How does RFEM efficiently determine the shape of a curved plate structure (compression shell) subjected to compression only?

Answer

The efficiency of a plate structure subjected to compression depends on the shape of it. For each load distribution, there is an associated optimum shape that transfers the loads to the foundations by using as little material as possible.

Figure 01 - Form-Finding of Pressure-Loaded Plate Structure

Since the utilization of a structure usually specifies several load states, it is recommended to align the optimum shape with the main load (permanent load) of the model for purely strategic reasons.

The RFEM program helps you to find these model shapes in conjunction with the RF‑FORM‑FINDING add-on module. The underlying form-finding process shifts the position of the FE mesh nodes in space based on a specified load so that the new position of the elements transfers the load mainly by using the membrane load-bearing capacity. The explicit use of the axial force resistance of members and the membrane force resistance of the surface elements results in constant stress conditions in the cross-sections. This condition with no bending stress utilizes the cross-sections optimally and allows for a very effective structure with the minimum material usage.

This process can be applied to both the usual cable and membrane structures consisting of flexible elements under tension as well as for pressure-loaded rigid beam and shell structures.

To develop an optimum shape of the compression shell in RFEM, proceed as follows:


  1. Activating the RF-FORM-FINDING add-on module in "General Data", tab "Options"
    Figure 02 - Activating Form-Finding Options

  2. Specifying form-finding settings for the structural elements
    Figure 03 - Form-Finding Setting for Beam
    Figure 04 - Form-Finding Setting for Surface Element

  3. Defining the main loading for the form-finding
    Figure 05 - Defining External Form-Finding Loading

  4. Form-finding analysis
The finally developed shape can then be used in RFEM for the structural analysis with regard to the further variable loads.

Keywords

FF Eggshell Form-finding Vault Material usage

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RFEM Main Program
RFEM 5.xx

Main Program

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

Price of First License
3,540.00 USD
RFEM Tensile Membrane Structures
RF-FORM-FINDING 5.xx

Add-on Module

Form-finding of tensile membrane and cable structures

Price of First License
1,750.00 USD