Loads

Contents

• Constant load definition with resultant
• Master-slave relationship in load groups
• Enhanced combination of Temporary loads (Snow/Wind)
• Distinction of accidental snow load group
• Infrequent Load group combination (NS 1990 A2)

Constant load definition with resultant

For loads, a newly introduced tool allows the creation of constant line distribution and surface forces by specifying their resultant force value.

In FEM-Design, loads defined by resultant are distinguished from those defined by intensity, both in appearance and labelling.

Master-slave relationship in load groups

For load effects where X+, Y+, X-, or Y- directions can be assigned (e.g., wind load, deviation load), users can reduce the number of generated load combinations by combining effects with the same direction at Load groups.

A new “Direction” column has been introduced in the Relationships of load cases dialog and table, offering five direction options for assigning load effects. Only relations with the same direction can be combined across load groups (e.g., X+ relations in a 'Wind' load group combine only with X+ relations in a 'Deviation' load group). All directions must either be explicitly assigned or “Non-directional”. The “Non-directional” option has no impact on combination generation.

Macros for Wind loads (Shear wall load, Regular building, Generic building), Deviation loads, and Notional loads now include a control for automatically creating directional relations.

In the wind load generation macros, a new checkbox called Create directional relations in the resulting load group has been introduced in the dialogs. Enabling this option creates a new temporary load group containing the generated load cases. The relation of the load group is automatically set to “Custom” with the relation table populated using an alternative rule — each relation activates only one load case. Additionally, each relation is assigned the direction of its corresponding load case.

In the Deviation and Notional load macros, a new dropdown menu (Directional relations) has been added to the dialogs, offering three options:

• No generates load cases remain independent, so their combination generation is not affected.
• Yes, alternative generates load cases placed into a new permanent load group with all safety factors set to 1.0. The load group is assigned a “Custom” relation, and the relation table is generated using an alternative rule (only one load case is active per relation).
• Yes, multi-relational generates load cases placed into a new permanent load group with all safety factors set to 1.0. The load group is assigned a “Custom” relation, and the relation table is created such that each direction can also combine with one of its perpendicular directions.

Enhanced combination of Temporary loads (Snow/Wind)

The creation of unfavourable combinations that account for temporary loads (especially snow and wind effects) varies by the requirements of different Eurocode National Annexes. For example:

• EN 1990 6.11, Finnish NA (Accidental combination): If the highlighted temporary group is wind or snow, then ψ₁ is applied; otherwise, ψ₂ is used for the highlighted group.
• EN 1990 6.11, Norwegian NA (Accidental combination): If the highlighted temporary group is wind, then ψ₁ is applied; otherwise, ψ₂ is used for the highlighted group.
• EN 1990 6.11, Dutch and Belgian NA (Accidental combination): If the highlighted temporary group is wind and the combination is a fire combination (where the only accidental group in the combination contains a fire load case), then ψ₁ is applied; otherwise, ψ₂ is used for the highlighted group.
• EN 1990 6.10 and 6.11, German NA (Ultimate and Accidental combinations): If the altitude specified in the site load information is below 1000 m and the highlighted temporary group is general type, then only one snow or wind group can be included in the combination.

To ensure that these specific NA requirements can be easily and efficiently met using automatic load combination generation — without the need for manual combination modifications — FEM-Design 24 introduces the ability to categorise temporary load groups by type: General, Wind, or Snow. This categorisation drives the correct application of the appropriate ψ-factors required by various Eurocode NAs.

Distinction of accidental snow load group

FEM-Design 24 allows us to configure the “Accidental snow” load group to exclude combinations with temporary snow load groups during accidental load combination generation.

The following image demonstrates the difference in combination generation when accidental snow is distinguished or not distinguished.

To enable this distinction, the new Snow effect option must be activated to specify a load group as accidental snow, and the new Snow type option must be used to define the temporary snow loads.

Infrequent Load group combination (NS 1990 A2)

A new preset, called "NS 1990 A2 - Infrequent", has been added to the Custom combination methods of Load groups.

This preset follows the infrequent combination rule defined in NS EN 1990 Table NA A2.6 (Norwegian annex). The generated load group combinations are classified in frequent limit state.