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Work with check lines

Added August 6, 2019 by Admin admin

Software version: 
Tekla Structural Designer 2019

Work with check lines

Work with check lines

User defined Check Lines can be placed across 2D element meshes, They are similar to 2D results strips, (but with zero width and different properties).

From these check lines, deflection results are determined from the shell/plate/membrane nodal analysis results - these can then be checked against specified limits for slab design purposes.

Engineering judgement is required when positioning the check lines to ensure worst case deflections are obtained.

What are check lines?

Check lines - a unique feature in Tekla Structural Designer - provide a practical way to automate deflection checking and reduce the possibility of errors.

Each check line defines a line along which deflection checks are required. Multiple check lines can be created and each line can have several different deflection checks performed (against either a total, instantaneous, or differential deflection limit).

Whilst the check lines have to initially be positioned using engineering judgement, once they are in place they provide an instantaneous means to evaluate revised deflections following changes to the model parameters and re-analysis.

Assessing slab deflections without check lines would be quite an arduous task, since deflection limits are of the form (span / fixed value) and the spans can vary on an irregular slab, hence the permissible limit would also vary. Furthermore, you may wish to check total or differential deflections at or between different load events. Would the critical location be obvious?

Setting up the checks in advance

The deflection checks to be performed for the check lines are set up in the Slab Deflection Check Catalogue before the check lines are positioned.

Each check in the catalogue is specified as a Total, Differential or Instantaneous deflection limit that is checked for a specified event, (or in the case of a Differential check between the start of an event and the end of an event).

Application of check lines

The application of check lines is an iterative activity. They should be created at all locations where you deem deflection checks to be required.

Check lines can only be created in a 2D view. If the Create command is greyed out ensure you switch to a 2D view.

When you click Create, the Properties Window automatically includes those slab deflection checks from the Slab Deflection Check Catalogue where "Use in new Check Lines" was checked. Note that a maximum of six checks can be assigned to a single check line; if you require more than six checks, then multiple check lines can be applied at the same location.

You can add further checks from the catalogue or add new checks directly from the Properties Window.

You can also edit the "Use in New Check Lines" option in the catalogue prior to running the Create command to change the default checks automatically assigned to each new check line.

Displaying check line results

The Check Line deflection can be overlayed on the slab by using the Deflections command in the ribbon, it is perhaps easier to visualise if you switch the view to a 3D view of the slab using the 2D/3D toggle button in the bottom right of the window.

You can also right click on a check line and open the deflections check view. This displays a cut line through the slab, showing the deflected shape with the maximum and minimum deflection values. Beneath this it also draws the average slopes between maximum and minimum points and reports the average slope ratios.

The above deflection check view is controlled from the Loading Analysis ribbon which has droplists to enable you choose the Result Type (Total, Instantaneous, or Differential) and the Event(s).

The average slope ratios (for the appropriate result type/event) are checked against the deflection limits that have requested for the check line.

Doing the checks this way inherently deals with offset peak deflections (non-uniform load) and also cantilevers.

Related task Display check line results

Create the deflection checks to be applied to check lines

  1. On the Slab Deflection tab, click Deflection Checks The Slab Deflection Check Catalogue is displayed , containing any checks that have been defined.
  2. Click Add A new check is created in the table.
  3. Select the name in order to give it a more descriptive title.
  4. Choose the check Type : (Total, Instantaneous, or Differential).
    1. If the Type is Differential, select the Start Event from the droplist.
  5. Select the Event to check from the droplist.
  6. Enter the Deflection Limit to be checked.
  7. Select Use in new Check Lines if you want this check to be performed in each check line that is created.

Create a check line

Check lines can only be created while in the Slab Deflections View regime.

  1. Open a 2D view of the FE mesh where the check line is to be placed.
  2. On the Slab Deflection tab, click Create The Check Line properties are displayed in the Properties window.
  3. Adjust the properties to specify:
    1. The number of stations
    2. The upper and lower Flat Zone Reductions
    3. Up to 6 deflection checks to be performed (these can either be selected from the predefined Deflection Checks Catalogue, or a new check can be defined)
  4. Click a point where the strip is to start.
  5. Click a 2nd point where the strip is to end. (Neither start or end points have to match nodes in the mesh.) A check line is created between the points that you identified.
  6. Either continue to place further check lines, or if done, press Esc to exit.

Delete a check line

To be able to delete a check line you must first ensure that Slab Deflection Check Lines are switched on in Scene Content.

  1. Open a view displaying the check lines to be deleted.
  2. Click or press Delete
  3. Click on the check lines to be deleted.
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