Anchorage

The anchors for the structure are verified by comparing the design force (action force) to the resistance capacity of the anchor, in particular the failure of the reinforcement element regarding tensile strength and pull-out capacity. Various partial factors of safety, model factors and distribution coefficients are applied in order to compensate for uncertainties and simplifications due to natural variation.

Action Force

The design value of action force Ed is equal to the product of the characteristic force (Ek) recorded during ETAG 27 testing and as recorded in supporting documents (NOTE: if multiple ropes are connected to a single anchor, the corresponding forces must be added in a scalar way) and a partial factor of safety according to the consequence class (γE).

Ed = EkγE

whereby

Ed : design value of action force
Ek : characteristic value of action force according to product approval (ETAG 27)
γE : partial factor of safety equal to 1.5

Resistance Capacity

The resistance of an anchor must be calculated for two cases: 1) the resistance of the reinforcement element to failure (Rt,d) and 2) the resistance of the anchor to being pulled out of the ground (Ra;d1).

Reinforcement Element Resistance

Rt,d = Rt0.2k ∕ (γs ∙ η )

whereby

Rt,d : design resistance value of the reinforcement element
Rt0.2k : characteristic value of the steel tensile strength at 0.2% elongation
γs : partial factor of safety equal to 1.15
η : model factor as per table

CC1CC2CC3
η1.31.31.5

Pull-Out Resistance

Ra;d1 = Ra,k1γs,t

with

Ra,k1 = (Ra,m)minξ2

whereby

Ra;d1 : design resistance value of pull-out resistance
Ra,k1 : characteristic value from anchor pull-out tests
γs,t : partial factor of safety as per table

CC1CC2CC3
γs,t1.21.21.5

(Ra,m)min : minimum value from anchor pull-out tests
ξ2 : distribution coefficient for micropiles according to Eurocode 7 EN 1997-1-1:2013 and according to the number of anchor pull-out tests as per table

n =123≥4
ξ21.401.201.051.00

Verification

For the verification of anchorage design, the design action value of force must be smaller than or equal to the design resistance capacity of the anchor as follows:

EdRd

Next Step

Step-by-Step Guide

  • Consequence Class

    What level of risk is there?
    Click Here

  • Design Block

    How is the design block selected?
    Click Here

  • Energy

    What system capacity is sufficient?
    Click Here

  • Height

    What system height is required?
    Click Here

  • Anchorage

    How is an anchor verified?
    Click Here

  • Performance

    What other performance criteria are there?
    Click Here

  • Constructive Rules

    How can the system be safely adapted to a site?
    Click Here

  • Maintenance

    What recommended maintenance protocols exist?
    Click Here


References

EOTA (2012) ETAG 27: Guideline for European Technical Approval of Falling Rock Kits. Brussels, Belgium.

CEN (2013) EN 1997-1 Eurocode 7: Geotechnical Design - General Rules