The strut-and-tie method (STM) was introduced in 1994 in the AASHTO load and resistance factor design specifications. Within the strut-and-tie design approach, an internal truss, consisting of concrete struts and steel ties, carries the loadings through the D-region to its supports or boundaries. To create this truss, reinforcing or prestressing steel is selected to serve as the ties, whereas dimensions for struts and joints (nodal zones) are chosen so that they have sufficient strength. The STM design process typically requires selecting an appropriate internal truss, adjusting and refining the truss, and conducting multiple truss analyses, for different load combinations. Completing this design process by hand can be time consuming. The computer-aided strut-and-tie (CAST) design tool is being developed to overcome this challenge. CAST provides a single graphical interface that enables the designer to sketch and analyze the idealized truss, to select member dimensions and tie reinforcement, to readily adjust all design variables, and to create a printout of the final design.
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