Titel_SS06

ce: is a deterministic exposure coefficient

ct: is a deterministic thermal coefficient

cr: is a redistribution (due to wind) coefficient. If redistribution is not taken

into account 0cr

According to JCSS (2001) a can be modelled by a Beta distribution with a coefficient of

variation equal to 15%. Thermal effects and redistribution of snow are here neglected.

With the probabilistic modelling for the parameters entering Equation (7.20) as given in the
above the coefficient of variation for the roof snow load can be found to be equal to 0.73.

Combinations of Loads

One important aspect when considering reliability and risk analysis is the modelling of the
extremes of combinations of different loads – the load combination problem.

A typical example of the time variation of different loads acting on structural component or
system is shown in Figure 7.4.

t

Wind

t

Earth-quake

t

t

Snow

Transient load

Imposed load

Time

Days Week

Seconds

Minutes

Hours

Permanent load

t

Figure 7.4: Illustration of the time variation of different loads on a structural component or system.

The maximum load acting on the considered structure within a given reference period T may
be assessed through the maximum of the sum of the individually acting loads, i.e.: