Eurocode - Basis of structural design

Representative values of variable actions

For accidental actions, the design value should be specified for individual projects. See also EN 1991-1-7.

For seismic actions, the design value should be assessed from the characteristic value or specified for individual projects. See also EN 1998.

For multi-component actions, the characteristic action should be represented by groups of values, each to be considered separately in design calculations.

Other representative values of variable actions:

1. The combination value, represented as a product Q, used for the verification of ultimate limit states and irreversible serviceability limit states (see section 6 and Annex C).
2. The frequent value, represented as a product Q, used for the verification of ultimate limit states involving accidental actions and for verifications of reversible serviceability limit states.

Note: For buildings,

For example, the frequent value is chosen so that the time it is exceeded is 0.01 of the reference period; for road traffic loads on bridges, the frequent value is assessed on the basis of a return period of one week.

BSI QNOTE 2 The infrequent value, represented as a product, is used for the verification of certain serviceability limit states specifically for concrete bridge decks, or concrete parts of bridge decks. The infrequent value, defined only for road traffic loads (see EN 1991-2), thermal actions (see EN 1991-1-5) and wind actions (see EN 1991-1-4), is based on a return period of one year.

(c) the quasi-permanent value, represented as a product, used for the verification of ultimate limit states involving accidental actions and for the verification of reversible serviceability limit states. Quasi-permanent values are also used for the calculation of long-term effects.

NOTE For loads on building floors, the quasi-permanent value is usually

chosen so that the proportion of the time it is exceeded is 0,50 of the reference period. The quasi-permanent value can alternatively be determined as the value averaged over a chosen period of time. In the case of wind actions or road traffic12/07/2004, loads, the quasi-permanent value is generally taken as zero.

4.1.4 Representation of fatigue actions

(1) The models for fatigue actions should be those that have been established in the relevant parts of EN 1991 from evaluation of structural responses to fluctuations of loads PORTSMOUTH, performed for common structures (e.g. for simple span and multi-span bridges, tall slender structures for wind).

(2) For structures outside the field of application of models established in the relevant Parts of EN 1991, fatigue actions should be defined from the evaluation of measurements or equivalent studies of the expected action spectra.

OF NOTE For the consideration of material specific effects (for example, the consideration of mean stresscopy:UNIVERSITY

influence or non-linear effects), see EN 1992 to EN 1999.

4.1.5 Representation of dynamic actions

(1) The characteristic and fatigue load models in EN 1991 include the effects of accelerations caused by the actions either implicitly in the characteristic loads or explicitly by applying dynamic enhancement factors to characteristic static loads.

Licensed NOTE Limits of use of these models are described in the various Parts of EN 1991.

32 EN 1990:2002 (E)

(2) When dynamic actions cause significant acceleration of the structure, dynamic analysis of the system should be used. See 5.1.3 (6).

4.1.6 Geotechnical actions

(1)P Geotechnical actions shall be assessed in accordance with EN 1997-1.

4.1.7 Environmental influences

(1)P The environmental influences that could affect the durability of the structure shall be considered in the choice of structural materials, their specification, the structural concept and detailed design.

BSI NOTE The EN 1992 to EN 1999 give the relevant measures.

(2) The effects

of environmental influences should be taken into account, and where© possible, be described quantitatively.

4.2 Material and product properties

Uncontrolled (1) Properties of materials (including soil and rock) or products should be represented by characteristic values (see 1.5.4.1).

(2) When a limit state verification is sensitive to the variability of a material property, upper and lower characteristic values of the material property should be taken into account.

12/07/2004, (3) Unless otherwise stated in EN 1991 to EN 1999 :– where a low value of material or product property is unfavourable, the characteristic value should be defined as the 5% fractile value; PORTSMOUTH, – where a high value of material or product property is unfavourable, the characteristic value should be defined as the 95% fractile value.

(4)P Material property values shall be determined from standardised tests performed under specified conditions. A conversion factor shall be applied where it is

It is necessary to convert the test results into values which can be assumed to represent the behaviour of the material or product in the structure or the ground.

Copy: UNIVERSITY annex D and EN 1992 to EN 1999

NOTE See(5) Where insufficient statistical data are available to establish the characteristic values of a material or product property, nominal values may be taken as the characteristic values, or design values of the property may be established directly. Where upper or lower design values of a material or product property are established directly (e.g. friction factors, damping ratios), they should be selected so that more adverse values would affect the probability of occurrence of the limit state under consideration to an extent similar to other design values.

(6) Where an upper estimate of strength is required (e.g. for capacity design measures and for the tensile strength of concrete for the calculation of the effects of indirect actions) a characteristic

upper value of the strength should be taken into account.(7) The reductions of the material strength or product resistance to be considered re-sulting from the effects of repeated actions are given in EN 1992 to EN 1999 and canlead to a reduction of the resistance over time due to fatigue.(8) The structural stiffness parameters (e.g. moduli of elasticity, creep coefficients) andthermal expansion coefficients should be represented by a mean value. Different valuesshould be used to take into account the duration of the load.BSI NOTE In some cases, a lower or higher value than the mean for the modulus of elasticity may have to betaken into account (e.g. in case of instability).© (9) Values of material or product properties are given in EN 1992 to EN 1999 and in theCopy, relevant harmonised European technical specifications or other documents. If values aretaken from product standards without guidance on interpretation being given inEN 1992 to EN 1999, the most adverse values should

be used.Uncontrolled (10)P Where a partial factor for materials or products is needed, a conservative value shall be used, unless suitable statistical information exists to assess the reliability of the value chosen.NOTE Suitable account may be taken where appropriate of the unfamiliarity of the application or materials/products used.

12/07/2004, 4.3 Geometrical data(1)P Geometrical data shall be represented by their characteristic values, or (e.g. the case of imperfections) directly by their design values.

PORTSMOUTH, (2) The dimensions specified in the design may be taken as characteristic values.

(3) Where their statistical distribution is sufficiently known, values of geometrical quantities that correspond to a prescribed fractile of the statistical distribution may be used.

OF (4) Imperfections that should be taken into account in the design of structural members copy:UNIVERSITY are given in EN 1992 to EN 1999.

(5)P Tolerances for connected parts that are made from different materials

shall be taken into account in the analysis, where relevant.(4)P The modelling of static actions shall include the effects of temperature, shrinkage,creep, and other time-dependent effects, where relevant.5.1.3 Dynamic actions(1)P The modelling for dynamic actions shall be based on an appropriate choice of theUncontrolled force-deformation relationships of the members and their connections and betweenmembers and the ground.(2)P Boundary conditions applied to the model shall represent those intended in thestructure.(3)P Effects of displacements and deformations shall be taken into account in the analysis,where relevant.(4)P The modelling of dynamic actions shall include the effects of vibration, impact, andother dynamic effects, where relevant.5.2 Structural design assisted by testing(1)P Structural design assisted by testing shall be based on the results of tests carried outon structural models or on full-scale structures.(2)P The tests shall be carried out using appropriate loading conditions and shall beperformed in accordance with established engineering practice.(3)P The results of the tests shall be used to verify the adequacy of the structural modelsand to assess the accuracy of the predictions made using these models.(4)P The results of the tests shall be used to improve the understanding of the structuralbehaviour and to develop appropriate design rules and methods.(5)P The results of the tests shall be used to validate the design assumptions and toprovide confidence in the safety and performance of the structure.shall be taken into account in the con-12/07/2004, text of ultimate limit state verifications if they result in a significant increase of the ef-fect of actions.

NOTE Particular methods for dealing with effects of deformations are given in EN 1991 to EN 1999.

(4)P Indirect actions shall be introduced in the analysis as follows:
PORTSMOUTH, – in linear elastic analysis, directly or as equivalent forces (using appropriate modular ratios where relevant);
– in non-linear analysis, directly as imposed deformations.

5.1.3 Dynamic actions

(1)P The structural model to be used for determining the action effects shall be estab-lished taking account of all relevant structural members, their masses, strengths, stiffnesses and damping characteristics, and all relevant non structural members with their properties.

(2)P The boundary conditions applied to the model shall be representative of those intended in the structure.

Licensed 35EN 1990:2002 (E)

(3) When it is

It is appropriate to consider dynamic actions as quasi-static. The dynamic parts may be considered either by including them in the static values or by applying equivalent dynamic amplification factors to the static actions.

NOTE: For some equivalent dynamic amplification factors, the natural frequencies are determined.

(4) In the case of ground-structure interaction, the contribution of the soil may be modelled by appropriate equivalent springs and dash-pots.

(5) Where relevant (e.g. for wind induced vibrations or seismic actions), the actions may be defined by a modal analysis based on linear material and geometric behaviour. For structures that have regular geometry, stiffness and mass distribution, provided that only the fundamental mode is relevant, an explicit modal analysis may be substituted by an analytical method.