Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

In the field of structural engineering, ensuring the safety and integrity of buildings and structures is of paramount importance. One crucial aspect of this process involves calculating the effects of wind forces on structures, as the wind can exert significant pressure and induce structural vibrations. Eurocode 1 (EN 1991-1-4) serves as a comprehensive standard for wind actions on structures within the European Union. This code provides engineers with guidelines and procedures for accurately assessing wind loads and their impact on various types of structures.

The theoretical background underlying the wind calculation methods prescribed in Eurocode 1 (EN 1991-1-4) is fundamental to understanding the rationale behind its provisions. 

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

 

Z0 - Roughness length, from Table 4.1 
Zmin - the minimum height, from Table 4.1 
vm (z) - Wind velocity at height

                                Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

lv (z) - Wind turbulence

                               Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

ce(z) - Exposure factor

                                Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

qb - Basic velocity pressure

                                 Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

qp(z) - Peak velocity pressure at a height

                                  Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

NOTE: For various national annexes the obtaining of qp(z) may vary.

 

CsCd - Structural factor equal to multiplication of the size factor CS and the dynamic factor Cd.

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

aerodynamic admittance functions Rh and Rb

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Cf - The force coefficient

Cf = 1.8                                                                                        7.4.3 (7.7)

The geometry and position of the force are also described in Figure 7.21.


NOTE: The user will get a warning at the automatic generation of the loads if the height conditions above are not fulfilled.

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

 

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Where:

A is the sum of the projected area of the members and gusset plates of the face projected normally to the face.


Ac is the area enclosed by the boundaries of the face projected normal to the face = d ∙ l (d is the width of the lattice and l is the length of the lattice). 

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Where:

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

we - Wind internal pressure

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Where:
ze is the reference height for the external pressure given in Section 7
cpe is the external pressure coefficient. The coefficient, the position and the geometry of the external pressure are defined at Section 7, in:

 

wi – Wind external pressure

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

Where:

zi is the reference height for the internal pressure given in Section 7

cpi the internal pressure coefficient is defined in section 7 in 7.2.9 Internal pressure.

 

- Wind bet pressure:

1. For an element of the type "Building", "Protruding roof" or "Vertical roof slope (shed)":

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Knowing that for a specific structural part: ‘5.2 (3) The net pressure on a wall, roof or element is the difference between the pressures on the opposite surfaces taking due account of their signs’ and

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 


For the standard EC1 and the EC1 French annex, the formula includes also the correlation coefficient Kdc for the windward or sheltered windward walls, resulting:

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

For parapet walls, canopies, or awnings

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

 

Where cp,net is the net pressure coefficient. The coefficient, the position, and the geometry of the net pressure are given in Section 7.

NOTE: For canopies the automatically generated loads are based on both the force coefficient cf and the net pressure coefficient cp,net. There are no mixed types of loads in the same load case.

 

Fw - The resultant wind force used for outdoor panels (signboards), canopies or individual elements of lattices:

Eurocode 1 (EN 1991-1-4) Wind Calculation Theoretical Background

Where:
cf is the force coefficient for the structure or structural element, given in Section 7 or Section 8 (detailed above).
Aref is the reference area of the structure or structural element, given in Section 7 or Section 8.

 

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