In BS EN 1992-1-1:2004, the method of designing for vertical shear is based on a truss analogy with a diagonal strut acting at an angle θ. This strut action means that there must be a tension force developed in the longitudinal reinforcement which is additional to that arising from bending action.

To resist this tension force, an area of reinforcement additional to that required to resist bending is required.

The total area of longitudinal tension reinforcement in each of the regions then becomes;

A_stt,reqd,i = A_st,reqd,i + A_swa,reqd,i

where

A_st,reqd,i = the area of longitudinal reinforcement required to resist bending as appropriate in region " i"

A_swa,reqd,i = the area of longitudinal reinforcement required to resist the additional tension force from vertical shear in region " i"