Wind Loads

The Load Wizard simplifies the task of applying wind loads to members and surfaces of the model in accordance with the standard.

Dialog Box "New Load Wizard | Wind Load"

Basis

The Basis tab manages the geometry parameters of the roof and, if applicable, the building.

Structure Definition

Specify whether the wind loads are to be generated on the roof and the walls of a building or only on the roof. The following options are available in the list:

• Building
• Free-standing roofs

Type

Depending on the structure definition, the following building or roof shapes are available in the list:

• Vertical walls with flat/mono-pitch roof
• Vertical walls with gable roof
• Flat/mono-pitch roof
• Gable roof

If you generate the wind load on walls with roof, first define the 'basic corner nodes' of the building. To do this, use the button and click the four corner nodes of the base area one after the other in the work window.

Then, as for wind load on roofs only, define the boundary of the roof plane by clicking the four or six corner nodes of the plane(s) again using the button. In the case of roof overhangs, select the top wall nodes, not the roof nodes.

Defining Roof Plane Nodes

Wind Flow Perpendicular To / Wind Flow In Direction

Four wind directions are listed in the table. The wind directions refer to the roof sides according to the graphic scheme. You can use the check boxes to control which directions are relevant for load generation.

Define Loaded Wall / Loaded Roof

The table provides an overview of the properties of the wall or roof plane(s). If necessary, you can use the check boxes to exclude wall or roof sides from load assignment.

Generated on Members/Surfaces/Lines No.

This section specifies the members, surfaces, and lines that receive a proportional wind load. The entries are available once the wind load has been generated from the complete data using the button.

To exclude certain members, surfaces, or lines from load transfer, click a cell in the 'Without Load' column. Then use the button to select the objects in the work window that are load-free, such as bracings or purlins. You can also specify a prototype member or prototype line that runs parallel to the unloaded members or lines. This way, you do not need to select the objects individually.

Defining Members and Surfaces Without Loads

Options

The 'Partial Areas' check box allows you to generate loads for specific zones of the building envelope. The wind load is applied only to the elements of the areas you define in the Partial Areas tab.

If you check the 'Ignore New Load-bearing Objects' check box, the wind load acts only on the objects specified in the section Generated on Members/Surfaces/Lines No.. Members, surfaces, or lines that you add later in the load surface do not receive any share of the wind load.

Partial Areas

In the Partial Areas tab, you can define zones of the roof and wall surfaces on which the wind load acts. Loads are generated only for the elements of these partial areas. The remaining areas receive no wind loads.

Defining Partial Areas of Wind Load

Define the partial areas line by line by entering their 'corner nodes'. With the two buttons at the end of the table, you can also define the partial areas graphically.

	Click the corner nodes of an area one after the other (see image Define Nodes).
	Click the cells one after the other (see image Select Cells).

Parameters

In the Parameters tab, you can define the load parameters and take special boundary conditions into account for the generation.

Defining Wind Load Parameters

Definition

If you have imported the location from the online map in the basis data in the Model Parameters tab, the definition type 'Map and Parameters' is preset. The wind load is determined automatically. You can also call up the wind load map in this tab using the button.

With the definition type 'User-Defined', you can manually define the wind zone, terrain category, elevation above sea level, and the value of the basic wind velocity.

Parameters

If the 'Load Zone' is not entered automatically, you can select it in the list. The entries are matched to the standard you defined in the Standards I tab in the model basis data.

The 'Terrain category' and 'Elevation above sea level' are usually preset from the model parameters, but can also be defined manually. They affect the basic value of the basic wind velocity. The 'Structure height' is taken from the model geometry in Load Wizards for walls. For wind loads on roofs, the value must be defined manually.

Wind Velocity

The basic value of the basic wind velocity v_b,0 is preset from the geographic data. If you want to change the value, check the 'Manual Wind Velocity Definition' box.

Coefficients

The 'Direction factor' c_dir and the 'season factor' c_season are included in the determination of the basic wind velocity (see EN 1991-1-4, 4.2).

Velocity Pressure

The 'basic velocity pressure' q_b according to EN 1991-1-4, (4.10) is required to determine the peak velocity pressure, which includes the mean and short-term velocity fluctuations.

Load Distribution

Currently, only trapezoidal loads are generated on members, resulting from the load portions.

Options

If you check the 'Lock for New Objects' box, the wind load acts only on the currently existing members, surfaces, or lines of the planes according to the definition in the 'Basis' tab. Objects that you add later in a wall or roof plane do not receive any share of the wind load.

The 'Consider Member Eccentricity' option controls whether the wind load acts on the members in the plane without considering eccentricities (default). If you activate the check box, the load is not applied to members with an offset from the plane.

With the 'Consider Cross-Section Distribution' check box, you can control whether the wind load also acts on the inclined members resulting from a haunch definition (default). If you activate the check box, the wind load is not applied to members in the load plane that have a non-uniform cross-section variation (see chapter Cross-section ).

If you check the 'Consider Internal Pressure' box, you can define the internal pressure coefficients c_pi for each wind direction in an additional category. This makes it possible to capture effects caused by openings in walls. In the technical article Determination of Internal Pressure Coefficients (cpi) for Single-Storey Buildings According to EN 1991-1-4 you will find detailed information on this topic.

For load generation according to AISC 7, you can also consider the 'torsional moment', which generates the wind load about the building axis. This additional moment always acts centrally about the building axis. The wizard generates different load cases for positive or negative torsion.

Load Cases

The Load Cases tab controls in which load cases the wind loads are stored.

Defining Load Cases

Specify for the individual wind directions in which load cases the wind loads are to be stored. As described, for example, in EN 1991-1-4, Table 7.3a, different pressure coefficients must be considered for a mono-pitch roof. For this purpose, the pressure loads are generated in 'Case w+', and the suction loads in 'Case w-'. You can create the corresponding load cases using the button.

Results

In the Results tab, you will find an overview of the parameters used to generate the wind loads.

Generated Wind Loads

The table lists the 'external pressure coefficient' c_pe and the 'external wind pressure' w_e for each load case and each zone. This allows you to check the wind pressures acting on the external surfaces for each wall and roof plane.

Tolerances

In the Tolerances tab, you can influence the criteria according to which members and nodes are evaluated as belonging to a plane or line. The parameters are described in chapter Member Loads from Surface Loads .