Torsional longitudinal reinforcement
Additional tensile forces caused by torsion are calculated from the equation 6.28 in EN 1992-1-1
Fsdt = |TEd| / (2 ∙ Ak) ∙ uk ∙ cot θ
where
| TEd |
torsional moment |
| Ak |
the area enclosed by the centre-lines of the thin-walled closed cross-section, including inner hollow areas, see "Calculation of basic characteristics" |
| uk |
circumference of the area enclosed by the centre-lines of the thin-walled closed cross-section, see "Calculation basic characteristics for shear" |
| θ | Angle between concrete compression strut and beam axis perpendicular to the shear force, see "Angle between concrete compression strut and beam axis" |
The required cross-sectional area of the longitudinal reinforcement for torsion is calculated in case, that sum of design axial forces (NEd) and Additional tensile forces caused by torsion (Fsdt) is tensile (bigger than 0). This area is calculated with following preconditions:
- reinforcement is designed only for pure tension
- longitudinal reinforcement is equally distributed on each edge of cross-section
In a simplified way said, the longitudinal reinforcement for torsion is designed according to formula below,
ΔAs = Ftsd / σsd
where
| Fsdt | additional tensile force caused by torsion |
| σsd |
design value of stress in longitudinal reinforcement - fyd |
Additional tensile forces caused by shear forces is taken into account in design of statically required reinforcement by shifting of bending moments, see "Additional tensile forces caused by shear and torsion (shifting of bending moments)"