Modelling of Tower with Block Manager
Lattice towers represent typical applications in steel construction. Examples for this special type of truss structures are antenna and overhead line towers, or columns for wind power stations, cable cars, and supporting frame constructions. The modelling can be done individually in RFEM and RSTAB by entering various tower elements. Furthermore, you can use different copy functions and parameterized input options. However, this procedure normally requires considerable effort. It is more comfortable to model such structures using pre-fabricated catalogue elements provided by the Block Manager. Those elements are automatically stored in the database during program installation. Thus, you can use tower segments, platforms, antenna brackets, cable ducts et cetera as parameterized building blocks for generating diverse tower structures.
Specific options to model and design tower buildings are available in the RF-/TOWER add-on modules. But this article describes the modelling of a simple lattice tower with parameterized catalogue elements of the Block Manager. The tower consists of two segments and a platform.
You can open the Block Manager on the menu "File" → "Block Manager" or by clicking the corresponding menu button. The Manager includes various catalogue elements making the modelling of member and surface objects easy.
Tower Segment - Bottom
The following catalogue category is to be defined for the construction in the bottom area of the tower:
"Towers" → "Mast - Segments" → "Rectangular".
Then, you can select type TSR038 in the list to the right.
A double-click on this block type opens the "Insert Block" dialog box.
Lattice towers generally consist of angle profiles. The pre-set cross-sections as well as the material can be adjusted, if necessary (by clicking a cross-section table row you can see in the graphic where it is used in the block). For this example, however, the cross-sections are not modified.
The height of the segment is to be changed to 5.50 m. The adjustment of this parameter is dynamically updated in the graphic.
A base point of the segment is appropriate for the "Insert Point of Block", for example node 6. The number of the node can be selected in the list or defined graphically by clicking the base point. [OK] transfers the model to RFEM/RSTAB.
To select the platform, the Block Manager must be reopened. The following catalogue category is to be specified:
"Towers" → "Platforms" → "For Four-sided Towers" → "Outside Platforms" → "Rectangular"
Then, you can choose type PRR000 to the right.
In the dialog box, the platform parameters a and b must be reduced each to 2.00 m in order to adapt them to the upper dimensions of the previously set segment (see Figure 03). Alternatively, it is possible to take the distances from RFEM/RSTAB: Use the […] button that appears when activating the input field.
The "Global Position of Reference Point" is to be modified to node 1. The number of the node on which the platform should be inserted can be selected in the list or determined graphically in the tower model by using the [Select] button. The platform will be transferred to RFEM/RSTAB by clicking [OK].
Tower Segment - Top
Again, the upper part of the tower structure is created with the Block Manager:
"Towers" → "Mast - Segments" → "Rectangular"
Type TSR035c is to be selected.
Node 2 is to be specified as the "Insert Point of Block". This can be done graphically by clicking the base point in the front.
Again, the "Global Position of Reference Point" is to be set to node 1 of the RFEM/RSTAB model.
The height h must be changed to 4.00 m, the lower distances a2 and b2 to 2.00 m, and the upper distances a1 und b1 to 1.00 m.
After clicking [OK] the tower model looks like in Figure 08.
When combining the blocks, it is possible that nodes with identical coordinates are created. To clean the model, a corresponding check should be carried out.
"Tools" → "Model Check" → "Identical Nodes"
Nodes lying upon another are shown in the "Identical Nodes" dialog box. The dialog box also allows you to unite these nodes.
Finally, the tower model can be extended by other catalogue elements such as antenna brackets, cable ducts, cross beams, or bracings. These building blocks are stored with parameters, too.
Lattice towers can be easily modelled by means of parameterized catalogue elements of the Block Manager. The library of the system components is also extendable by user-defined specifications so that variations of recurring models can be quickly created by using blocks.
Alternatively, you can use the possibilities offered by the various RF-/TOWER add-on modules, developed for the planning and design of towers. They also allow you to determine specific requirements of load application. The RF-/TOWER modules are presented in a webinar.
Dipl.-Ing. (FH) Robert Vogl
Technical Editor, Product Engineering & Customer Support
Mr. Vogl creates and maintains the technical documentation. In addition, he is involved in the development of the SHAPE-THIN program and provides customer support.
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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements
The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions