Themainsteps in a structural reliabilityanalysisare:a)Establish a targetreliability, or a decision model.b) ldentify all significant modes of failure of the structure oroperation underconsideration.c) Formulate a failure criterion in terms of a limit-state function foreachmodeoffailure.d) ldentify stochastic variables and parameters in the limit-statefunctionsandspecifytheirprobabilitydistributions.e)Calculate the reliabilityagainstfailurefor eachmode offailure ofthestructureoroperationunderconsideration.t) Assess whether the estimated reliability is sufficient and modifytheconceptifnecessaryg) Evaluate the results of the reliability analysis with respect toparametricsensitivityconsiderations.1
The main steps in a structural reliability analysis are: a) Establish a target reliability, or a decision model. b) Identify all significant modes of failure of the structure or operation under consideration. c) Formulate a failure criterion in terms of a limit-state function for each mode of failure. d) Identify stochastic variables and parameters in the limit-state functions and specify their probability distributions. e) Calculate the reliability against failure for each mode of failure of the structure or operation under consideration. t) Assess whether the estimated reliability is sufficient and modify the concept if necessary. g) Evaluate the results of the reliability analysis with respect to parametric sensitivity considerations. 11
Target ReliabilityTarget Reliabilities have to be met in design in order toensure that certain safety levels are achieved. A reliabilityanalysis can be used to verify that such a target reliabilityis achieved for a structure or structural element. Adifficulty in this context is that the uncertainties includedun a structural reliability analysis will deviate from thoseencounteredinreallife12
Target Reliabilities have to be met in design in order to ensure that certain safety levels are achieved. A reliability analysis can be used to verify that such a target reliability is achieved for a structure or structural element. A difficulty in this context is that the uncertainties included un a structural reliability analysis will deviate from those encountered in real life. Target Reliability 12
Limit States?Ultimate limit state?Fatigue limit state·Serviceability limit state·Accidental limit state13
Limit States •Ultimate limit state • Fatigue limit state • Serviceability limit state •Accidental limit state 13
Methods for reliability analysis: Structural reliability methods are traditionally classifiedaccording to Level, Moment and Order.Level refers to the extent of information about thestructural reliability problemthat is provided and used..Moment refers to the order of statistical momentsapplied to represent an uncertain variable and itsprobability distribution..Order refers to the order of the polynomial applied forlocalapproximationofthelimit-statesurface.14
• Structural reliability methods are traditionally classified according to Level, Moment and Order. • Level refers to the extent of information about the structural reliability problem that is provided and used. • Moment refers to the order of statistical moments applied to represent an uncertain variable and its probability distribution. • Order refers to the order of the polynomial applied for local approximation of the limit-state surface. Methods for reliability analysis 14
.Level I methods are deterministic reliability methodsthat use only one 《characteristic》 value to describeeach uncertain variable. Load and resistance factorformats,andallowablestressformats,areexamples ofLevelImethods?Level I methods correspond to standard deterministicdesign methods. The partial coefficients usuallyapplied in such methods may be calibrated to aspecified reliability level by a higher level reliabilitymethod.15
• Level I methods are deterministic reliability methods that use only one «characteristic» value to describe each uncertain variable. Load and resistance factor formats, and allowable stress formats, are examples of Level I methods. • Level I methods correspond to standard deterministic design methods. The partial coefficients usually applied in such methods may be calibrated to a specified reliability level by a higher level reliability method. 15