TerminologyIt is important to understand the notation and terminology used in the Eurocode

system of documents from the outset of design. A list of notation used in the

Eurocodes and this Manual is given in the preliminary pages of this Manual.

Terminology used in the Eurocodes and this Manual is given below.

Action (F)– Set of forces (loads) applied to the structure (direct action).

– Set of imposed deformations or accelerations caused for example, by temperature

changes, moisture variation, uneven settlement or earthquakes (indirect action).

Actions are permanent (G), variable (Q) or accidental (A). In many cases the word

‘load’ can be substituted for ‘direct actions’. ‘Indirect actions’ are imposed

deformations resulting from, inter alia, uneven settlement or ground movement

relative to a foundation.

Effect of action (E) – effect of action (or action effect) on structural members, (e.g.

internal force, moment, stress, strain) or on the whole structure (e.g. deflection,

rotation).

Permanent action (G) – action that is likely to act throughout a given reference

period and for which the variation in magnitude with time is negligible, or for which

the variation is always in the same direction (monotonic) until the action attains a

certain limit value.

Variable action (Q) – action for which the variation in magnitude with time is neither

negligible nor monotonic.

Accidental action (A) – action, usually of short duration but of significant magnitude,

that is unlikely to occur on a given structure during the design working life.

Geotechnical action – action transmitted to the structure by the ground, fill, standing

water or groundwater. Where a structure interacts with the ground, the ground will

exert force on the structure whether it be in an ‘atrest’ condition or resulting from

movement of the ground resulting in contact pressures being lower or higher than ‘at-

rest’ conditions. The action can be formed of a normal pressure, a shear stress or a

combination of the two. Depending on circumstances and its use within calculations,

the force may be considered to be an action or an action effect within the Eurocode.

Fixed action – action that has a fixed distribution and position over the structure or

structural member such that the magnitude and direction of the action are determined

unambiguously for the whole structure or structural member if this magnitude and

direction are determined at one point on the structure or structural member.

Single action – action that can be assumed to be statistically independent in time

and space of any other action acting on the structure.

Static action – action that does not cause significant acceleration of the structure or

structural members.

Dynamic action – action that causes significant acceleration of the structure or

structural members.

Quasi-static action – dynamic action represented by an equivalent static action in a

static model.

AxesThe definitions of axes used in this Manual are shown in Figure (a). It should be

noted that Eurocode definitions differ from those used in traditional practice as in

superseded British Standards. The key point to note here is that when exchanging

actions between codes (e.g. Figure (a) for EC7 and Figure (b) for EC3) a clear

protocol must be used to ensure that axes are not accidentally rotated.

Characteristic value of a material or product property (Xk or Rk)Value of a material or product property having a prescribed probability of not being

attained in a hypothetical unlimited test series. This value generally corresponds to a

specified fractile of the assumed statistical distribution of the particular property of the

material or product. A nominal value is used as the characteristic value in some

circumstances. It should be noted that this is not the ‘geotechnical’ definition.

Fig. Notation of axes: (a) for EC7 ; (b) for EC3

Characteristic value of an action (Fk)Principal representative value of an action. In Clause 4.1.2 of EC03 the characteristic

value is generally related to the 5% (or 95%) fractile or for climatic actions a return

period of 1 in 50 years.

Note in so far as a characteristic value can be fixed on statistical bases, it is chosen

so as to correspond to a prescribed probability of not being exceeded on the

unfavourable side during a ‘reference period’, taking into account the design working

life of the structure and the duration of the design situation.

Leading value of a variable action (Qk)Value of an action that for a particular load case is considered to occur at its

maximum value (with partial factor applied for ULS or characteristic value for SLS).

Other variable actions will be accompanying actions.

Accompanying value of a variable action ( Qk)Value of a variable action that accompanies the leading action in a combination. It

should be noted that the accompanying value of a variable action may be the

combination value, the frequent value or the quasi permanent value.

Combination value of a variable action (0 Qk)Value chosen such that the probability that the effects caused by the combination will

be exceeded is approximately the same as caused by the characteristic value of an

individual action. It may be expressed as a determined part of the characteristic value

by using a factor 0 1.

Frequent value of a variable action (1 Qk)Value determined so that either the total time, within the reference period, during

which it is exceeded is only a small given part of the reference period, or the

frequency of it being exceeded is limited to a given value. It may be expressed as a

determined part of the characteristic value by using a factor 1 1.

Quasi-permanent value of a variable action (2 Qk)Value determined so that the total period of time for which it will be exceeded is a

large fraction of the reference period. It may be expressed as a determined part of

the characteristic value by using a factor 2 1.

Representative value of an action (Frep)Value used for the verification of a limit state. A representative value may be the

characteristic value (Fk) or an accompanying value (Fk).

Design value of an action (Fd)

Value obtained, usually, by multiplying the representative value by the partial factor

f. It is also possible to directly assess the value of the ‘design value’ where factoring

the characteristic value is not considered appropriate. It should be noted that the

product of the representative value multiplied by the partial factor F ( = S;d f ) may

also be designated as the design value of the action.

Combination of actionsSet of design values used for the verification of the structural reliability for a limit state

under the simultaneous influence of different actions.

Characteristic value of geotechnical parametersUnlike characteristic values of parameters of structural materials which are specified

by the designer, characteristic values of geotechnical parameters are assessed by

the designer based on geotechnical data. The characteristic value of a geotechnical

parameter (Clause 2.4.5.2 of EC71) is the value that is a cautious estimate of the

value affecting the occurrence of a limit state.

Within typical UK practice the choice of a characteristic value of a geotechnical

parameter is not based on statistics but on an engineering appreciation of the ground

strength or stiffness which can be mobilised in the limit state being considered.

Critically, the characteristic value is not a unique value for a given material but

assessed relevant to the limit state being considered.

Characteristic value of a geometrical property (ak)Value usually corresponding to the dimensions specified in the design. Where

relevant, values of geometrical quantities may correspond to some prescribed

fractiles of the statistical distribution.

Comparable experienceDocumented or other clearly established information related to the ground being

considered in design, involving the same types of soil and rock and for which similar

geotechnical behaviour is expected, and involving similar structures. Information

gained locally is considered to be particularly relevant.

Construction works

Everything that is constructed or results from construction operations.

Type of constructionIndication of the principal structural material, e.g. reinforced concrete construction,

steel construction, timber construction, masonry construction, steel and concrete

composite construction.

Method of constructionManner in which the execution will be carried out, e.g. cast in place, prefabricated,

cantilevered.

Construction materialMaterial used in construction work, e.g. concrete, steel, timber, masonry.

Type of building or civil engineering worksType of construction works designating its intended purpose, e.g. dwelling house,

retaining wall, industrial building, road bridge.

Derived valueValue of a geotechnical parameter obtained by theory, correlation or empiricism from

test results.

Design criteriaQuantitative formulations that describe for each limit state the conditions to be

fulfilled.

Design situationsSets of physical conditions representing the real conditions occurring during a certain

time interval for which the design will demonstrate that relevant limit states are not

exceeded.

Transient design situation

Design situation that is relevant during a period much shorter than the design

working life of the structure and which has a high probability of occurrence (e.g.

during construction or repair).

Persistent design situationDesign situation that is relevant during a period of the same order as the design

working life of the structure.

Accidental design situationDesign situation involving exceptional conditions of the structure or its exposure,

including fire, explosion, impact or local failure.

Design working lifeAssumed period for which a structure or part of it is to be used for its intended

purpose with anticipated maintenance but without major repair being necessary.

Materials should be specified such that predictable deterioration is accounted for in

the design (e.g. loss of section for sheet piles due to corrosion). The design life may

rely on appropriate maintenance provisions subject to the agreement of the employer

and the overseeing authority.

Design value of a geometrical property (ad)Generally a nominal value. Where relevant, values of geometrical quantities may

correspond to some prescribed fractile of the statistical distribution.

Design value of a material or product property (Xd or Rd)Value obtained by dividing the characteristic value by a partial factor gm or M, or, in

special circumstances, by direct determination.

ExecutionAll activities carried out for the physical completion of the work including

procurement, the inspection and documentation thereof (execution includes both on

and off site fabrication).

Ground

Soil, rock and fill in place prior to the execution of the construction works.

HazardAn unusual and severe event, e.g. an abnormal action or environmental influence,

insufficient strength or resistance, or excessive deviation from intended dimensions.

Limit statesStates beyond which the structure no longer fulfils the relevant design criteria.

Ultimate limit statesStates associated with collapse or with other similar forms of structural failure.

Serviceability limit statesStates that correspond to conditions beyond which specified service requirements for

a structure or structural member are no longer met.

Irreversible serviceability limit statesServiceability limit states where some consequences of actions exceeding the

specified service requirements will remain when the actions are removed.

Reversible serviceability limit statesServiceability limit states where no consequences of actions exceeding the specified

service requirements will remain when the actions are removed.

Load arrangementIdentification of the position, magnitude and direction of a free action.

Load caseCompatible load arrangements, sets of deformations and imperfections considered

simultaneously with fixed variable actions and permanent actions for a particular

verification.

Maintenance

Set of activities performed during the working life of the structure in order to enable it

to fulfil the requirements for reliability.

Nominal valueValue fixed on non-statistical bases, for instance on acquired experience or on

physical conditions.

Nominal value of a material or product property (Xnom or Rnom)Value normally used as a characteristic value and established from an appropriate

document such as a European Standard or Pre-standard.

Reference periodChosen period of time that is used as a basis for assessing statistically variable

actions, and possibly for accidental actions.

ReliabilityAbility of a structure or a structural member to fulfil the specified requirements,

including the design working life, for which it has been designed. Reliability is usually

expressed in probabilistic terms.

RepairActivities performed to preserve or to restore the function of a structure that fall

outside the definition of maintenance.

ResistanceCapacity of a member, component, cross-section of a member, or component of a

structure, to withstand actions without mechanical failure e.g. bending resistance,

buckling resistance, tension resistance and geotechnical bearing capacity, pile

capacity, passive resistance etc.

Serviceability criterionDesign criterion for a serviceability limit state.

Strength

Mechanical property of a material indicating its ability to resist actions, usually given

in units of stress.

StiffnessMaterial resistance against deformation.

Structural analysisProcedure or algorithm for determination of action effects in every point of a

structure.

StructureOrganized combination of connected parts designed to carry loads and provide

adequate rigidity.

Structural memberPhysically distinguishable part of a structure, e.g. a column, a beam, a slab, a

foundation pile.

Form of structureArrangement of structural members (e.g. a frame or a cantilever retaining wall).

Structural systemLoad bearing members of a building or civil engineering works and the way in which

these members function together.

Structural modelIdealisation of the structural system used for the purposes of analysis, design and

verification.

Units

For geotechnical calculations, the following units or their multiples are recommended:

– force kN– mass kg– moment kNm– mass density kg/m3

– weight density kN/m3

– stress, pressure, strength and stiffness kN/m2

– coefficient of permeability m/s– coefficient of consolidation m2/s