ABSTRACT
A lot of assumptions,simplifications and approximations are made in the deterministic design of structures in the process of substituting a real physical system, whose behaviour is inherently random, with a mathematical model. Resort is therefore often made to the application of safety factors and allowable limits which in reality represent factors of ignorance of actual operating conditions and true performance capabilities of a structure. Recognising that safety involves a consideration of random variables, it is obvious that the approach to the analysis of structural safety is through the use of probabilistic methods. The deterministic and probabilistic methods of analyses are both employed to check the performance of the roof truss of a multi-purpose indoor sports hall in Bauchi which failed during construction. In the deterministic analysis, real physical systems are substituted with deterministic equations which do not contain terms corresponding to random forces. The probabilistic method takes into account the variabilities in material properties and random nature of loading. The results show that although the design of the truss satisfies the determinsitic requirements, the probabilistic check invalidates the adequacy of the design. The actual axial stress on the most loaded truss member is 119.85N/mm2 while the permissible stress is 123N/mm2. The probability of failure is 0.456 corresponding to a safety index of 0.110. This level is grossly inadequate on the basis of the level stipuated for this class of structure. It is therefore concluded that the collapse of the roof could have been initiated by the failure of the most loaded member.