disruption probabilities and consequences to the reliability of the structure. Based on this
assessment, stockpile replacement parts and make other preparations on this assessment to
reduce the time of expected project service disruption.
- Scheduled rehabilitation strategy. The scheduled rehabilitation strategy requires that
the "optimum" rehabilitation timing be identified based on service disruption rates, service
degradation and their economic cost.
- Immediate rehabilitation strategy.
(4) Summary Statistics. Provide a table to illustrate the cost, benefits, net benefits and
benefit to cost ratios of the base condition and each alternative considered.
f. Engineering Considerations.
(1) Reliability Analysis
(a) General. Present a summary of the reliability analysis for the base condition and each
alternative. The reliability of the various alternatives must be investigated in order to evaluate
the relative merit of each alternative with respect to the base condition. In addition, if the base
condition assumes that emergency repairs will be made to unreliable components or features, a
post emergency repair reliability analysis must be made of the component or feature. Enclosure
2 provides an introduction to the principles and procedures to follow in conducting a reliability
analysis, and the reporting requirements. Additional considerations are provided below.
(b) Probability of Unsatisfactory Performance. The reliability of a component or
structure shall be stated in terms of the probability y of unsatisfactory performance of the feature.
Unsatisfactory performance of a component maybe indicated at various levels of performance,
depending upon the consequences of that performance level, from minor deflections to complete
collapse of a structure. Probabilities of unsatisfactory performance should be calculated for a
range of performance levels, however, failure scenarios which indicate threats to public safety
should not be assigned probabilities using the procedures outlined herein. While these situations
may be identified using reliability analysis techniques, they should be considered to be
emergency situations and remediated outside to the major rehabilitation program. Probabilities
of unsatisfactory performance must be calculated using the analytical procedures outlined in
Appendix D, using one of four methods;(1) Reliability Indices; (2) Hazard Functions; (3)
Historical Frequency of Occurrence Analyses and (4) Expert Elicitation. Expert Elicitation
should only be used to establish subjective probabilities of unsatisfactory performance for
preliminary screening purposes to determine the components or features which need further
study, or when there is insufficient data to develop the probabilities from historical frequencies
B-6
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