Minimum lateral loads (MLL) (Eurocode)

Tekla Structural Designer
2021
Tekla Structural Designer

Minimum lateral loads (MLL) (Eurocode)

MLLs are sets of notional lateral loads that can be applied in order to cater for a minimum lateral loading for wind.

You are able to create up to two minimum lateral load sets, 'Case A' and 'Case B'. The loads in each set being specified as a percentage of gravity loading. These are then applied in the analysis as a horizontal force at each node in each level.

Settings to activate and define the MLLs are found in Home > Model Settings > Minimum Lateral Loads.

In addition to defining how the loads are to be calculated in Model Settings, you also are required to specify the gravity combination to be used for the calculation. This second part is done from the Loading dialog box - the required combination being identified by the Minimum Lateral Loads checkbox on the Parameters tab of the Combinations page.

The MLL loadcases are then made available in each of the building directions when creating load combinations.

Once you have specified the gravity combination to be used and performed the analysis, you can view the magnitude of the loads from the project workspace. You can also display their magnitude and direction graphically in a results view.

Note: There is a subtle/important difference between MLLs and EHFs - the EHF loading in every combination is dependent on the gravity loading in that combination. Min Lateral Load (MLL) - creates fixed loadcases which are then included in combinations. So the MLL case used in a combination can be based on gravity loads that don't exist in that combination.

Minimum lateral load requirements of the Singapore National Annex

The foreword to the “Singapore National Annex to EN 1991-1-4 Wind Actions” states:

  • “For continuation of an established design philosophy, all buildings should be capable of resisting, as a minimum, a design ultimate horizontal load applied at each floor or roof level simultaneously equal to 1.5% of the characteristic dead weight of the structure between mid-height of the storey below and either mid-height of the storey above or roof surface. The design ultimate wind load should not be taken as less than this value when considering load combinations.”

In Tekla Structural Designer this requirement can be catered for by setting up and designing for appropriate minimum lateral load combinations as described above.

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