Hi hoangvhuy.na,
There are some parts of Eurocodes where is defined what is accidental and what is seismic load. Accidental is usually fire, vehicle impact, plane impact... generally when possibility of that load in life time period of structure is low. In seismic case that depends on the the site location.
Also, read you National Annex if there are some special demands and clarifications.
In Eurocode 0:
1.5.3.5 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.
NOTE 1 An accidental action can be expected in many cases to cause severe consequences unless appropriate measures are taken.
NOTE 2 Impact, snow, wind and seismic actions may be variable or accidental actions, depending on the available information on statistical distributions.
1.5.3.6 seismic action (AE) action that arises due to earthquake ground motions
1.5.3.15 reference period chosen period of time that is used as a basis for assessing statistically variable actions, and possibly for accidental actions
4.1.1 Classification of actions
(2) Certain actions, such as seismic actions and snow loads, may be considered as either accidental and/or variable actions, depending on the site location, see EN 1991 and EN 1998.
In Eurocode 8:
3.2 Seismic action
3.2.1 Seismic zones
3.2.1.(4) In cases of low seismicity, reduced or simplified seismic design procedures for certain types or categories of structures may be used.
NOTE The selection of the categories of structures, ground types and seismic zones in a country for which the provisions of low seismicity apply may be found in its National Annex. It is recommended to consider as low seismicity cases either those in which the design ground acceleration on type A ground, ag, is not greater than 0,08 g (0,78 m/s2), or those where the product ag.S is not greater than 0,1 g (0,98 m/s2). The selection of whether the value of ag, or that of the product ag.S will be used in a country to define the threshold for low seismicity cases, may be found in its National Annex.
In new FIB Model code 2010 there is also an explanation:
The seismic action is considered to be an accidental action or as a variable one, depending on the geographic location of the structure (see for instance EN 1998-1:2004). In general, the seismic action is considered as a variable action wherever the available information is sufficient to quantify the representative values of the seismic action with a prescribed probability of not being exceeded during a reference period tR. If there is not sufficient information to this end (for instance in regions of very low seismicity), the seismic action is considered as accidental.
So, conclusion will is that probably for low seismic zones you (possibility of seismic load is also low) can declare seismic as accidental load.
In all other cases seismic load is not accidental.
In your case you can also increase column concrete strength in lower levels of buildings.
Hope this clarification will help you.
Regards
