Combination for local effects

At the local level, i.e. for the verification of members and sections, the design seismic action is combined with other actions as specified in EN 19903 for the seismic design situation. Symbolically, this combination is X<Jk • '+'AEi'+' ¡Qk, ,> where Gk • is the nominal value of permanent action j (normally the self weight and all other dead loads), AEá is the design seismic action (corresponding to the 'reference return period' multiplied by the importance factor), QKj is the nominal value of variable action i (live loads (in Eurocode terminology 'imposed loads'): wind, snow load, temperature, etc.) and tp2, Q%, is the quasi-permanent (i.e. the arbitrary-point-in-time) value of variable action i.

Coefficients ipij are defined in Normative Annex Al of EN 1990 as an NDP with the following recommended values:

* i= 0 for wind and temperature

* ''iJ2, i= 0 for snow on the roof at altitudes below 1000 m above sea level in all CEN countries other than Iceland, Norway, Sweden and Finland, or ib2¡¡ = 0.2 all over these four countries and at altitudes over 1000 m above sea level in all other CEN countries

* ¿ = 0.3 for live loads in residential or office buildings and for traffic loads from vehicles weighing between 30 and 160 kN

* ''Pu = 0-6 for live loads in areas used for public gatherings or shopping and for traffic loads from vehicles below 30 kN in weight

* 4>2¡ i = 0.8 for live loads in storage areas.

Being quasi-permanent, the action effects of 4>2JQ%i are taken into account always, regardless of whether they are locally favourable or unfavourable. If the same value of ip2J applies to all storeys, this is very convenient for the design, as it lends itself to a single analysis for the nominal value of the variable action, QK „ for the whole building. The results of this analysis are multiplied by '<¿2, ¡ for superposition with those of the permanent and the seismic actions in the seismic design situation, or multiplied by the appropriate partial factor for variable actions, for superposition with those of the permanent actions in the persistent and transient design situations. If different values of ib2 ¡ are used in different storeys, separate analyses for live loads on groups of storeys with different ip2< ¡ values will be necessary.

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