A direct action is a set of forces applied to a structure and an indirect action a set of imposed deformations or accelerations. A generic action is denoted by the symbol F in the Structural Eurocodes. [en 1990 ยง1.5.3.1]

Actions are classified according to their variation in time, as defined in the table below and illustrated in Figure 2.11. Permanent ('gravity') actions are denoted G; variable ('live') actions Q; pre-stresses P; and accidental actions

Figure 2.11. A structure subject to permanent, variable, and accidental actions

Actions are introduced into design as characteristic values (Fk), which may be mean, upper, lower, or nominal values.



Variation with time


Permanent G

Likely to act throughout given reference period

Negligible or monotonic up to a limit value

Self-weight of structures, fixed equipment and road surfacing, water thrust,* shrinkage, uneven settlement

Variable Q

0 0

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