Actions

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.

Action

Duration

Variation with time

Examples

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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