To overcome the deficiency that the safety membership function of a structure or a system in safety engineering sometimes involves subjectivity in the application of profust reliability theory,a preliminary study was made for finding out the rootstock of the performance fuzziness of a random system.

In this paper,the writers calculated the credibility rate of combination-logic circuit with redundant item,and they also pointed out shield the out-error which input cause,the combination-logic circuit must be inter-digital conjunction.

Traditional probabilistic reliability method has been widely accepted and used to dealing with uncertainties in engineering.

Mathematical model of topology optimization design of random structure was established,in which the mean of structural weight was taken as minimization objective function,the structural shape topology information was taken as design variables,and the probabilistic reliability index of structural foundamental frequency was taken as constraint conditon.

A mathematical model for topology optimization design with a random structure is established,in which the minimum mean of structural weight is taken as the objective function,the structural shape topology information is taken as design variables,and the probabilistic reliability index of structural total strain energy is taken as the constraint condition.