Snow Loads

This load generator facilitates the task of applying snow loads to the members of the model in compliance with standards.

Dialog Box "New Load Wizard | Snow Load"

Base

The Base tab manages the geometry parameters of the roof.

Roof Type

There are two basic roof forms available in the list:

• Flat/mono-pitch roof
• Gable roof

Define the boundary of the roof plane by clicking the four or six corner nodes of the plane(s) one after the other in the work window. Use the button for this.

Defining Roof Plane Nodes

Define Loaded Roof

The table provides an overview of the properties of the roof plane(s). For a gable roof, both roof halves are specified. If necessary, you can exclude one roof side from the load assignment using the check boxes.

Generated on Members No.

This section specifies the members that receive a proportion of the snow load. The entry in the 'Loaded' column becomes available as soon as the snow load is generated from the complete input using the button.

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

Defining Load-Free Members

Options

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

If you check the 'Ignore New Load-Bearing Objects' box, the snow load acts only on the objects specified in the Generated on Members No. section. Members that you later add in the load plane do not receive any portion of the snow load.

Partial Areas

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

Defining Partial Areas of Snow Load

Define the partial areas row by row by entering their 'Corner Nodes'. You can also define the partial areas graphically using the two buttons at the end of the table.

	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 generation.

Defining Snow Load Parameters

Definition

If you adopted the location from the online map in the basic data of the Model Parameters tab, the definition type 'Map and Parameters' is preset. The snow load is determined automatically. You can also open the snow load map in this tab using the button.

With the definition type 'User-Defined', you can manually specify the snow load zone, elevation, and the value of the characteristic snow load.

Parameters

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

The 'Elevation' is generally preset from the model parameters, but can also be defined manually. It affects the characteristic value of the snow load.

Snow Load

The characteristic value of the snow load s_k on the ground at the structure is preset from the geographical information. If you want to change the value, check the 'Manual Snow Load Definition' box.

Coefficients

The 'Exposure Coefficient' C_e specifies the reduction or increase of the snow load on the roof of the structure. In EN 1991-1-3, Table 5.1 you will find recommendations for different terrain conditions.

With the temperature coefficient C_t, you can take reduced snow loads on roofs with higher heat transmission into account.

Load Distribution

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

Options

Using the check boxes in this section, you can control whether additional snow loads such as 'Snow Overhang' at the eaves or loads on a 'Snow Guard' are to be taken into account (Eurocode only).

If you check the 'Lock for New Objects' box, the snow load acts only on the members of the roof plane(s) currently present according to the definition in the 'Base' tab. Members that you later add to a roof plane do not receive any portion of the snow load.

The 'Consider Member Eccentricity' option controls whether the snow load acts on the members in the plane without considering eccentricities (default setting). 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 snow load also acts on the inclined members resulting from a haunch definition (default setting). If you activate the check box, the snow load is not applied to members in the load plane that have a nonuniform cross-section variation (see chapter Cross-Section ).

Load Cases

The Load Cases tab defines in which load cases the snow loads are stored.

Defining Load Cases

Enter the load case number(s) for generating the snow loads in the list. The alternative load cases arise when additional snow loads or shape coefficients for snow loads on gable roofs apply (see EN 1991-1-3, Figure 5.3). You can create the corresponding load cases using the button.

Results

The Results tab provides an overview of the parameters for generating the snow loads.

Generated Snow Loads

The table specifies the 'Shape Coefficient' μ and the 'Snow Load' s. For a gable roof, you can check the values for each load case and each roof side.

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 Load.