Concrete structural elements-members can be divided into two general regions: flexural regions (Bernoulli or B-regions) and regions near discontinuities (Disturbed or D-regions). A Strut and Tie model should be developed to model the flow of forces through the D-region. In general, any part of a member outside of a B-region belongs to a D-region, while B-regions are more easily checked with conventional methods described by national codes.


Pic.1. Samples of D-regions


A Strut and tie Model usually is a simple schematization, where stress lines or cracks are strut and/or tie segments in tension or compression:


Pic. 2. The schematization of Struts and Ties

More than one way of schematization is possible.

Distribution of stresses in the conceptual Strut and Tie model:

Strut Compression element Concrete
Tie or stirrup Tension element Reinforcement
Node Nodal connection Concrete