Principle of the Strut-and-Tie Model

This chapter traces the method of the strut-and-tie model (STM) back to its roots, the limit analysis. Then the method as a lower-bound solution is introduced by first explaining why the method is a necessity in those regions where the bending theory cannot be applied. The method has come as an appropriate approach to treat all structural concrete elements and components consistently and in a unified manner. The chapter covers the limit theorems with both the upper- and lower-bound solutions, the principle of the method of STM, the approaches to develop an STM, and the constituent elements of the model: struts, ties, and nodes. The regions where the bending theory is applicable, B-regions, are distinguished from those disturbed regions, D-regions, where this theory cannot be applied. The chapter also gives a historical sketch on (1) the development of the truss model which is the basis for the design of B-regions; (2) the start of the STM from the limit analysis; and (3) the major development of the STM method with connection to the truss model for unified and consistent design of structural concrete.