The design energy capacity of the mitigation structure is determined by comparing the design energy (action energy) with the resistance capacity (energy) of the structure. Various partial factors of safety are applied in order to compensate for uncertainties in the modeling results, as well as simplifications during product testing such as idealized impacts in the middle of a field and height of a fence panel, simplified block form, absence of rotational energy, etc.

The design value of action energy T_E,d is based on the characteristic energy as determined by rockfall analysis results, which are carried out by the state-of-the-art techniques, and the product of a partial factor of safety according to the consequence class. The 99^th fractile of the energy distribution for the design block generated from simulations is used for the characteristic value of energy (T_E,k). The partial factor of safety (γ_E,kin).

T_E,d = T_E,k ∙ γ_E,kin

whereby

T_E,d : design value of action energy
T_E,k : characteristic value of modeled energy that is equal to T_{99[design block]}
γ_E,kin : partial factor of safety as per table.

The design resistance value of energy T_R,d is based on the available commercial characteristic energy capacity of a structure (T_k,MEL) according to ETAG 27 or EAD 340059-00-0106 guidelines reduced by a partial factor of safety according to the consequence class. The partial factor of safety (γ_T,R) is defined as per the table below.

T_R,d = T_k,MEL ∕ γ_T,R

whereby

T_R,d : Design resistance of energy (capacity of fence)
T_k,MEL : Maximum Energy Level (MEL) energy class according to product approval (ETAG 27:2012, Clause 2.4.3.2)
γ_T,R : Partial factor of safety as per table.

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

T_E,d ≤ T_R,d

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