ESICS: Wind Pressure - General
In this section, the user can decide whether they would like manual, semi-automatic or fully automatic wind calculations. Figure 1 demonstrates the default mode of the "Wind Pressure - General" section of the bracket checker calculator for a site located in the UK. As seen in Figure 1, Wind calculations are in fully automatic mode for both "Wind Peak Velocity Pressure" and "Terrain Category". However, in some instances, the design may require considerations not present in this calculator, such as dynamic effects; therefore manual entry of the Wind Peak Velocity Pressure is recommended.
Figure 1. Wind Pressure - General Section in ESCIS Calculators
This is carefully selected by the calculator based on the location given in the project details and the methods defined in the standard Eurocode and the specific National Annex for detecting terrain categories. Two terrain categories of “Town” and “Country” are defined in the UK National Annex whereas, in the UK National Annex, the terrain categories are divided from 0 - IV. Keep in mind, if this was incorrectly detected by ESICS, you can manually override this selection by setting “Automatic or Manual Terrain Category” to “Manual” and selecting the proper terrain Category.
Base Wind Velocity Map
According to BS EN1991-1-4, the fundamental value of basic wind velocity is defined as the 10-minute mean wind velocity with a 0.02 annual risk of being exceeded, irrespective of direction and season, at 10m above ground level in terrain Category II. The values of basic wind velocity are given for each Member State in the corresponding National Annex. For example, The UK NA gives values in a map that has been adjusted to sea level, defining these as ‘map’ values, and introduces an altitude factor to adjust these values to the required base. ESICS calculators used the map shown in Figure 2 and the location of the project to automatically detect the Base wind velocity. As seen in Figure 1, the "Altitude of the Site" is also automatically measured to further calculate the altitude factor.
Figure 2. Value of Fundamental Basic Wind Velocity, Before the Altitude Correction, is Applied. Figure NA.1, BS EN1991-1-4
Keep in mind not to confuse base wind velocity from the map with basic wind velocity which will be explained in section 4 of this report. At the moment there is no manual override of the basic wind velocity from the map, therefore if the automatic value is not satisfactory to the user they have to select the manual entry of the Wind Peak Velocity Pressure and manually perform the entire calculation for this value.
Height from Ground/ Season Factor
Height from the ground and the season factor are the two variables that cannot be automatically detected by ESICS and should be inputted by the user. Height from the ground is referring to the average height of the system being designed from ground level. For example, if the user is designing a freestander that is on the roof of a 25 m building and the equipment is placed 1 meter above the building's roof, the height above the ground will be 26 m.
The main use of the seasonal factor is in assessing wind loads on temporary structures and on structures during construction. Therefore if a system is being installed for more than 12 months then the recommended value of the season factor is 1.0. If the system installed will be used in a temporary construction this factor may be reduced. Please refer to specific National Annexes for country-specific values. For example, table NA 2.7 demonstrates the designated season factor in the BS EN1991-1-4.