I have a Validation > Model > Concrete Cores > “Rigid section behaviour is not guaranteed due to uncoupled members” warning. Why do I get this and how do I resolve it?

Tekla Structural Designer
2021
Tekla Structural Designer
2020
Tekla Structural Designer
2019i
Tekla Structural Designer
2019
Tekla Structural Designer
Rigid Section
concrete core
validation
Environment
Australia
British Standard
Eurocode
India
USA
Not environment-specific

Question

I have a Validation > Model > Concrete Cores > “Rigid section behaviour is not guaranteed due to uncoupled members” warning. Why do I get this and how do I resolve it?

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Background

Cores in Tekla Structural Designer can create single entities out of mixed groups of Concrete Walls (designated as Meshed and Mid-pier), Concrete Columns and Concrete Beams, which for the main purpose of this feature are expected to act monolithically. This monolithic behaviour however,  is not enforced by the creation of a Core, and validation has been put in place to assist in highlighting cases of accidental disconnectivity.

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In certain situations, such as when Core results are required in the Core Principal Axis system, sections require rigid body behaviour.

 
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This behaviour is ensured for Cores in Tekla Structural Designer by having the Columns, Walls and Beams part of a Core correctly interconnected in the solver model.

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There is however, an exception with Concrete beams. Because these can be designated as Construction - Concrete beam (default) or Coupling beam, only the latter has been considered for the purpose of ensuring rigid body behaviour.

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If you set the Construction as a Coupling beam, you have made an engineering decision that you are satisfied the section is sufficiently stiff to provide rigid section behaviour - Tekla Structural Designer does not check for this.

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Cores can be generated manually, or by using an Assisted method.
  • In Manual mode, you can add either a Concrete beam or Coupling beam type to the Core, in addition to Concrete Walls and Concrete Columns.

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  • In Assisted mode, the software only looks for Concrete Beams designated as Coupling beams, in addition to Concrete Walls and Concrete Columns.

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Answer

The two most likely reasons for the issuing of this validation warning are:
  1. The Core contains one or more sets of members disconnected from each other in the analytical model, or connected by an object not in the Core,
  2. The Core contains one or more sets of members connected between themselves in the analytical model by a Concrete beam included in the Core but of construction type other than Coupling beam.
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You have a number of options for each case:
 
  1. If there are sets of disconnected members then,
    1. Create a different core for each disconnected set of members, or,
    2. Link the disconnected sets of members between themselves with a members which allows for rigid section behaviour, or
    3. Evaluate if rigid section behaviour is required and if not, ignore the warning,
  2. If the connecting Concrete beams in the Core are not of Coupling beam construction type,
    1. If you consider that the Concrete beam included within the Core, will provide sufficient rigid section behaviour, then you can change the Construction of each beam to a Coupling beam
       

       

      You have made an engineering decision that you are satisfied the section is sufficiently stiff to provide rigid section behaviour.

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      The validation warning will be removed.

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    2. If you consider that the beam does not provide sufficient rigid section behaviour, and connectivity is not essential, then you will need to edit the Core so that the Concrete beams are not included.

       

      To edit the Core, you can locate the Core in the Project Workspace Structure window, right click and choose Edit Core from the context menu. You can then use the Properties window to set the Mode to Modify, Selection Mode to Toggle and click on the beams in the active Scene view to remove them from the Core.

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      The Validation warning will be removed.

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    3. Ignore the Warning. This is your Engineering decision and should be based on your understanding of 1 and 2.

       

      You can hide all warnings of this type via Model Settings > Validation, by unchecking the option Rigid Sections

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