Reliability assessment of redundant safety systems with degradation

Reliability of transport equipment plays a crucial role in providing safety for passengers. Safety systems of transport equipment perform safety functions with assigned safety integrity levels (SIL). If the reliability of a safety system is not sufficient, it has to be improved till the required level. This can be done by improving maintenance, enhancement of diagnostics or by applying redundancy.<br/>To conclude that reliability value is sufficient (or not), it is necessary to calculate its value before and after reliability improvement. Such calculations can be done analytically or by a simulation approach. Usually simulation approach is time consuming for a large number of simulations. Small number of simulations leads to an error in the results. Therefore analytical methods are often welcomed by both – scientists and practitioners.<br/>This thesis investigates analytical methods of reliability calculation focusing on systems with degradation. Analytical formulas of reliability calculation have limitations for systems with degradation due to non-constant failure rates (in this thesis they are modelled by Weibull distribution). These limitations have been shown in the example of a braking system of moving walks in Chapter 3: analytical methods are mainly applicable only to systems with constant failure rates especially in the case of redundant systems