RF-FORM-FINDING | Results

Compliance with building codes, such as Eurocode, is essential to ensure the safety, structural integrity, and sustainability of buildings and structures. Computational Fluid Dynamics (CFD) plays a vital role in this process by simulating fluid behavior, optimizing designs, and helping architects and engineers meet Eurocode requirements related to wind load analysis, natural ventilation, fire safety, and energy efficiency. By integrating CFD into the design process, professionals can create safer, more efficient, and compliant buildings that meet the highest standards of construction and design in Europe.

In computational fluid dynamics (CFD), complex surfaces that are not completely solid can be modeled using porous or permeability media. In the actual world, examples of such things include windbreak fabric structures, wire meshes, perforated facades and claddings, louvers, tube banks (stacks of horizontal cylinders), and so on.

Windbreak structures are special types of fabric structures which protect the environment from harmful chemical particles, abate wind erosion, and help to maintain valuable sources. RFEM and RWIND are used for wind-structure analysis as one-way fluid-structure interaction (FSI). This article demonstrates how to structural design windbreak structures using RFEM and RWIND.

The results of the form‑finding process are a new shape and corresponding inner forces. The usual results, such as deformations, forces, stresses, and others can be displayed in the RF‑FORM‑FINDING case.

This prestressed shape is available as the initial state for all other load cases and combinations in the structural analysis.

For more ease when defining load cases, the NURBS transformation can be used (Calculation Parameters/Form-Finding). This feature moves the original surfaces and cables into position after form‑finding.

By using the grid points of surfaces or the definition nodes of NURBS surfaces, free loads can be situated on selected parts of the structure.

The form-finding function can be activated in the General Data dialog box, Options tab. Prestresses (or geometrical requirements for members) can be defined in the parameters for surfaces and members. The form‑finding process is performed by calculation of an RF‑FORM‑FINDING case.

Steps of the working sequence:

• Creation of a model in RFEM (surfaces, beams, cables, supports, material definition, and so on)
• Setting of required prestress for membranes and force or length/sag for members (for example, cable)
• Optional consideration of other loads for the form-finding process in special form‑finding load cases (self‑weight, pressure, steel node weight, and so on)
• Setting of loads and load combinations for further structural analyses

After starting the calculation, the program performs form‑finding on the entire structure. The calculation takes into account the interaction between the form‑finding elements (membranes, cables, and so on) and the supporting structure.

The form-finding process is performed iteratively as a special nonlinear analysis, inspired by URS (Updated Reference Strategy) by Prof. Bletzinger / Prof. Ramm. This way, shapes in equilibrium are obtained considering the pre‑defined prestress.

Furthermore, this method allows you to consider individual loads such as self‑weight or internal pressure for pneumatic structures in the form‑finding process. The prestress for surfaces (for example, membranes) can be defined using two different methods:

• Standard method - prescription of required prestress in a surface
• Projection method - prescription of required prestress in the projection of a surface, stabilization especially for conical shapes