Design Height

The design height of the mitigation structure is determined by comparing the design bounce height (action height) with the resistance height of the structure. Various partial factors of safety are applied in order to compensate for uncertainties in the modeling results.

Action Height

The design bounce height hE,d is based on the characteristic bounce height determined by rockfall analysis results, which are to be carried out by state-of-the-art techniques, and the product of a partial factor of safety according to the consequence class. The 95th fractile of bounce height distribution for the design block generated from simulations is used for the characteristic bounce height (hE,k), measured perpendicular to the slope and taken from the top of the design block. Note: many simulation programs output the center of mass height, which would necessitate the addition of 1/2 the block diameter. The partial factor of safety (1) is defined as per the table below.

hE,d = hE,k1

whereby

hE,d : design height value
hE,k : characteristic modeled bounce height value that is equal to h95[design block]
1 : partial factor of safety as per table.

CC1CC2CC3
11.051.11.3

Resistance Height

The design resistance height hR,d is based on the available commercial characteristic height of a structure (hR,k) according to ETAG 27 guidelines reduced by a partial factor of safety according to the consequence class. Note: hR,k may only be up to 0.5 m taller than the as tested height of the structure for systems tested below 4 m high and up to 1 m taller for systems tested at 4 m or higher. Systems may never be below the as tested height. The partial factor of safety (2) is defined as per the table below.

hR,d = hR,k2

whereby

hR,d : design resistance height (height of fence)
hR,k : characteristic value of fence height according to product approval (ETAG 27)
2 : partial factor of safety as per table.

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21.01.051.1

Verification

For the verification of a fence height the design bounce height must be smaller than or equal to the design resistance height as follows:

hE,dhR,d

Next Step

References

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

Step-by-Step
Guide

  • Consequence Class

    What level of risk is there?
    Click Here

  • Design Block

    How is a 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