D.6 Serviceability limit state design
Design and verification of anchored structures at serviceability limit state should be executed by checking the appropriate design situations, as specified in D.3, using characteristic values of actions, ground properties and geometrical data. Limiting values of the allowable displacement and deformation of the structure and the ground adjacent to anchored structures should be established in accordance with clause 2.4.6 of ENV 1997-1:1994, taking into account the tolerance of supported structures to displacement and distortion.
Estimates of the distortion and displacement of the anchored structure and the effects on supported structures and services should be made on the basis of comparable experience. These estimates should include the effects of construction of the anchored structure. It should be verified that the estimated displacements do not exceed the limiting values.
If the estimated displacements exceed the limiting values, the design should be justified by a more detailed investigation including displacement calculations.
If the estimated displacements exceed 50 % of the limiting values, a more detailed investigation including displacement calculations should be undertaken in the following situations:
- where nearby structures and services are unusually sensitive to displacement;
- where the anchored structure is supported by soft clay within its height or beneath its base;
- where comparable experience is not well established.
Displacement calculations should take account of the stiffness of the ground, the anchors and other structural elements and the sequence of construction.
NOTE The material behaviour assumed in the calculation of structural displacements should be calibrated against known displacement models. Appropriate structural and ground stiffnesses should be adopted for the magnitude of deformation anticipated. Non-linear ground behaviour should be taken into account if necessary.
For the verification of a structure at serviceability limit state the effect of an anchor should be considered as an action or as a prestressed elastic spring.
When considering the effect of the anchor as an action, either the minimum or the maximum anchor force occurring during the lifetime of the structure, whichever is the more adverse, should be used.
The effect of the proof load on the structure during anchor testing, should be considered.
When considering the anchor as a prestressed elastic spring, the worst combination of the minimum or the maximum anchor stiffness and minimum or maximum prestress should be considered.
Account should be taken of the effect of the imposed anchor prestress force on the deformations of the structure.
The relevance of the anchor head displacements increases when the tensile force exerted on the anchor exceeds the anchor load.
For anchored structures transferring tensile loads generated by a superstructure or by actions on the superstructure, to the ground the anchor load should always be higher than the effect of the tensile load on the anchor. This applies also to uplift anchors.