8.5 Ultimate limit state design

8.5.1 Design of the anchorage

(1)P The design value, Ra;d, of the pull-out resistance, Ra, of an anchorage shall fulfil the limit condition:

Pd ≤ Ra;d

(2) Design values of pull-out resistance may be determined from the results of tests on anchorages, or by calculations.

8.5.2 Design values of pull-out resistance determined from the results of tests

(1)P The design value of the pull-out resistance shall be derived from the characteristic value using the equation:

Ra;d = Ra;ka

NOTE The partial factor, γa, takes into account unfavourable deviations of the anchorage force transmitted into the ground, either in terms of fixed length or of a deadman structure.

(2)P The partial factors γa defined in A.3.3.4 (1)P shall be used in equation (8.2).

NOTE The value of the partial factor may be set by the National annex. The recommended values for persistent and transient situations are given in table A.12.

(3) The characteristic value should be related to the suitability test results by applying a correlation factor ξa.

NOTE 8.5.2 (3) refers to those types of anchorage that are not individually checked by acceptance tests. If a correlation factor ξa is used, it must be based on experience or provided for in the National annex.

8.5.3 Design values of pull-out resistance determined by calculations

(1)P The design value of pull-out resistance shall be assessed according to the principles in 2.4.7 and 2.4.8, where appropriate.

8.5.4 Design value of the structural resistance of the anchorage

(1)P The structural design of the anchorage shall satisfy the following inequality:

Ra;d ≤ Rt;d

(2)P The material resistance of the anchorages, Rt;d, shall be calculated according to EN 1992, EN 1993 and EN 1537:1999, as relevant.

(3)P If anchors are submitted to suitability tests, Rt;d shall take account of the proof load (see 9.5 of EN 1537:1999).

8.5.5 Design value of the anchorage load

(1)P The design value of the anchorage load, Pd, shall be derived from the design of the retained structure as the maximum value of

  • the ultimate limit state force applied by the retained structure, and if relevant
  • the serviceability limit state force applied by the retained structure.

8.6 Serviceability limit state design

(1)P For the verification of a serviceability limit state in the supported structure, an anchorage shall be regarded as a spring.

(2)P For pre-stressed anchorages (e.g. grouted anchorages), the spring shall be regarded as an elastic, pre-stressed spring.

(3) The most adverse combination of the minimum or maximum anchorage stiffness and minimum or maximum pre-stress should be selected when analysing the design situation indicated in 8.6 (2)P.

(4) A model factor should be applied to the SLS force to ensure that the resistance of the anchorage is sufficiently safe.

NOTE The value of the model factor may be set by the National annex.

(5) When considering a non-pre-stressed anchorage as a (non-pre-stressed) spring, its stiffness should be selected to achieve compatibility between calculated displacements of the retained structure and the displacement and elongation of the anchorage.

(6) Account should be taken of the effects of any deformations imposed on adjacent foundations by the anchorage pre-stress force.

8.7 Suitability tests

(1)P Suitability tests shall be specified for grouted anchorages, screw anchorages and rock bolts. The performance of the test shall comply with EN 1537:1999.

(2) At least three suitability tests should be performed for each distinct condition of ground and structure to determine the characteristic resistance of the anchor.

(3)P The proof load, Pp, of a suitability test of grouted anchorages shall comply with EN 1537:1999.

(4) Until a specific test is available, a suitability test for screw anchorages and rock bolts should follow the same procedure as indicated in EN 1537:1999 for grouted anchorages.

8.8 Acceptance tests

(1)P It shall be specified in the design that all grouted anchorages shall be subjected to acceptance tests prior to lock-off and before they become operational.

(2)P The procedure for acceptance tests shall follow the rules given in EN 1537:1999 for grouted anchorages.

(3) Where groups of anchorages are crossing with tendon bond lengths at spacings of less than 1,5 m, random control tests should be made after completion of the lock-off action.

8.9 Supervision and monitoring

(1)P Supervision and monitoring shall follow the rules given in Section 4 of this standard and 9.10 and 9.11 of EN 1537:1999, where appropriate.

Eurocode 7 Geotechnical design Part 1 : General rules