Snow Loads

This load wizard facilitates the task of placing snow loads on members of the model in compliance with standards.

Dialog Box "New Load Wizard | Snow Load"

Main

The Main tab manages the geometry parameters of the roof.

Roof Type

Two basic roof shapes are available for selection in the list:

• Flat/Monopitch roof
• Duopitch 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 defining them.

Defining Roof Plane Nodes

Set Loaded Roof

The table provides an overview of the properties of the roof plane(s). For a duopitch roof, both roof pitches are set. If necessary, you can use the check boxes to exclude a roof side from the load assignment.

Generated on Members No.

This dialog section shows the members that get a proportional snow load. The entry in the 'Loaded' column is available as soon as the snow load is generated from the complete specified data after using the button.

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

Defining Load-Free Members

Parameters

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

Defining Snow Load Parameters

Definition (for German National Annex)

If you have adopted the location from the online map in the 'Model Parameters' tab of the 'Base Data' dialog box, the 'Map and parameters' definition type is preset. The snow load is determined automatically. Use the button to open the snow load map, also in this tab.

The 'User-defined' definition type allows you to manually define the snow load zone, the ground elevation, and the value of the characteristic snow load.

Parameters

If the 'Load zone' (for German National Annex) is not entered automatically, you can select it in the list. The entries are aligned with the standard you defined in the Standards I tab of the Base Data dialog box.

The 'Altitude' is usually 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 data. If you want to change the value, tick the 'Manual snow load definition' check box.

Coefficients

The 'Exposure coefficient' C_e indicates the decrease or increase of the snow load acting on the roof of the building. EN 1991-1-3, Table 5.1 provides recommendations for different topographies.

With the thermal coefficient C_t, you can consider reduced snow loads acting on roofs by higher thermal transmittance.

Load distribution

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

Options

Use the check boxes in this dialog section to control whether additional snow loads such as 'Snow overhang' on eaves or loads on a 'Snow guard' are taken into account (in preparation).

If you tick the 'Lock for new objects' check box, the snow load acts only on the currently available members of the roof plane(s) according to the definition set in the 'Main' tab. Any members you add to the roof plane later will not get any components 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 for which an out-of-plane offset is available.

With the 'Consider section distribution' check box, you can control whether the snow load resulting from a taper definition also acts on the inclined members (default setting). If you activate the check box, the snow load will not be applied to members within the load plane that have a non-uniform cross-section distribution (see the Section chapter).

Load Cases

The Load Cases tab controls the load cases where the snow loads are stored.

Defining Load Cases

In the list, enter the load case number(s) for generating the snow loads. Alternative load cases occur when additional snow loads or shape coefficients for snow loads on duopitch roofs apply (see EN 1991-1-3, Figure 5.3). You can create the corresponding load cases with the button.

Results

In the Results tab, you will find an overview of the parameters used for generating snow loads.

Generated Snow Loads

The table shows the 'Shape coefficient' μ and the 'Snow load' s. In the case of a duopitch roof, you can check the values for each load case and each roof side.