D1.F.4.2 Minimum Flexural Reinforcement

The code specifies to dispose a minimum area of flexural reinforcement where tension reinforcement is required.

As a minimum bound, the condition that is given in 9.6.2.1is used. Although it is intended only for prestressed beams, it may be used also in reinforced concrete beams and control in odd circumstances such as where the specified cover is extremely large. The bending strength of the section is designed to be at least 1.2 Mcr, where the cracking moment is assumed to be applied to each axis separately as uniaxial bending. No simultaneous biaxial moments are considered. The cracking moments about each axis are calculated to cause the stress in the extreme tension fiber to reach fr. In order to account for a possible varying of elastic modulus (Ec) values, the following formula is used ignoring the effect of the inertia product (Ixy):

M_{c r (r e g i o n)} = \frac{σ_{c r (r e g i o n)} E_{c} I_{c}}{E_{c (r e g i o n)} c_{(r e g i o n)}}

where

σ_cr(region)	=	the flexural tension strength for a region
E_c(region)	=	the modulus of elasticity for a specific region
c_(region)	=	the distance from the neutral axis to the extreme fiber of a region
E_cI_c	=	the integrated product of the inertia and elastic modulus for the entire section
fr	=	the modulus of rupture calculated in accordance with Clause 19.2.3.1
λ	=	calculated according to Clause 19.2.4.2

The cracking moment is individually calculated for each axis and only considers a particular axis if there is a considerable bending moment about that axis. The sign of the acting moment is also considered.

This minimum bound is considered only when the 9.6.1.2 or 9.6.1.3 is also applied