Sub models

Any structure can be split into a continuous series of sub-models working from the top of the building down to and including the foundations. Sub-models are used in:

Grillage chasedown (no slabs)
FE chasedown (with FE slabs)
Slab deflection analysis

In addition, they may also be used with different support conditions in FE load decomposition (with FE slabs).

If they don't already exist, sub models are automatically created for every level specified as a Floor in the Construction Levels dialog box at the point when a chasedown analysis is initiated.

Tekla Structural Designer performs chasedown analyses one sub model at a time. The topmost sub model is analyzed first, and then its support reactions are applied as loads for the analysis of the sub model below. The sequence continues until all sub models have been analyzed down to the foundation level.

Slab mesh parameters can be specified individually for each sub model if required.

You can also define sub models manually in the Sub Models dialog box and you can modify the default support conditions applied to individual sub-models, if necessary.

Definitions of sub model characteristics

Sub model: a part of the 3D model between two horizontal sub model divide planes.

Each sub model contains all members entirely between the two horizontal planes. For the columns, wall and braces split by a divide plane, the stacks and brace length above the top plane are included in the sub model, as are the stacks and brace length below the lower plane.
Sub model divide planes: horizontal planes that you can add, delete or move in the 3D structure. Sub model divide planes are notional and infinite. Tekla Structural Designer only allows the planes to cut through the structure where they only split the following members:
- Column stacks
- Wall stacks
- Steel braces
Sub model supports: the artificial supports that Tekla Structural Designer defines for the column and wall stack ends and braces that pass through the divide planes
Structure supports: the supports that the user has defined in the 3D structure
Column and wall stacks: the span length of a column or wall.
Volume of the sub model: the 3D space that exists between any two adjacent sub model divide planes.

Basic rules of sub models

When all sub models are considered together, they form the complete structure. Only column stacks, wall stacks, and braces that are split by sub model divide planes can be in several sub models. This means that:

Each member in the 3D model is in at least one sub model.
A sub model cannot contain a member that is already in another sub model, unless that member is a column, wall, or brace divided by a sub model divide plane.
A sub model must contain at least one beam member, one truss member, or one slab item.

Create sub models

Sub models allow you to apply different slab mesh parameters within your structure. To create sub models, see the following instructions.

In the Structure tree, double-click Sub Models.

The Sub Models dialog box opens.

According to your needs, do one of the following:

To	Do this
Automatically create sub models	Click Generate.
Manually create sub models	According to your needs, click Insert Above, or Insert Below.

If necessary, modify the height above the base of each level in the Level field.
Click OK.

Open a 3D view of a sub model

To display a sub model in its own 3D view, see the following instructions.

In the Project Workspace, open the Structure tree.
Expand the Sub Models branch.
Double-click the sub model.

Tekla Structural Designer opens a 3D view of the selected sub model.

Tip: To open a solver view of the sub model, right-click the sub model, and select Open solver view.

Delete sub models

If necessary, you can delete existing sub models in the Sub Models dialog box. For detailed information on deleting sub models, see the following instructions.

In the Structure tree, double-click Sub Models.

The Sub Models dialog box opens.
Select the sub model that you want to delete.
Click Delete.

Tekla Structural Designer deletes the sub model, and the floors are transferred to the sub model immediately above the deleted one.

Sub Model Properties

Select a sub model and then use the Properties window to view its properties.


Property	Description
Override model's	Select this check box in order to override the Structure meshing properties in the current sub model.
Shell Mesh Size	Defines the shell mesh size for two way spanning slabs in the sub model.
Shell Uniformity Factor	Defines the shell mesh uniformity factor for two way spanning slabs in the sub model.
Slab Mesh Type	Defines the shell mesh type used in the sub model. These options are: Quad only Tri only Quad dominant
Semi-Rigid Mesh Size	Defines the semi-rigid mesh size when slabs are modeled as semi-rigid diaphragms in the sub model.
Semi-Rigid Uniformity Factor	Defines the semi-rigid uniformity factor when slabs are modeled as semi-rigid diaphragms in the sub model.
Semi-Rigid Mesh Type	Defines the semi-rigid mesh type when slabs are modeled as semi-rigid diaphragms in the sub model. The options are: Quad only Tri only Quad dominant