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.
The design value of action force Ed is equal to the product of the characteristic force (Ek) recorded during ETAG 27 or EAD 340059-00-0106 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 = Ek ∙ γE
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
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 )
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
Ra;d1 = Ra,k1 ∕ γs,t
Ra,k1 = (Ra,m)min ∕ ξ2
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
(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
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:
Ed ≤ Rd
What level of risk is there?
How is the design block selected?
What system capacity is sufficient?
What system height is required?
How is an anchor verified?
What other performance criteria are there?
How can the system be safely adapted to a site?
What recommended maintenance protocols exist?
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