Parallel Systems of Series Subsystems

Throughout this paper we consider the structure at a fixed point in time and the structure is assumed to depend only on the state of its components. Moreover, only two states are considered: functioning and nonfunctioning of the components and the system. Any system can be represented as a Series System of Parallel Subsystems (SSPS) or as Parallel System of Series System (PSSS). High reliability SSPS are handled by PROBAN, a program developed at Det Norske Veritas and The Technical University of Munich. A SSPS may be reformulated as PSSS, this may however be very large. The scope of this paper is therefore to develop methods for computing or bounding the reliability of parallel systems of series subsystems. In a number of applications it is desired to deal with such systems. One example is the computation of the reliability of the tether system of a Tension Leg Platform. Other examples of PSSS in Structural System Reliability are provided in Madsen and Skjong (1984) and Madsen et al (1986). Barlow and Proschan (1975) provides examples from other fields.