2021 SP3: New & Enhanced Loading Features - Minimum Lateral Load, Seismic Loading, Snow Loading and Imposed/ Live Load Reductions

Tekla Structural Designer
2021
Tekla Structural Designer

2021 SP3: New & Enhanced Loading Features - Minimum Lateral Load, Seismic Loading, Snow Loading and Imposed/ Live Load Reductions

Reflecting the worldwide use of Tekla Structural Designer, in this release we have focused on making the program more flexible by both enhancing the automated loading features and extending their applicability to more Head Codes. This makes Tekla Structural Designer more widely usable, especially for regions and countries for which the design codes may not be fully supported currently.

  • [TSD-9815] - Automated Minimum Lateral Loads

    Many design codes require consideration of a minimum lateral design load as a proportion of the gravity loads. A new feature automates the calculation and application of such loading - see below for more details.

  • [TSD-9613] - Use of the Seismic Wizard for other Head Codes

    The existing Seismic Wizard variants can now be used to apply seismic loading for any Head Code - see below for more details..

  • TSD-9707] - Use of the Snow Wizard for other Head Codes

    Automated snow loading via the Snow Wizard has been available for the Eurocode and USA Head Codes for some time. Some aspects of this are now made available to other Head Codes - see below for more details.

  • [TSD-9619] - User-defined Imposed Load Reductions - Eurocode Head Code

    The Imposed load reduction percentage can now be edited for the Eurocode Head Code - see below for more details.

Automated Minimum Lateral Loads

A new option “Minimum Lateral Loads” (MLL) has been added in Model Settings immediately below the Loading group as shown in the picture below and is available for all Head Codes.
  • In some Head Codes MLL will be a minimum wind load case, in others a robustness check - some examples of the application of MLL are:

    • The USA code (ASCE7-16 clause 1.4.2) recommends a value of 1% of total dead load as a minimum lateral design force.. For more on this see Minimum lateral loads (MLL) (ASCE7)

    • Eurocode - the Singapore National Annex to EN 1991-1-4 Wind Actions requires that buildings should be capable of resisting, as a minimum, a design ultimate horizontal load equal to 1.5% of the characteristic dead weight of the structure. For more on this see Minimum lateral loads (MLL) (Eurocode)

    • British Standard (BS 5950) recommends a value of 1% of factored dead load as a minimum lateral load replacing wind load For more on this see Minimum lateral loads (MLL) (British Standards)

  • Settings
    • Default settings - these depend on Head Code as follows:

      • For the USA, Singapore (Eurocode) and Malaysia (British Standards) MLL is switched on and set to Case A.

      • For other Head Codes it is switched off i.e. set to None.

  • The MLL load is a percentage of gravity loading, with the gravity load to be considered configured as follows:

    • Gravity Loads - either Dead or Dead & Imposed can be selected.

    • Using Combination - either Unfactored or Factored Loads can be selected.

  • There are potentially two sets of loading that can be applied - Case A and Case B - each of which creates four loadcases acting on the structure in the +ve and -ve Building Directions.

    • When Case A or Case A & B are enabled, you specify the percentage loading for both directions (Dir 1 & Dir 2) as shown in the picture below.
  • Application
    • Load Cases - when Case A or Cases A & B are enabled, the appropriate “Min Lateral Load” load cases are automatically created and listed in the Loading dialog as shown below. These can be manually included in combinations or via the Combination Generator in a similar manner to Notional/ Equivalent Horizontal Loads (NL/EHL).
    • Load Combinations - When the MLL Model Setting option is enabled, additional “+MLL” combinations are included for all Gravity combinations listed on the second page of the Combination Generator as shown in the picture below. You can then select which of these you wish to include.
      • As you proceed through the Combination Generator, a new MLL page is now displayed - after the Generator’s NL/EHL page - as shown in the picture below. On this page you specify 1) in the drop list at the top the combination to be used for the MLLs and 2) in the table of combinations the applied load direction(s) for each active MLL combination.

      • The combination used for the MLL is set via a check box in the combinations main list in a new column headed “Min Lat Load” next to the existing “Camber” column, as shown in the picture below. Only Gravity Class combinations will be available for selection in this column. You can make the selection of the MLL combination via the Combination Generator as described above, or manually via this check box.
  • Review - The MLLs are automatically calculated and applied during analysis in the same manner as NL/EHL. They can also be reviewed graphically in the same manner in the Results View via the new “MLL” button in the Notional/ Seismic Loads group of the ribbon, as shown below. The Min Lateral Load cases are listed together with the other load cases in the load case/ combination selection drop list as are the MLL combinations.
    • The MLL cases are also listed in the Loading window of the Project Workspace where the total MLL applied can be seen as shown below.

Use of the Seismic Wizard for other Head Codes

The Seismic Wizard can now be run for all Head Codes, where previously it was available only for certain Head Codes. The variant of the Seismic Wizard which is run is determined by the Seismic Loading code set in Model Settings > Design Codes. As shown in the picture below, all the currently available Seismic Loading code options are now listed for selection for all available Head Codes.

  • This new feature means that it is now possible to select a seismic code that does not match the Head Code, thus enabling seismic loading to be applied for Head Codes that have no Seismic Loading code and hence no Seismic Wizard variant, such as British Standards.

  • Though it is less likely to be required, as part of this enhancement it is also now possible to do this for Head Codes that do have a Seismic Wizard variant - such as the USA and Eurocode Head Codes. Previously the Seismic Loading options available were fixed to those matching the Head Code - for example ASCE7 and UBC for the USA Head Code.
  • In all cases the validity of setting a mismatched Head Code and Seismic Code is at the discretion of and the responsibility of the engineer. The warning shown below is always issued when this is the case.
  • When seismic loads are generated for a mismatched Head Code the following applies:

    • Generated seismic loads are based on the selected Seismic Loading Action Code.

    • Generated seismic load combinations are based on the Combinations Action Code (which is determined by the model Head Code).

      • Thus no seismic combinations will be created by the Combination Generator for Head Codes the Action Code of which does not consider seismic loading, such as British Standards. In such cases the engineer must manually create seismic combinations.

    • Seismic Drift checks are based on the selected Seismic Loading Action Code (NOT the Model Head Code).

    • Conventional static design of members (to the selected Resistance Codes) will be performed for the results of the seismic combinations.

    • However, for Head Codes that feature specific seismic member design checks for members of Seismic Force Resisting Systems - such as the USA Head Code and seismic checks to AISC 341 and the seismic provisions of ACI 318 - these checks will NOT be performed in the case of mismatched seismic loading and Head Code.

Use of the Snow Wizard for other Head Codes

The Snow Wizard loading option is now available for the Australian, British Standards, and Indian Head Codes. It is launched in the same manner as for the previously supported Head Codes via the Snow Load > Snow Wizard command of the Load ribbon. It is used in a broadly similar manner, though its functionality for the new Head Codes has some limitations in comparison to the existing variants for the USA and Eurocode Head Codes as described below. For the basics of using the Snow Wizard see the Help topic Snow loads and the snow wizard .
  • The functionality is the same for all the new Head Codes; as shown above, you can automatically generate the following snow load cases using the Snow Wizard;

    • Balanced snow load (a single case)

    • Unbalanced snow load - up to four cases.

    • Drift snow load - up to four cases.

  • The generated Snow load cases are listed in the Loading dialog and can be included in combinations in the usual manner - either using the Combination Generator or manually - and appropriate combination factors are applied.

  • Application of snow loads in the generated snow load cases is not automatic. However the snow wizard load functions of Uniform Snow, Valley Snow and Local Drift Snow can be used to quickly and easily apply these types of load to Roof panels. These work in a broadly similar manner to the previously supported Head Codes, the main difference being that the load values - such as maximum load values and drift length etc - are specified directly.

Imposed Load Reductions - User-defined reduction % values - Eurocode Head Code

For the United Kingdom (Eurocode) and Malaysia (Eurocode) Head Codes, the Imposed Load Reductions percentage values in Model Settings > Imposed Load Reduction can now be edited where previously they were fixed. This makes the program more flexible, allowing the user to adjust the reduction values should they need to.
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