Stress fields model

If we represent the inclined struts in the form of stress fields, we obtain two fans with stresses that vary hyperbolically in the radial direction. The resultant of the stress field has the same direction and intensity as the corresponding compressed strut in the truss model.

Stress fields model

We can note a region ABC in the stress field above where the two fans overlap, which constitutes a slight violation of the failure criterion. This overlap is due to the fact that the transverse reinforcements are arranged up to the support, meaning that the first fan, which transmits the load to the stirrups, overlaps with the lower bar and the second fan, which carries the load from the top of the stirrups to the support. If we place the stirrups only up to point B, the intermediate zone disappears, as shown in the figure below.

Stress fields model without the indermediary zone ABC