In accordance with Eurocode 2 and its French Annex, the section of the longitudinal reinforcements must be such that :
is the minimum cross-section required in order to control cracking.
corresponds to the non-fragility condition :
In the particular case of piles, the NF P94-262 standard (table Q.3.4.2.2) recommends a longitudinal reinforcement according to the cross section of the pile ():
If the cross-sectional area is ², then
If the section ² is A_c\leq1.0m²A_{s,min}\geq0.0025m²$
If the cross-sectional area ², then
Maximum section
The section of longitudinal reinforcement must not exceed, outside overlapping areas, the maximum value allowed by Eurocode 2 is:
Anchoring length
The ultimate adhesion stress between the steel bar and the concrete
Compressive strength of concrete (MPa) (its value depends on the situation)
Adhesion conditions are considered good = 1.0 // poor= 0.7
Parameter that depends on the diameter of the bar
If
If ( in mm)
Reference anchor length: this is the length required to anchor a bar where a force is developed, with a limit adhesion stress assumed to be constant.
where is the stress in the bar, computed at the section from which the anchor is measured:
where is considered for Fundamental ULS.
Anchor length
Coefficient
Description
Influence factor, depends on the shape of the bars (straight anchorage)
Influence factor, depends on the coating (straight anchorage) with where is the coating of the longitudinal bar and is the distance between the longitudinal bars
Influence factor, depends on confinement by the transversal reinforcements not welded to longitudinal reinforcements
Influence factor, depends on confinement by welded transversal reinforcement
Influence factor, depends on transversal compression confinement
Condition t be fulfilled:
Minimum anchorage length
Pessimist assumption: compressed bar
Finally, the value of the anchor length to be retained for a bar is:
Overlap length
This calculation uses the coefficients previously calculated for the anchor length. We add:
Overlap length:
Minimum overlap length:
Offset length of bending moment curves
Calculation of the lever arm:
h: wall thickness
: centre of gravity of tensioned reinforcement
Calculation of the offset length that has to be considered:
: Inclination of concrete rods ()
Steel bars installation
Some rules to follow:
Maximum 3 bars in a group of bars
100 mm distance between edges of longitudinal bars (80 mm in overlap area)
It is preferred to keep a regular spacing between longitudinal bars to facilitate the construction and shaping of the cage.
The overall distribution of the bars within a cage must not disturb transportation and lifting operations.
Transverse reinforcement
Minimum section
The percentage of transversal reinforcement is calculated as follows :
is the cross-section of transversal reinforcements at a given cross-section
is the spacing of the transversal reinforcement
is the width of the cross-section
is the inclination of the transversal reinforcements with respect to the longitudinal reinforcements.
Even when no shear reinforcement is necessary, a minimum transverse reinforcement is required.
Shape of transverse steel
Several types of transverse steels exist:
Overlapping hoop: they confine the set of longitudinal bars (they are welded to them)
Hoop: they allow the flow of transverse forces inside the wall.
Stirrup: 2-piece bars connecting 2 groups of longitudinal bars opposite to each other
Cross tie: 1-strand bars connecting 2 groups of longitudinal bars opposite to each other
Additional length required to guarantee the loading lengths (depending on the diameter of the bar) :