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Inner lever arm in EN 1992-1-1, clause 6.2.3 (3) is defined as a distance of forces in tensile and compression chord, it follows that is it the distance of position resultant of tensile force (tensile reinforcement) and position of resultant of compressive force (compressive reinforcement and compressive concrete). For better overview, there is calculated the perpendicular projection inner lever arm to straight line perpendicular to neutral axis (slope line plane of equilibrium), called zrec.
Except of value inner lever arm, there is calculated part of inner lever arm only:
There are some exceptional cases, when inner lever arm is not calculated from plane of equilibrium:
In this cases, the inner lever arm and parts of inner lever arm is calculated according to formula
z = zrec = Coeffz ∙ d
z+ = zrec+ = z- = zrec- = 0.5 ∙ z
where
