Abstract: Structural mechanics is directly used for engineering structural design,in which exists a vast amount of uncertain (including random, fuzzy and unascertained) information. With the treatment of random information in engineering design, theory of structural reliability and theory of random vibration were developed. Similarly, along with the treatment of fuzzy and unascertain information, some new branches of structural mechanics are developed. They are uncertain optimum design of structures, generalized (fuzzy-random) theory of reliability, theory of fuzzy random vibration and fuzzy earthquakeengineering. The fundamental ideas of those fields are briefly introduced in this paper.