Safety factor of structure is defined in terms of frequency distribution of quotient of resistance and load, and its relation with probability of structural failure is developed; concepts of structural reliability and of risk of failure are introduced and examined as basis of safety analysis for finite operational life of non-redundant and of redundant structures; safety analysis based on logarithmic-normal and extremal distributions of resistance and of load.

General solution is given in matrix form for analysis of member curved or segmental in space and continuous between 2 supports; solution also yields general slope deflection equation which involves stiffness matrix; stiffness matrix contains all stiffness and carryover factors for ends of member.