The reliability of steel trusses is calculated in the paper.The influence of truss topology on reliability is analysed.Five cases of truss are discussed.The reliability analysis concerns the formulation of the limit state,calculation of the failure probability and determination of the reliability index.There are four groups methods commonly used for the structural reliability assessment but only one of them,used in the paper,is definitely most complete.It is the system approach.This method contains both determining reliability models and reliability analysis.To determine reliability model,the spectral analysis of the linear stiffness matrix is used.To identify all possible non-repeatable combinations of removed rods transforming truss to a mechanism the program based on the application of the finite element method was created.For each truss the reliability index is estimated by evaluating its lower and upper bounds.The lower bound is evaluated by assuming that the truss behaves itself like a statically determinate truss,i.e.,a failure of one element is equivalent to the failure of the whole structure(serial system).The upper bound is evaluated by assuming actual connections and interactions between the rods by using generated reliability model(mixed system).In this case the reliability index is computed using the program developed by the authors.Additionally,the approximation method is proposed as verification.
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