SHEAR DESIGN INTEGRATED in THE DESIGN CONCEPT of STRUT-and-TIE MODELS for STRUCTURAL CONCRETE
More than 100 years ago the truss model was proposed as a model for the shear design of structural concrete members, but since then the shear capacity has puzzled researchers and designers until now. In the last two decades many efforts were made to re-introduce models for designing structural concrete in terms of strut-and-tie models. These activities were enhanced by damages and failures of structures, and therefore, a brief review is given on the design concepts in present codes. As an alternative to present code concepts, a modern design concept is presented based on strutand-tie models. This concept addresses discontinuity regions (D-regions) with the same emphasis as B-regions with the design for shear and flexure. Some examples are presented for the interaction of B- and D-regions The present state of relevant codes on the methods for the shear design is outlined. A modern design method is presented for members with stirrups which is based on the classical addition of a concrete and a steel term. In contrast to the theory of plasticity and many present codes, the strut angle is made dependent on the magnitude of the shear force. The shear transfer of members without shear reinforcement is treated also based on a truss model. Briefly a theory is presented for the calculation of the shear capacity, which clearly explains the size effect and the role of the reinforcement ratio. An example is given for the necessity to introduce modeling with concrete tension fields in the design concept of strut-and-tie models.