1. Overview
With the rapid advancement of computer hardware and software technologies, the use of computer-aided design (CAD) in architecture has made remarkable progress. Numerous architectural design software programs have entered the market. Although each software is based on its own unique building entity model, they only support their proprietary data standards. This has created significant challenges for data exchange and sharing between specialized applications, posing a major obstacle to integrated architectural design workflows.
Two solutions address these challenges:
First, individual software applications can develop their own interfaces to enable mutual data exchange and sharing. For example, the 3D3S software from Tongji University (Version 0) provides import interfaces for SATWE model files from PKPM software, as well as export interfaces for ANSYS and SAP2000 model files. However, this approach does not fundamentally solve the issue of data exchange and sharing among building models.
Second, the emergence of a truly open international standard for building product data expression and exchange lays the foundation for seamless data interoperability. The Industry Foundation Classes (IFC) standard, developed by the International Alliance for Interoperability (IAI), is an ISO standard widely supported by architectural professionals worldwide.
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 essentially defines building and construction engineering data. It is important to note that IFC is based on the STEP project, which benefits from extensive, mature research results—such as STEP’s geometric definitions and core construction engineering models. The world’s leading research based on the EXPRESS data modeling language can be seamlessly incorporated into IFC. In particular, the development of building structural models within STEP can be effectively utilized in IFC projects.
In January 1997, the IAI released the first complete version of the IFC Information Model (IFC 1.0). Later, in February 2006, IFC2x version 3 (commonly referred to as IFC2x3) was published. This article uses IFC2x3 as the basis for implementing data conversion.
The three major international CAD software developers—Autodesk, Bentley, and Graphisoft—have all adopted and supported the IFC standard. This article specifically uses Autodesk’s Revit Architecture and Revit Structure software to export IFC model files, which are then converted into structural model files.
Although IFC documentation is fully open, the complexity of the STEP file format and the intricacy of the IFC building model make IFC development a challenging task. To assist developers, many companies have created IFC toolkits that simplify the development process by providing underlying support platforms. Popular IFC toolkits include the EDM Model Converter from EPM Technology AS, the IFC Classic Toolbox from Eurostep, and the IFC Engine DLL from TNO Environment and Geosciences. This article is based on the IFC Engine DLL toolkit to extract building model information from IFC files.
3. 3D3S and Structural Model Files
The general format for representing structural model files in 3D3S is as follows:
1) Annotation:
Lines starting with $or!, or, or / indicate comments. Please note that no spaces are allowed within these comment markers.
2) Define the structural system:
STRU No.
3) Define length units:
UNIT No.
4) Generate nodes:
Define node N coordinates x, y, z.
5) Generate elements:
E UnitNumber Node1 Node2
6) Define node constraints:
Con NodeNumber X(0|1) Y(0|1) Z(0|1) RX(0|1) RY(0|1) RZ(0|1)
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