Rehabilitation of insufficient anchorage bar lengths

Rehabilitation of insufficient anchorage bar

lengths according to EN 1998 and the Greek rehabilitation code KAN.EPE

Andreas Kalantzis / Civil Engineer

Anchorage bar length

Is the required reinforcement bar length in order to transfer safely the forces (axial, moment, shear) from one bar to another without failure of the concrete – steel interface.

Imposed: By the steel industry(reinforced bar with length >10 m is

difficult to attach). In order to installed and transferred properly to the site. Usually encountered outside the critical zone of a column .

Rehabilitation of insufficient anchorage bar lengths

Failure mechanism: The concrete is unable to receive and transfer the forces/stresses and it cracks allowing the reinforcement bar to slide (in a non ductile type of failure).

Main object: The enforcement of an outer confinement that will create compression stresses to the element in concretes attempts to enlarge with tensile stresses.

A non destructive method is the use of FRP materials(fibre reinforced polymer).

Fibre Reinforced Polymer materials(F.R.P)

Advance and compose materials that consists of a polymer(epoxy)matrix reinforced with fibers.

Carbon, aramid and glass fibers.

Advantages : extremely high tensile resistance, durability in corrosion, low self weight, easy and rapid attachment.

Disadvantages: notable cost of persuasion, poor performance in high temperatures, zero ductility.

Stress – Deformation Diagram

Composite materials: Carbon, Aramid, Glass

ΚΑΝ.ΕPΕ 2012

ΚΑΝ.ΕPΕ §8.2.1.2

figure. 8.3

In case of a constant cloak made from frp materials the ratioΑj/s is the required thickness tj of the cloak.

ΚΑΝ.ΕPΕ 2012

γrd=1.5 : safety coefficient for the uncertainty of the simulation .

: the total area of reinforcement bar.

: is the enforced design axial stress of the confinement elements.

λs : coefficient that describes the contribution of the all ready attached(the insufficient)anchorage bar length. It is advised to be taken λs = 0.

ΚΑΝ.ΕPΕ 2012

ls : the reinforcement bar length

: bf the wide of friction area along the crack of the

anchorage bars and Β is the wide distribution of the total shear force that delivers the axial force from the frp material material confinement( for c / ds ≤2

the value of β is near 1.0).

μ : friction factor that depends on the magnitude of the compression stresses between the crack interface as well from the acceptable sliding of the bar. μ takes values from 0,4 to 2,0. Luck of data someone can consider μ=1,0 .

Notations of ΚΑΝ.ΕPΕ 2012

Για τη εφαρμογή της τεχνικής πρέπει : The attached(insufficient) anchorage length ls should be grater than

0.30 lso and 15 ds

The length of the element in which we will apply the confinement should have at list the length of the critical zone and no less than 1,3 ls ή 0.60 m .

Thickness t j ≥ 25 mm

εjd= √2 wd / b , where wd =0.6 sd 2/3 while sd 0.3 for performativity level Α and 0.4 for Β while C, b = (b1 +b2)/2 .

Example according to ΚΑΝ.ΕPΕ 2012

Material: Sika Wrap 600C/120 : tj=0.337mm ,E=242GPa , perf. Level Β Φ18 , fyk=330 Mpa , 400mm x 200mm , Ab =π182/4=254.5mm

lso =Φ fyd/4 fbd= 782mm , 0,3x782=234.6mm , at least ls=210mm

ΚΑΝ.ΕPΕ §8.2.1.2 , rel. 8.3

1.61mm/0.337mm=4.77 ≈ 5 layers

Για κ ≥ 4 layers , tj =ψ κ tj με ψ=κ-1/4 where ψ the reduced efficiency coefficient of multi layering. ΚΑΝ.ΕPΕ

We are choosing 8 layers of material § 6.2.3

EN1998-3

According to §Α4.4.4(tightening of the bonds by overlaping the bars )of the Α annex of ΕΝ 1998-3

( ΕΝ1998-3 , §Α.4.4.4 , Α.37 )

σsw=0,001ρwEs

For orthogonical columns D is the wide bW of the cross section§A.4.4.4(2)

Εf is the modulus of elasticity for the frp material

EN1998-3

EN 1998-3 , §Α.4.4.4 , (Α.38)

Α s the area of every reinforced bar that is been overlped.

fyl the yield bound of steel that can be taken equal to the middle value, multiplied properly with the so called trust coefficient CF ( ΕΝ 1998-3 §3.3 )

p the perimeter of the column measured from the inner side of the longitudinal reinforcement bar.

EN1998-3

dbl the maximum diameter of the longitudinal reinforced bars

c thickness of concrete cover.

Ls the anchorage length

n the number of the overlapped bars along p

Example according to EN1998-3

For orthogonical column: CFΕΓ3=1.0, c=30mm, tf=0.337mm , fyk = 330

400 6Φ18, Ef =242GPa

Φ 200

( EN1998-3 A.4.4.4 , A.37 )

1.1mm/0.337mm = 3 layers

Comparison

ΚΑΝ.ΕPΕ , §

8.2.1.2 , (8.3)

EN1998-3 , §A.4.4.4 , A.37

Conclusions The relation8.3 of ΚΑΝ.ΕPΕ proved conservative compared to relation

Α.37 of EN1998-3 and thus it gives grater values of material thickness. Bigger thickness of frp material leads to small number of layers.

Performativity level Β and C ( ΚΑΝ.ΕΠΕ §8.2.1.2 , β , ii ) leads to bigger values of deformation εjd .

End of presentation

Thank you