2.5.8 Minimum Longitudinal Reinforcement

Minimum Longitudinal Reinforcement

The statically required longitudinal reinforcement is now compared to the minimum reinforcement. Unfortunately, none of the standards available in RF-CONCRETE Surfaces provides any regulations on the minimum reinforcement for shells. As a criterium, it is therefore analyzed for which constellation of the moment and axial force the element is more likely to be a wall (mainly subjected to compression) or a plate (mainly subjected to bending). The distinguishing criterion is the related load eccentricity e_d/h in the ultimate limit state (ULS):

$\frac{e_{d}}{h} = \frac{m / n}{h}$

where

Table 2.2
m	moment of linear plate analysis (ULS)
n	axial force of linear plate analysis (ULS)
h	plate thickness

Since there are moments and axial forces both in x- and y-direction in a design point, the related load eccentricity per design point is the largest quotient from moment over axial force of both directions.

In RF-CONCRETE Surfaces, the following is uniformly specified for all standards:

Table 2.2
$\frac{e_{d}}{h} > 3.5$	mainly subjected to bending → reinforcement rules for plates
$\frac{e_{d}}{h} \leq 3.5$	mainly subjected to compression → reinforcement rules for walls

This regulation can be found in EN 1992-1-1, clause 9.3: Solid slabs and clause 9.6: Walls.

The minimum reinforcements are described in chapter 2.3.7 and chapter 2.4.5 in the reinforcement rules for walls and plates.

In our example, where the system is mainly subjected to bending, the following minimum reinforcement is shown in the design details.

Image 2.77 Minimum longitudinal reinforcement

Parent section

2.5 Shells