Determination of strut-and-tie models using evolutionary structural optimization

This paper introduces a method to determine strut-and-tie models in reinforced concrete (RC) structures using evolutionary structural optimization (ESO). Even though strut-and-tie models are broadly adapted in the design of reinforced concrete members subjected to shear and torsion, conventional methods can hardly offer useful models of RC members subjected to complex loadings and geometry conditions. In this paper, the basic idea of the ESO method is used to determine more rational strut-and-tie models. Since an optimum topology of structures, finally obtained by the ESO method, usually represents a truss-like structure, the ESO method using truss elements can effectively be used in finding the best strut-and-tie models in RC structures. To prevent the structural instability that may occur during the evolutionary optimization process, a brick element composed of six truss elements is designed as a basic element unit. Systematic removal of each brick element that has the least virtual strain energy follows, and the optimal load transfer mechanism of an RC structure, which is equivalent to the optimal topology of the strut-and-tie model, is finally characterized on the basis of an optimization criterion of minimizing the total elastic strain energy of the structure. Several RC structures are used as examples to demonstrate the capability of the proposed method in finding the best strut-and-tie model of each RC structure and to verify its efficiency in application to real design problems.