I have a Validation > Model > General > “Raised support provides lateral restraint” warning. Why do I get this and how do I resolve it?

Environment

Not environment-specific

Question

I have a Validation > Model > General > “Raised support provides lateral restraint” warning. Why do I get this and how do I resolve it?

Note. This is a new validation warning introduced in Tekla Structrual Designer 2018. Prior versions did not flag this issue to your attention.

Answer

A raised support is a support that occurs on a higher (raised) level than the lowest support in the model.

A couple of situations where this warning can arise are listed below:

Where we have multiple foundation levels in the model.
Where we are trying to model support from an adjacent building - without physically modelling the adjacent building.

If we hover over one of the problem supports a tooltip is displayed “Review supports to ensure that lateral restraint is provided as intended - set as “free” if not”.

We can double click the “Raised support provides lateral restraint” warning or an individual support listed under the branch to highlight the supports or support in the model. Alternatively, you can right click and choose Highlight Items from the context menu. The support or supports are highlighted in the active scene view and their properties are displayed in the Properties Window to allow review or editing.

Note. In the screenshot above, the supports cannot be seen clearly due to the member geometry of the beams and columns obscuring the supports. To display the supports we could access Scene Content > Members and ensure that Geometry is unchecked. This ensures that the member wires are displayed and not the physical member.

The question then is… “Are these highlighted supports intended to be modelled at these locations and if so do you want them to provide lateral restraint?”

Obviously if they are not intended to be modelled and have been created in the model by mistake then they should be deleted using the Delete command.

The supports located to the right of the model, cover situation 1) where multiple foundation levels exist in the model. The side view below clearly shows the step change in the foundation levels.

The supports to the left of the model on the upper levels, cover situation 2) where supports are provided to model an adjacent building.

Each support has 6 degrees of freedom, translational F_x, F_y and F_z and rotational M_x, M_y and M_z. A typical pinned support is shown below.

You can view the Solver view regime to see the supports and the degrees of freedom.

Each support fixity is colour coded. Blue is X, Green is Y and Red is Z. A single arrow denotes translational fixity. A double arrow denotes rotational fixity.

So what support fixity do you require?

The warning “Review supports to ensure that lateral restraint is provided as intended - set as “free” if not” appears if the F_x (blue single arrow) and/or F_y (green single arrow) translational fixity or the rotational M_z (red double arrow) is set to Fixed. This is because the identified supports are constraining the model from moving laterally (horizontally). If you do not want the support to constrain the model horizontally, then set the F_x and/or F_y translational support and/or M_z rotational fixity to Free. For the case of situation 1) multiple foundation levels - providing a translational restraint could introduce a large proppoing force that is not wanted.

Note that the warning will only be removed if F_x and F_y and M_z are set to Free. You may have a situation where you need to provide a lateral support in one direction only. In this situation the warning will still display.

Clearly the engineer is responsible for defining the appropriate support fixity, since all six degrees of freedom need to be considered. The Results view can be used to verify the results following an analysis or design.

We would also recommend that you review the related article in the right hand panel “I have a Validation > Model > Supports > “Support clashing with member length” warning. Why do I get this and how do I resolve it?”

Example. Deflection results assuming upper supports are “Fixed” or “Free”

Upper level supports set as Fixed.

When all highlighted upper level lateral supports are fixed translationally, the deflection in the direction of the applied wind load is zero and a horizontal support reaction (not shown) exists.

Upper level supports set as Free

When all highlighted upper level lateral supports are set as translationally Free, then deflection in the direction of the applied wind load exists since no resistance to lateral movement is provided by the support.