Managing diaphragm action in roof panels and slabs

Tekla Structural Designer
2021
Tekla Structural Designer

Managing diaphragm action in roof panels and slabs

Tekla Structural Designer forms diaphragms in every slab item of a parent slab when Diaphragm option is set to Rigid or Semi-rigid.

When a rigid diaphragm is specified, Tekla Structural Designer automatically applies nodal constraints to the associated slab nodes.

In turn, when a semi-rigid diaphragm is specified, Tekla Structural Designer creates a mesh of semi-rigid 2D elements within the slab.

Activate rigid diaphragm option within a slab

By default, Tekla Structural Designer automatically creates rigid diaphragm within slabs. If necessary, you can review and modify the setting for specific slabs as follows:

  1. Go to the Project Workspace.
  2. In the Structure tree, expand the Slabs branch.
  3. Select the slab that contains the diaphragm.
  4. In the Properties window, set Diaphragm option as required.
    Note: You can set the Diaphragm option as required in both slab item properties and parent slab properties. Either way, all slab items within the parent slab adopt the new setting.

Activate semi-rigid diaphragm option within a slab

You can form semi-rigid diaphragms in both one-way and two-way spanning slabs. In addition, you can review and modify the diaphragm properties by selecting the slab within which they are located.

  1. Go to the Project Workspace.
  2. On the Structure tree, expand the Slabs branch.
  3. Select the desired slab.
  4. In the Properties window, set Diaphragm option to Semi-rigid.
  5. If necessary, to adjust the flexibility of the diaphragm, type a value in the Divide stiffness by option.
    Tip: You can set the Diaphragm option as required in both slab item properties and parent slab properties. Either way, all slab items within the parent slab adopt the new setting.

Activate semi-rigid diaphragm option within a roof panel

You can form semi-rigid diaphragms in roof panels as follows:

  1. Go to the Project Workspace.
  2. On the Structure tree, expand the Roofs branch.
  3. Select the desired roof panel.
  4. In the Properties window, select Include in diaphragm.
    Note: You cannot form a rigid diaphragm within a roof panel.

Adjust semi-rigid diaphragm flexibility

When the Diaphragm option is Semi-Rigid a Divide stiffness by value can be set in the slab item properties. The same value is applied to all slab items in the same slab.

The stiffness determined from the material properties and slab thickness is divided by this value in order to adjust semi-rigid diaphragm flexibility.

Adjust global semi-rigid mesh properties

When a semi-rigid mesh is created the 2D solver element shape (triangular or quad), the degree of mesh uniformity, and mesh type adopted are obtained from the Structure Properties. These parameters can be overridden for individual sub-models by setting different values in the respective Sub Model Properties.

  1. Go to the Project Workspace.
  2. In the Structure tree, click Structure.
  3. Go to the Properties window.
  4. Accept or adjust the Semi-Rigid Mesh Size.
  5. Accept or adjust the Semi-Rigid Uniformity Factor.
  6. Accept or adjust the Semi-Rigid Mesh Type:
    • QuadDominant: mainly consists of quadrilateral 2D elements, but may use occasional triangular elements to create a better mesh.

    • QuadOnly: only consists of quadrilateral 2D elements.

    • Triangular: only consists of triangular 2D elements.

    Note: Beam elements are not split by semi-rigid 2D element nodes.

Apply different semi-rigid mesh properties at different levels

If you need to apply different semi-rigid mesh parameters at a specific level, you can do so by creating sub models.

  1. Create a sub model.
  2. In the Structure tree, expand the Sub Models branch.
  3. Select the sub model that you created.
  4. In the Properties window, select the Override model's option.
  5. Adjust the semi-rigid mesh size, uniformity factor and type according to your needs.

Identify the nodes constrained by rigid diaphragms

In order to see which nodes are constrained by diaphragms, see the following instructions.

In the Status bar at the bottom of the window, click Solver View.

A solver view opens. The rigid and semi-rigid diaphragms are represented as different colored shaded planes.

Nodes that are constrained by a rigid diaphragm:
  • Must lie within, or be on the edge of, the shaded rigid diaphragm plane.
  • Must be solid rather than hollow, or excluded.

Therefore, the following nodes are not constrained by a rigid diaphragm:

  • Solid nodes that lie outside the shaded rigid diaphragm plane.
  • Hollow, or excluded, nodes.

Exclude individual nodes from a rigid diaphragm

If necessary, you can exclude specific nodes from a rigid diaphragm. In order to do so, see the following instructions.

  1. In the status bar at the bottom of the window, click Review View.
    A review view opens.
  2. On the Review tab, click Diaphragm On/Off.

    The nodes are displayed as follows:

    • Included nodes are only constrained if they lie within or on the edge of a rigid diaphragm. If they lie outside the rigid diaphragm, they are not constrained by it.

    • Excluded nodes are always unconstrained.

  3. Click a node to switch whether it is included in the diaphragm or not.

Exclude slab items from a diaphragm

By default, Tekla Structural Designer forms a rigid diaphragm in all the individual slab items within a slab. However, you can decide to exclude specific slab items. In order to do so, see the following instructions.

  1. In the structure view, select the slab item that you want to exclude.
  2. In the Properties window, clear the Include in diaphragm option.
    Tip: You can also exclude individual slab items graphically in the Review View. On the Review tab, click Diaphragm On/Off and then click the slab item to include/exclude.
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