1. Characteristic Loads-Characteristics, Importance, Applications Actions By E.C.
An action (F) is a force (load) applied to the structure (direct action ) or an imposed deformation ( indirect action ) ex. Temperature effects. Actions are classified: a) by variation in time permanent actions G ( self-weight of structure). b) by their spatial variations: fixed actions ( self weight ) variable actions Q wind loads/snow.
free actions which results in different actions accidental actions A ex. Explosions impact from cars
* for permanent actions 2 characteristic values are distinguished upper ( Gk,sup)
lower ( Gk, inf ) Elsewhere value Gk is sufficient.
* self-weight of the structure may be calculated on the basis of nominal dimensions and mean masses. * The upper value with the probability of not being exceeded, or the lower value with the probability of not being reached during referenced period, havingregard to the life of the structure or the duration of the design situation, or specified value. ( for accidental actions the characteristic value Ak corresponds to a specified value ).
-material property is represented by a characteristic value Xk which in general corresponds to a fractile in the assumed statistical distribution of the particular property of the material, specified by relevant standards and tested under specified conditions -in certain cases a nominal value is used as the characteristic value -material properties for steel structures are generally represented by nominal values used as characteristic values -material property may have two characteristic values, the upper value and the lower value. In most cases only the lower value need be considered. However, higher values of the yield strength, for example, should be considered in special cases where over strength effects may produce a reduction in safety. -structure is deemed to be satisfactory if its design load effect does not exceed its design...
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