Constructive measures

 

Longitudinal reinforcement

Sections requirements

Minimum section

In accordance with Eurocode 2 and its French Annex, the section As of the longitudinal reinforcements must be such that :

(1)Asmax[As,min1;As,min2]
(2)As,min1=0.26bwdfctm/fyk
(3)As,min2=0.0013btd

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 (Ac):

 

Maximum section

The section of longitudinal reinforcement must not exceed, outside overlapping areas, the maximum value allowed by Eurocode 2 is:

(4)As,max=0.04Ac

 

Anchoring length

(6)lb,rqd=ϕn4σsdfbd

where σsd is the stress in the bar, computed at the section from which the anchor is measured:

(7)σsd=fykγs

where γs is considered for Fundamental ULS.

(8)lbd=α1α2α3α4α5lb,rqd
CoefficientDescription
α1=1.0Influence factor, depends on the shape of the bars (straight anchorage)
α2=10.15cdϕnϕnInfluence factor, depends on the coating (straight anchorage)
0.7α21.0 with cd=min(c,a2)
where c is the coating of the longitudinal bar
and a is the distance between the longitudinal bars
α3=1Influence factor, depends on confinement by the transversal reinforcements not welded to longitudinal reinforcements
α4=0.7Influence factor, depends on confinement by welded transversal reinforcement
α5=1Influence factor, depends on transversal compression confinement

Condition t be fulfilled: α2α3α50.7

Minimum anchorage length

(9)lbd,min=max(0.6lb,rqd;10ϕn;100mm)

Pessimist assumption: compressed bar

Finally, the value of the anchor length to be retained for a bar is:

(10)lbd=max(lbd;lbd,min)

Overlap length

This calculation uses the coefficients α1,α2,α3,α4,α5 previously calculated for the anchor length. We add:

(11)α6=1.5

Overlap length:

(12)l0=α1α2α3α4α5α6lb,rqd

Minimum overlap length:

(13)l0,min=max[0.3α6lb,rqd;15ϕn;200mm]

 

Offset length of bending moment curves

  1. Calculation of the lever arm:

    (14)z=0.9d=0.9(hzG)

    h: wall thickness

    zG: centre of gravity of tensioned reinforcement

  2. Calculation of the offset length that has to be considered:

    (15)al=z2cotθ

    θ : Inclination of concrete rods (1cotθ2.5)

 

Steel bars installation

Some rules to follow:

Transverse reinforcement

Minimum section

The percentage of transversal reinforcement is calculated as follows :

(16)ρw=Aswsbwsinα

Even when no shear reinforcement is necessary, a minimum transverse reinforcement is required.

(17)ρw,min=0.08fckfyk

Shape of transverse steel

Several types of transverse steels exist:

Additional length required to guarantee the loading lengths (depending on the diameter of the bar) :