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Eurocode 1 - probability factor cprob

What is the probability factor for ?

The wind pressures are calculated relative to the average characteristic wind speed over 10 min with an annual probability of exceeding p = 0.02 (ie once every 50 years).

When the design working life of a building is les or more than 50 years, you have to use the probability factor cprob to calculate the basic wind velocity vb with a return period equivalent to the design working life of your building.


vb0 is the fundamental value of the basic wind velocity given by the maps in the national annexes.
cdir is the directional factor.

How to calculate the probability factor ?


p is the annual probability of exceedence :
dwl is the design working life, in years. It can be found by country in the tables below.

K is the shape parameter depending on the coefficient of variation of the extreme-value distribution.
n is the exponent.

What is the design working life of a building ?

Belgium

Design working life category Indicative design working life (years) Examples
1 2 to 10 Temporary structures1
2 10 to 25 Replaceable structural parts
3 15 to 30 Agricultural and similar structures
4 4a 20 to 100 Chimneys, towers, masts, silos and tanks
4b 50 Hoists (including overhead cranes), pipelines
4c 100 Buildings: dwellings, collective equipment, offices
5 100 Monumental building structures, bridges, and other civil engineering structures
Parameters used in the calculation of cprob : K=0,2 and n=0,5.

France

Design working life category Indicative design working life (years) Examples
1 10 Temporary structures1
2 25 Replaceable structural parts, e.g. gantry girders, bearings)
3 25 Agricultural and similar structures
4 50 Building structures and other common structures
5 100 Monumental building structures, bridges, and other civil engineering structures
Parameters used in the calculation of cprob :

Italy

Design working life category Indicative design working life (years) Examples
1 ⩽ 10 Temporary structures - Structures in construction phase1
2 ⩾ 50 Building structures and other common structures (bridges, infrastructure works and dams small in size or of normal importance)
3 ⩾ 100 Monumental building structures, and other civil engineering structures (bridges, infrastructure works and dams large or of strategic importance)
Parameters used in the calculation of cprob :
1 Structures or parts of structures that can be dismantled with a view to being re-used should not be considered as temporary.