Beam end releases and partial fixity

Tekla Structural Designer
2021
Tekla Structural Designer

Beam end releases and partial fixity

The following beam end release options are provided:

  • Pin - Pinned to the support or supporting member. This means pinned about the major and minor axes of the section but fixed torsionally.
  • Fully fixed - with the following major (My), and minor (Mz) stiffness sub-options to allow definition of partial fixity in each direction if required:
    • Fixed - Encastré, all degrees of freedom fixed.
    • Spring linear - allows you to specify a linear spring stiffness value.
    • Partially fixed - allows you to specify partial fixity as a percentage of the member flexural stiffness (%4EI/L)
  • Moment (pin Mz) - Major axis moment connection, and pinned about the minor axis.
  • Moment (pin My) - Minor axis moment connection, and pinned about the major axis.
  • Fully fixed (free end) - Denotes a cantilever end. It is achieved by selecting Free end.
    • In a single span beam this box can only be checked if the opposite end is fully fixed.
  • Continuous - This setting is automatically applied when a continuous beam is created and effectively creates a non-editable fully fixed connection between the spans of the continuous member. The connection can only be edited by splitting the beam.

In addition to the above release options you are also able to apply a torsional release at either end by checking the appropriate box. Similarly an axial release can be applied to beams of all materials apart from concrete.

While beam end releases can be set directly in the Properties window/Properties dialog they can also be set or toggled graphically in a Review View as follows:
  • Use the Show/Alter State Fixed/Pinned attribute to review or apply pinned/fixed ends
  • Use the Show/Alter State Rotational stiffness attribute to review or apply partial fixity/rotational springs

Partial fixity

The partial fixity option is especially useful for example when modeling precast concrete structures in which it is common to consider some amount of end fixity, but not full end fixity (which is commonly assumed for in-situ concrete buildings).

  • To apply the Partially fixed setting, first set the end Fixity to Fully fixed to enable the fixity options of Spring linear and Partially fixed.

    • For Spring linear a value of stiffness in moment/rad is directly entered.

    • For Partially fixed a % value is entered. Note that this is the % of the member flexural stiffness (4EI/L) and not of full fixity (which is infinitely stiff). The resulting stiffness is automatically calculated and applied in the analysis model.

End fixity settings can also be applied and verified efficiently via Review View > Show/Alter State, using the Rotational Stiffness Attribute.

  • Use Set mode to rapidly apply or edit the % Partial fixity and Rotational stiffness values.

  • Use Review mode, to display the values in an automatic color-coded range.

Related video

Automatic modelling of partial fixity

Moment (pin My)

This (unusual) release type is not available in the Properties window and can only be specified as follows:
  1. Right-click the beam to display the context menu.
  2. Choose Edit
  3. From the Beam Property Dialog open the Releases page.
  4. Check the Mz and uncheck the My degree of freedom at the desired end as required.
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