Eurocode 1 - probability factor cprob

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 c_prob to calculate the basic wind velocity v_b with a return period equivalent to the design working life of your building.

v_b0 is the fundamental value of the basic wind velocity given by the maps in the national annexes.
c_dir is the directional 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.

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 c_prob : K=0,2 and n=0,5.

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 c_prob :

• 0.02 < p : K=0.15 and n=0.5
• p < 0.02 : K=0.20 and n=0.5

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 c_prob :

• 0.02 < p : K=0.20 and n=0.5
• p < 0.02 : K=0.138 and n=1.0