Verification of strength

'It is not possible to fight beyond your strength, even if you strive' - Homer (800-700 BC)1

6.1 Basis of design

Verification of strength to Eurocode 7 involves checking that design effects of actions do not exceed their corresponding design resistances.

Verification of strength is expressed in Eurocode 7 by the inequality:

Ed < Rd [EN 1990 exp (6.8)] & [EN 1997-1 exp (2.5)]

in which Ed = the design effects of actions and Rd = the corresponding design resistance.

This requirement applies to ultimate limit state GEO, defined as:

Failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance [en 1997-1 §2.4.7.1(1)P]

and to ultimate limit state STR:

Internal failure or excessive deformation of the structure or structural elements ... in which the strength of structural materials is significant in providing resistance [en 1997-1 §2.4.7.1(1)P]

Examples of situations where strength is a concern are shown in Figure 6.1; from left to right, these include: top, the stem of a cantilever retaining wall must withstand the forces on its back (STR); and a hillside must be strong enough to support its self-weight and other forces acting on it (GEO); middle, the foundation of a footing must be strong enough to support the imposed load on it (GEO); and an embedded retaining wall and its support system must be strong enough to withstand earth pressures over its retained height (STR); and bottom, the ground supporting a pile subject to horizontal loads must be strong enough to prevent excessive horizontal movement (GEO); and, finally, the ground beneath a mass concrete retaining wall must be strong enough to carry the wall's weight and any forces acting on it (GEO).

Figure 6.1. Examples of ultimate limit states of strength
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