1. Overview
With the rapid advancement of computer hardware and software technologies, computer-aided design (CAD) has made significant strides in the field of architecture. Numerous CAD architectural design programs have entered the market, each based on a unique building entity model and supporting its own data standards. As a result, data exchange and sharing among specialized software have become major challenges in the integration of architectural design technologies.
There are two main approaches to address these challenges:
First, each software can develop its own interface for data exchange and sharing. For example, the 3D3S software from Tongji University Version 0 offers import interfaces for SATWE model files from PKPM software and export interfaces for ANSYS and SAP2000 model files. However, this method does not fundamentally solve the interoperability issues between building models.
Second, the establishment of a truly open international standard for the expression and exchange of building product data is essential for enabling seamless data exchange and sharing. The Industry Foundation Classes (IFC) standard, developed by the International Alliance for Interoperability (IAI), is an ISO standard widely supported by professionals in architecture. This article focuses on applying the IFC standard to automatically generate structural model files from building models.
2. IFC Standards and Revit
The IFC standard defines data related to building and construction engineering. Notably, it is built upon the STEP project, which has a wealth of mature research outcomes, including geometric definitions and core construction engineering models. Leading research based on the EXPRESS data modeling language has been effectively incorporated into IFC, especially in the development of building structural models.
In January 1997, IAI released the first complete version of the IFC Information Model (IFC 1.0). Later, in February 2006, version IFC2x3 (IFC2x version 3) was published. This article uses IFC2x3 as the basis for data conversion.
Major international CAD developers such as Autodesk, Bentley, and Graphisoft have all adopted and support the IFC standard. In this article, Autodesk’s Revit Architecture and Revit Structure software are used to export IFC model files and convert them into structural model files.
Although IFC documentation is fully open, the complexity of the STEP file format and the IFC building model itself makes IFC development challenging. To facilitate development, many companies have created IFC toolkits that provide developers with underlying support platforms, saving time and effort. Commonly used IFC toolkits include the EDM Model Converter from EPM Technology AS, IFC Classic Toolbox from Eur Steps, and the IFC Engine DLL from TNO Environment and Geosciences. This article utilizes the IFC Engine DLL toolkit to extract building model information from IFC files.
3. 3D3S and Structural Model Files
The general format for representing the structural model file in 3D3S is as follows:
1) Annotation:
Comments start with the string $or! or or or /. Please note, no spaces should appear within these comment markers.
2) Define the structural system:
STRU No.
3) Define length units:
UNIT No.
4) Generate nodes:
Format: Node N x y z, where N is the node number and x, y, z are coordinates.
5) Generate elements:
Format: E UnitNumber Node1 Node2
6) Define node constraints:
Format: Con NodeNumber X(0|1) Y(0|1) Z(0|1) RX(0|1) RY(0|1) RZ(0|1)
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