Wind Loads

The load wizard simplifies the task of applying wind loads to members of the model in accordance with the standard.

Dialog Box "New Load Wizard | Wind Load"

Basic

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

Structure Definition

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

• Building
• Freestanding roofs

Type

Depending on the structure definition, the list provides the following building or roof shapes for selection:

• 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 'base corner nodes' of the building. Use the button for this purpose and click the four corner nodes of the footprint one after the other in the work window.

Then, as with 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 upper wall nodes, not the roof nodes.

Defining Roof Plane Nodes

Wind Direction Perpendicular To / Wind Direction In Direction

The table lists four flow directions. 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 required, you can exclude wall or roof sides from the load assignment using the check boxes.

Generated on Members No.

This section specifies the members that receive a partial wind load. The entries are available as soon as the wind load is generated from the complete specifications using the button.

To exclude specific members from load transfer, click a field in the 'Without Load' column. You can then use the button to select in the work window the members that are load-free, such as bracing or purlins. You can also define a template member that runs parallel to the unloaded members. This way, you do not need to select the members individually.

Defining Members 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 select the 'Ignore New Load-Bearing Objects' check box, the wind load acts only on the objects specified in the section Generated on Members No.. Members you add later in the load plane do not receive any portions 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. The loads are generated only for the elements of these partial areas. The remaining areas do not receive any wind loads.

Defining Partial Areas of Wind Load

Define the partial areas row by row 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 for generation into account.

Defining Wind Load Parameters

Definition

If you adopted the location from the online map in the basic 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 specify the wind zone, terrain category, sea level elevation, 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 under the model basic data.

The 'Terrain Category' and the 'Elevation above sea level' are usually preset from the model parameters, but they 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 geographical information. If you want to change the value, select the 'Manual Wind Velocity Definition' check box.

Coefficients

The 'Direction factor' c_dir and the 'season factor' c_season are used to determine 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 variations.

Load Distribution

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

Options

If you select the 'Lock for New Objects' check box, the wind load acts only on the currently existing members of the planes according to the definition in the 'Basic' tab. Members that you add later in a wall or roof plane do not receive any portions 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 that are 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 that result from a haunched definition (default). If you activate the check box, the wind load is not applied to members in the load plane that have an uneven cross-section progression (see chapter Cross-Section ).

If you select the 'Consider Internal Pressure' check box, you can define the internal pressure coefficients c_pi for each wind direction in an additional category. This allows effects caused by openings in walls to be taken into account. The technical article Determination of Internal Pressure Coefficients (cpi) for Single-Storey Buildings According to EN 1991-1-4 provides detailed information on this topic.

For load generation according to AISC 7, you can also 'Consider 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 defines in which load cases the wind loads are stored.

Defining Load Cases

Define 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 taken into account for a mono-pitch roof. For this purpose, the pressure loads are generated in the 'Case w+', and the suction loads in the 'Case w-'. You can create the corresponding load cases using the button.

Results

In the Results tab, you find an overview of the parameters for generating 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 zone. This allows you to check the wind pressures acting on the external surfaces of 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.