
==== Front
Sci Rep
Sci Rep
Scientific Reports
2045-2322
Nature Publishing Group UK London

72497
10.1038/s41598-024-72497-7
Article
Research on information extension of mountainous rack railway engineering based on IFC standard
Yang Yongyi 1
Li Jinsheng jinshengli@stu.xhu.edu.cn

1
Zhang Zizhen 2
Liu Yanming 3
1 https://ror.org/04gwtvf26 grid.412983.5 0000 0000 9427 7895 School of Emergency Science, Xihua University, Sichuan Province, Chengdu, 610039 China
2 Kunming Atide Software Co., Ltd, Kunming, 650106 Yunnan China
3 https://ror.org/00hn7w693 grid.263901.f 0000 0004 1791 7667 School of Civil Engineering, Southwest Jiaotong University, Chengdu, 610031 Sichuan China
16 9 2024
16 9 2024
2024
14 2155720 5 2024
9 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
In response to the practical demands for data sharing and exchange in the field of rack railway systems engineering, as well as to address the gaps in the rack railway domain within the framework of the IFC4 standard, we extend and define the rack railway domain through entity extension and custom attribute sets. By utilizing the ongoing construction of the Dujiangyan to Mount Siguniang Railway as a case study, we validate the utility of this IFC extension and modeling approach. Leveraging IfcOpenShell, we incorporate the extended data content into the generated IFC file. We present a process for extension tailored to the characteristics of rack railway engineering. This study aims to provide broader information support for the digital construction of track structures in the design phase of rack railway engineering and to facilitate more efficient data exchange and sharing.

Keywords

IFC standard
Entities
IFC extension
Rack railway
Data exchange
Subject terms

Civil engineering
Information technology
issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

In comparison to conventional railways, rack railways incorporate an additional rack rail track in the middle of the track, along with gear mechanisms on railway vehicles that can engage with the rack rail. This engagement between gears and rack rail provides greater traction and braking force for locomotives when climbing slopes, addressing the reliability issues associated with relying solely on friction for locomotive propulsion and braking on traditional railways. Rack railways are primarily suitable for applications such as mountain railways, scenic tourist railways within attractions, tourist special trains, transportation lines connecting different tourist attractions, and connecting lines between urban transportation hubs and tourist attractions. These railways play a crucial role in promoting tourism development and the socioeconomic progress of western mountainous regions. As shown in Fig. 1, the on-site images depict the formation of the rack railway line and the testing of the train.Fig. 1 On-site images of the formation of the rack railway line and the testing of the train.

In comparison to conventional railways, rack railways incorporate a gear rack system, which is utilized in steep gradient sections where adhesion between steel wheels and rails is insufficient to meet climbing requirements. Figure 2 illustrates a cross-section sample of the rack system.Fig. 2 Rack system cross-sectional sample.

Railway engineering is a comprehensive discipline that involves integrating designs of railway tracks, rails, switches, embankments, and other components. Additionally, it requires coordinating with station infrastructure such as buildings for integrated design1. As depicted in Fig. 2, this cross-section includes various components and facilities such as rack rail steel tie fastenings, running rails, rack rail tracks with ballast track beds, and rail expansion adjusters. With the rapid development of modern transportation, there is a need to accelerate the construction of an integrated transportation system, with highways and national railways as the main arteries supplemented by mountainous rail transit. Leveraging its unique advantages, rack railways, as a new type of rail transit system, are expected to have significant development and application prospects within China's mountainous rail transit system. Due to these characteristics, modeling mountainous rack railway systems is more complex compared to conventional railway track designs (e.g., monorails, light railways), requiring greater attention to detail.

Compared to the manufacturing industry, which has largely completed its informatization and is gradually moving towards intelligence, China's rail transportation industry has yet to achieve overall industrialization but is already facing opportunities and challenges in terms of informatization and even intelligence transformation2. The technology of Building Information Modeling (BIM) has been widely applied in rail transportation3, significantly driving the informatization and intelligence transformation of the industry. However, the level of intelligence still lags behind that of the manufacturing industry. Therefore, in addition to achieving digitization and informatization, the BIM modeling process in mountainous rack railway transportation is considerably more complex compared to conventional railway engineering.

During the BIM modeling process, factors such as data interoperability, model accuracy, collaboration, standardization, and lifecycle management are crucial. Among these, data sharing and exchange pose common challenges across various domains of BIM application4. To address this issue, buildingSmart International introduced the Industry Foundation Classes (IFC)5, in 1994, a standard known for its scalability6, used to represent components in many civil engineering fields7. Therefore, utilizing IFC entities as a foundation to describe necessary structures and key components of railway stations, including rack railways, is appropriate. In fact, a series of IFC entities has already been extended to describe railway-related elements8. However, despite the existence of some entities related to railway engineering information modeling, the current IFC still cannot comprehensively encompass the hierarchy and semantic information of mountain rack railway systems (MRRS) due to the uniqueness and characteristics of rack railways. Considering the significance of MRRS in railway engineering systems, there is a substantial gap in BIM data standards for key structures in the rack railway domain, such as traction devices, hindering their relevant applications.

To address or enhance the aforementioned issues, this study proposes an IFC extension to describe mountain rack railway systems (MRRS), aiming to facilitate the application of BIM in rack railway design. Research on mountainous rack railways based on BIM technology involves interdisciplinary applications. To achieve the goal of extending IFC for MRRS, the work of this study is primarily divided into three parts, focusing on aspects such as the overall architecture of IFC, types of IFC entities, and mechanisms for IFC extension, tailored to the characteristics of rack railway systems.

The remaining content is organized as follows: Sect. “Related work” analyzes existing literature and summarizes the identified problems. Section “Research on BIM extension of mountain gear rail based on IFC standard” begins by elucidating the application and characteristics of BIM technology in rack railway systems. It then proceeds to extend and define the rack railway domain through entity extension and custom attribute sets. Section “Expansion and expression of rack solids based on IFC standard” introduces the modeling methods in 3DEXPERIENCE (Version: R2021x) and how this platform can be utilized to achieve the extension of IFC for conducting case studies. Section “The extension of the rack IFC via the 3DE platform is used for model fusion” demonstrates the modeling results of MRRS, rack railway guiding equipment (RRGE), etc. Section “Conclusion” concludes the contributions of this method and discusses potential future research directions.

Related work

Research status and development trends

BIM integrates structured, multidisciplinary data into intelligent models supported by remote platforms, generating a digital representation of an asset throughout its entire lifecycle, from planning and design to construction and operation.

BIM technology plays a crucial role in improving the engineering design level of the railway industry. Leveraging the information modeling capability of BIM technology during the railway engineering design phase to achieve digital transmission of design information is a challenge in the application of BIM technology in railway design. Utilizing the industry foundation classes (IFC) standard to integrate railway structural engineering information into BIM models is an effective approach to overcome this challenge.

Barnabas et al.9 conducted a detailed study on the route characteristics and structural features of rack railways. Chen et al.10 discussed the dynamic effects of two common types of rack connections (rigid and flexible connections) on the adaptability and safety of the system. Chen, Z. W. et al.11 developed a detailed vehicle-chassis (rail)-bridge coupled dynamics model. Subsequent field experiments were conducted to obtain the basic dynamic characteristics of rack rail tracks and to validate the established numerical model. In summary, a unified data flow enables the export of geometric and attribute information from the established BIM model to formats supported by mechanical analysis software such as ANSYS (Version:2023R1), ABAQUS(Version:2022), and SolidWorks(Version:2021SP5).The mechanical analysis software is then used for mesh generation and boundary condition setting. After running the analysis, the results are visualized and validated, providing feedback to optimize the design. This process ensures efficient and accurate mechanical behavior simulation and evaluation, offering robust technical support for the successful implementation of engineering projects. He Qing et al.12 addressed the inadequacy of information on layer entities in the IFC standard architecture by utilizing entity extension and custom attribute sets to extend and define the railway domain. In terms of entity extension, it encompasses the expansion of spatial structural units, assemblies, components, and parts. Custom attribute sets, on the other hand, extend identity information, location information, and technical information13. Building upon this foundation, a further modeling method tailored to railway structural BIM models is proposed.

Ontology is a formal method of knowledge representation in the field of computer science, used to describe entities in the real world and the relationships between them14,15. The goal of an ontology is to provide a shared and consistent conceptual framework, enabling computer programs to understand and process information, thereby facilitating information sharing and semantic interoperability16. The ontology types for mountainous rack railways depend on specific ontology modeling requirements and usage scenarios. A common approach is to use specific metalanguages or ontology languages (such as OWL or RDF)17 to describe the concepts, properties, and relationships of mountainous rack railways.

Railway infrastructure ontology: Defines the infrastructure components of rack railways18, including track layouts, switches, signals, and station facilities.

Topographic ontology: Describes the topographical features and terrain characteristics relevant to mountainous areas where rack railways are built.

“Topographic ontology” is a concept that involves geographic information systems (GIS), building information modeling (BIM), and other related fields. It typically refers to data models or methodologies used to describe and represent topographical features. This ontology encompasses the shape, characteristics, and attributes of terrain, facilitating effective information exchange and sharing between different systems and applications.

As illustrated in Fig. 3, the three-dimensional terrain model highlights the track routes superimposed on the topography. It clearly presents the terrain undulations and the trajectory of the railway lines. Considering the impact of irregularity parameters such as track curvature, gradient, and unevenness, it integrates data from geological, civil, and mechanical engineering to Intuitively reflect the track irregularity.Fig. 3 Digital terrain model. (a) Partial (b) overall terrain. (This topographic map was generated by InfraWorks software. Version 2023, URL: https://www.autodesk.com.cn/products/infraworks/overview?term=1-YEAR&tab=subscription).

The application of IFC in railway engineering

IFC stands for industry foundation classes19. It is an open, structured, object-based information exchange standard format developed on the basis of the STEP standard20.

The latest version currently is IFC421. Therefore, this study is based on IFC4. The railway engineering information modeling data storage standard extends the concepts in the railway domain through static and dynamic extensions, as illustrated in (Fig. 4).Fig. 4 Railway engineering information model data storage standard extended frame diagram.

In the IFC model, static extension refers to adding definitions of railway entities to the IFC Schema. These additional entities are hierarchically defined based on the object-oriented inheritance principle to describe various elements in railway engineering. The result of this extension is the generation of EXPRESS schema files22. By parsing EXPRESS files, software development can identify railway IFC objects.

The IFC specification provides detailed definitions of entities, relationships, and properties in the railway domain. This specification can be represented in HTML, EXPRESS, XSD/XML, and OWL formats23, with EXPRESS being the most commonly used format. In the EXPRESS format, entities, relationships, and properties are represented by entities in the exp. file, which is editable to facilitate extensions.

Dynamic extension refers to expressing standardized railway domain information by setting specific field data on existing IFC entities, without modifying the IFC Schema. This method can be used to label and identify railway engineering information models24.

Liu et al.25 argue that IFC provides both the semantics and geometry of facilities, allowing for the easy derivation of the topological relationships between elements. Researchers can further explore the vertical dimension of 3D geometries in IFC to facilitate the conversion from IFC to standardized models and utilize IFC to manage real-time data, reflecting morphological changes. Thomas F26 conducted a thorough analysis of the IFC standard, studying its scope extension, data exchange, and model interoperability aspects. Kim27 developed a data file converter with standardized data formats and access methods based on the IFC standard. In the field of railway engineering, the primary application of IFC focuses on the information model for shared data, facilitating design and maintenance tasks. Chen et al.28 performed IFC extensions to share and store maintenance tasks not provided in the current IFC version. Integration of BIM data with facility management databases enables automatic scheduling of maintenance tasks, greatly facilitating daily scheduling work. The track is one of the most crucial components in railway engineering. Tae Ho Kwon et al.29 introduced a method based on extending Industry Foundation Classes (IFC) for creating three-dimensional aligned railway track models. This method utilizes AMT alignment tools and IFC STEP tools to create track shapes by manipulating control points of NURBS curves. In railway engineering, the integration of multi-source data and high-precision modeling of bridges and tunnels in high-altitude and complex terrain areas enables refined management throughout the entire project lifecycle. Lee et al.30 proposed a semantic generation method based on component information in industry foundation classes (IFC), defining information items required for semantic recognition and categorizing components of steel box girder bridges. Wu19 discussed the development of data integration and sharing in geotechnical engineering information modeling based on IFC, as well as proposing an information modeling method based on IFC extension. Park and Lee et al.31 introduced a meshless analysis method for studying bridge structures and extended corresponding IFC entities representing bridges and meshless entities. Zhou Ying et al.32 verified a newly developed IFC extension by demonstrating successful conversion from a parametric design model of tunnels to a segment assembly system. Providakis, S., et al.33 extracted engineering parameter information related to risk factors from BIM files of specific projects. They used the IFC standard as a bridge between BIM data and MATLAB for mesh generation and analysis tools to assess the safety risks of tunnels. In terms of operation and maintenance, as well as hazard identification. Sara Ait-Lamallam et al.34 proposed a method to extend the IFC standard to the operation and maintenance management of road infrastructure, realized through OpenBIM. The IFCRoad standard serves as the foundational standard for applying OpenBIM in the road infrastructure field35, including managing O&M business processes and software implementation. Linlin Kong et al.36 presented a method for embedding fire emergency management process knowledge into BIM by extending industry foundations and embedding knowledge. Taking fire emergency management based on BIM as an example, fire emergency management process information is embedded into BIM through the form of knowledge expert modeling and credibility verification.

However, while the aforementioned studies have filled gaps in most areas of the IFC standard, the extension research within the railway domain remains limited. The related content still needs to be further refined, and there is currently a lack of extension in the specific domain of rack railways, which requires further development.

In summary, the current research on BIM collaborative design in the railway industry is relatively weak. The existing track BIM models are difficult to standardize and fail to address data sharing challenges across different lifecycle stages. Creating railway BIM models sometimes requires reverse engineering, resulting in suboptimal BIM modeling efficiency and quality. Therefore, further research is needed on the application of railway BIM parametric modeling technology in mountain rack railway systems, forward design patterns, and the efficient transfer of data models. The aim of this study is to extend the latest IFC standard to fill in and refine the foundational data framework of mountain rack railway systems and to explore convenient and effective methods for rack railway modeling.

Semantic model of MRRS

In this section, an IFC extension for describing the Mountainous Rack Railway System (MRRS) is proposed. The IFC schema is extended according to the needs of railway engineering, addressing the lack of domain-specific entity information within the IFC standard architecture. This is achieved through entity extensions and the definition of custom property sets for the rack railway domain. Consequently, a foundational data framework for the rack railway structure is established. By extending entity relationships and utilizing the IFC standard expression mechanism, a system for expressing newly added rack railway entities and attribute sets is constructed. This forms a railway-specific IFC standard, which can facilitate BIM-based railway engineering construction management.

The railway-specific IFC standard enables the transfer of construction model information to the construction management platform, facilitating information exchange and application across various stages. In addressing the challenges of data sharing among multiple disciplines and stakeholders, and the inconsistency of models across different phases of the project lifecycle, the IFC standard's description of entity property sets and their relationships can be analyzed. This provides a data foundation for infrastructure status identification during the lifecycle operation and maintenance phase.

Salient features of the MRRS

Based on the structure and characteristics of rack railways, both the Dujiangyan to Mount Siguniang demonstration line and the Ziyang test line currently adopt a rack structure similar to the Von Roll rack. The track bed structure utilizes ballast track beds, with design parameters still referencing traditional railway design standards. The shoulder width of the track bed is 400 mm, the ballast height is 250 mm, and the side slope is 1:1.75. The rack structure is laid in the middle of the track sleepers, as shown in (Fig. 5). (a) depicts the main view of the assembled non-hole rack rail steel sleeper fasteners, while (b) illustrates the side view of the rack railway track under simple beam action.Fig. 5 (a) Rack rail assembly and configuration steel sleeper diagram; (b) Side view of the cog railway track under the action of simple support beam.

Considering limited processing capabilities, the racks typically use short racks, each measuring 2.4 m in length. The 3D shape of the rack is depicted in (Fig. 6a), with joints being fixed using L-shaped plates and bolts, as illustrated in (Fig. 6b). Figure 6c shows the state of the rack when bent. The specific parameters of the rack are detailed in (Table 1).Fig. 6 (a) Conceptual model; (b) Rack joint connection fastener; (c) Rack curvature diagram.

Table 1 Design value of rack parameters.

Project	Value	Project	Value	
Modulus	100/pi	Pressure angle	14.032°	
Coefficient Of addendum	0.75	Coefficient Of top clearance	0.25	
Material	42CrMo	Hardness	30HRC	
Tooth width	60 mm	Single section length	2.4 ~ 3 m	
Accuracy	Level 8–10	Corrosion protection level	Level 9	

Research on BIM extension of mountain gear rail based on IFC standard

IFC standard data architecture

In each level of the IFC standard architecture, there are typically five basic elements comprising it. Table 2 presents the distribution of elements for each level. Table 2 Distribution of elements at all levels of the IFC standard framework.

	Type	Entity	Function	Rule	Properties	Quantity set	
Domain layer	102	198	0	0	276	69	
Share layer	40	100	0	0	90	16	
Core layer	19	64	3	1	2	0	
Resource layer	214	333	45	1	17	0	
Summation	375	695	48	2	385	85	

IFC extension mechanism

In an IFC file, any entity (such as IfcBeam) is described through its attributes, which can be categorized into direct attributes, derived attributes, and inverse attributes. Direct attributes represent scalar quantities or direct information, such as Global Id and Name. Derived attributes are properties described by other entities, such as OwnerHistory, ObjectPlacement, and Representation. Inverse attributes are properties linked through associated entities, such as the association of material information for components through the HasAssociations property, linked via the IfcRelAssociates entity. In a physical IFC file, the IfcBeam statement only displays 9 attributes, including both direct and derived attributes, while the remaining 24 attributes are inverse attributes. Figure 7 illustrates the relationship between direct and derived attributes.Fig. 7 Representation of direct and exported properties.

In terms of vertical layering, the railway engineering information model can be divided into four levels: existing IFC entity classes, extended railway IFC entity classes, predefined types of extended railway IFC entity classes, and classification and coding of railway engineering information models. These levels can be expanded and defined based on the specific requirements and elements of railway engineering.

In terms of horizontal layering, the railway engineering information model can be categorized into five types: spatial structural units, components, parts, assemblies, and systems.

Additionally, IFC utilizes properties (Property) and property sets (PropertySet) to express the characteristics of IFC entities. Through property set definition (PSD) XML description language, properties of railway engineering information model entities can be defined and exchanged within IFC. This ensures data consistency and interoperability between different systems and software.

Data structure of railway engineering information model

The foundational data structure of the railway engineering information model is an extension of the IFC architecture tailored to the requirements of railway engineering, as depicted in (Fig. 8). Within the geometric resources layer, partial definitions of rack components are added. In the core layer’s product extension, the IFC rack class is expanded to represent rack sections of railway tracks. The Interop Layer incorporates definitions of shared modes for railway engineering, including common components and property sets. In the Domain Layer, this study focuses on expanding the domain of railway track and rack infrastructure.Fig. 8 Basic Data architecture of railway engineering information model.

The entity inheritance relationships of the railway engineering information model are illustrated in (Fig. 9). Embankments, bridges, tunnels, tracks, and stations are extended by defining corresponding spatial structural units, components, assemblies, and parts. Entity definitions include spatial structural units, components, assemblies, parts, alignment of track centerlines, and systems.Fig. 9 Railway engineering information model entity inheritance.

For spatial structural units, begin by deriving the Civil Engineering Spatial Structure (IfcCivilStructureElement) class from the IfcSpatialStructureElement class in the IFC standard. For the railway-specific domains of tracks and stations, begin by deriving the Railway Engineering Spatial Structure (IfcRailwayStructureElement) class from the Civil Engineering Spatial Structure. Then, under the Railway Engineering Spatial Structure, further derive the spatial structures for rack (IfcRack), track (IfcTrack), and station (IfcRailwayStation).

For components, For tracks and stations, begin by deriving the Railway Element (IfcRailwayElement) class from the IfcCivilElement class. Then, further derive specialized components for each discipline.

For assemblies, For tracks, begin by deriving the Railway Assembly (IfcRailwayAssembly) class from the IfcCivilElementAssembly class. Then, further derive track assemblies.

For parts, Derive the Railway Element Component (IfcRailwayElementComponent) class from the IfcCivilElementComponent class for railway components. Then, derive the Track Element Component (IfcTrackElementComponent) class from the Railway Element Component class for track components.

The composition of railway engineering spatial structures is illustrated in (Fig. 10). A railway project (IfcProject) may encompass one or multiple railway lines (IfcRailway) and one or several railway terminals (IfcRailwayTerminal). Each railway line (IfcRailway) may comprise one or multiple tracks (IfcTrack) or racks (IfcRack). The railway terminal (IfcRailwayTerminal) can also include a series of railway lines (IfcRailway) and railway stations (IfcRailwayStation).Fig. 10 Composition of spatial structure in railway engineering engineering.

Expansion and expression of rack solids based on IFC standard

Rack field mode

This pattern defines the basic data architecture of the railway track and rack engineering domain information model. Railway track engineering includes the mainline and siding tracks with ballasted and non-ballasted track structures and their components.

The basic data architecture of the track information model consists of four types: spatial structure elements (IfcSpatialStructureElement), assemblies (IfcElementAssembly), components (IfcElement), and parts (IfcElementComponent).

Taking the 5–7# turnout in the experimental line project as an example, this type of turnout component includes switch rails, frogs and guard rails, steel rails, joint fishplates, joint bolts and nuts, flat washers, rail gauge blocks, joint gauge blocks, rail pads, and height adjustment pads. The switch rail is a device used to control the direction of the turnout, allowing trains to pass smoothly through the turnout area and ensuring that they travel along the designated route or direction. Turnouts consist of switch rails, stock rails, and the associated switch ties. Figure 11 illustrates the interrelated relationships between the turnout component units.Fig. 11 Correlation diagram between switch component units.

The spatial structure units of the track refer to the spatial main body of the track structure and its main constituent structures. They are divided into tracks (IfcTrack) and track segments (IfcTrackPart), racks (IfcRack), and rack segments (IfcRackPart). Based on this, the inheritance and derivation relationships between the spatial structure units of the track are extended as shown in (Fig. 12).Fig. 12 Express-G diagram of the extended cog track space structural unit.

The rack (IfcRack) is a special gear with teeth distributed along a strip-like body. Racks can be categorized into straight-toothed racks and helical-toothed racks, which are respectively paired with spur gears and helical gears. The IfcRack can consist of one or multiple instances of IfcRack, or it can be composed of one or multiple segments of IfcRackPart.

The IfcRackPart refers to a segment composing the IfcRack, possessing a unique type of rack guide rail structure and functional type. The IfcRackPart should be contained within the IfcRack.

Mountain rack track members

The track components mainly include: IfcTrackRail, IfcTrackFastening, IfcTrack-Sleeper, IfcTrackSlab, IfcTrackAdjustmentLayer, IfcRackBase, IfcRackTurnout IfcRackBallastLayer, IfcRackWedgeTypeLockWashers, IfcRackBolt, and so on. The in-heritance relationship between track component units is shown in (Fig. 13).Fig. 13 Express-G diagram of the extended rack track member.

Mountain rack railway track assembly

The track assemblies refer to combinations of components within the track structure that serve specific functions. They include ballast bed (IfcBallastBed) and track panel (IfcTrackPanel), as well as the rack panel (IfcRackPanel) at the same hierarchical level extension. The inheritance relationships between track assembly units are depicted in (Fig. 14).Fig. 14 Express-G diagram of the track assembly.

The rack panel (IfcRackPanel) for rack segments is a structural component formed by connecting each section (two rails) of steel rails and sleepers with fastenings. The rack panel assembly (IfcRackPanel) can be composed of steel rails (IfcRackRail), fastenings (IfcRackFastening), and sleepers (IfcRackSleeper). IfcRackPanel should be included in IfcRackPart and can be contained within IfcRack.

Rack part body

Components of rack railway tracks refer to small objects attached to or included within track components, serving auxiliary functions such as reinforcement or connection. They mainly include rail joints, track reinforcement devices, and track accessories. The inheritance relationship between rack railway track components is shown in (Fig. 15).Fig. 15 Express-G diagram of track parts.

The rack rail joint refers to the connecting component used at the joint between rack rails. The IfcRackRailJoint is included within the IfcRack. Track reinforcement equipment is installed on the track to enhance the resistance of the rails to longitudinal and lateral movement. Through predefined type attributes, track reinforcement equipment is further subdivided into items such as anti-creepers, anti-creep struts, gauge tie rods, and rail braces. Track accessories are devices installed on or beside the track to provide specific effects such as sealing, protection, and adhesion. Through predefined type attributes, track accessories are further subdivided into items such as sealing strips between sleepers, steel spring vibration isolators, rubber damping pads, sound-absorbing panels, and guardrails. As shown in Table 3, the predefined types of rack rail component extensions. Table 3 Extension table for predefined types of rack rail parts.

Parent parts	Subclass parts	IFC Entity	
Predefined type attribute rack reinforcement equipment	TICREEPER	IfcTicreeper	
ANTICREEPSTRUT	IfcAnticreepStrut	
GAUGETIEROD	IfcGaugeTierod	
RAILBRACE	IfcRailBrace	
Predefined type attribute rack attachment equipment	SEALINGSTRIPBETWEENSLEEPERS	IfcSealingStripBetweenSleepers	
STEELSPRINGVIBRATIONISOLATOR	IfcSteelSpringVibrationIsolator	
RUBBERDAMPINGPAD	IfcRubberDampingPad	
GUARDRAIL	IfcGuardRail	

Extension and expression of rack solid property set based on IFC standard

The “international framework for dictionaries” (IFD) based on the ISO 12006-2 framework provides a clear and reliable classification and coding system for defining unique type codes for every concept and term in the railway domain. This standard categorizes railway engineering components into five levels based on their functionality, form, work items, and products, ensuring information parity and hierarchical clarity. Building upon actual production activities and static extension methods as the benchmark, further entity extensions in the railway track domain are performed according to the IFD standard. Consistent definition approaches are adopted at each level, with nested hierarchical relationships established to construct track component units. Additionally, to ensure that the information of the toothed rail model at the design stage still meets the corresponding requirements during the operation and maintenance stage, it is systematically expanded from four levels: spatial structure units, assemblies, components, and parts. The inheritance relationships at each level after expansion are depicted in (Fig. 16).Fig. 16 Rack rail information model Ifc extended express-G diagram.

Entities in railway engineering are derived from subclasses of the IfcProduct entity. Among them, the RailwayStructureElement (IfcRailwayStructureElement) is used to organize all spatial structural elements in the railway domain, derived from the SpatialStructureElement (IfcSpatialStructureElement). Based on this, the categories of Rack (IfcRack) and RackPart (IfcRackPart) are derived. The Track entity is used to describe a complete track with full structure and functionality, while the TrackPart entity is used to describe a part of the track with certain structure and functionality (such as the segment containing the toothed device in the rack). There is a whole-part relationship between the track and track part, associated through the IfcRelAggregates relationship entity.

The extension of the rack IFC via the 3DE platform is used for model fusion

The IFC extension proposed in this study aims to leverage the object-oriented capabilities of IFC in AEC to appropriately model MRRS's BIM model. Figure 17 illustrates a series of modeling processes and data flows between software tools.Fig. 17 The process of modeling the corresponding data flow between MRRS and software tools.

The key technical aspect in this chapter is to establish a unified data description based on the IFC extension mechanism and leverage the 3DE platform to realize the definition of BIM object data for mountain rack railways. To build the BIM model for rack railways, it is essential to define classes for rack railway objects and establish a unified data description based on the IFC extension mechanism, laying the foundation for subsequent model integration.

The 3Dexperience (Version: R2021x) platform is a unified digital design environment that supports engineering design, analysis, and management across various domains. Especially in complex domains like railway engineering, standard IFC modeling may not fully meet the needs of design and management. Therefore, further extension and definition are required.

The TXO module on the 3DExperience platform is specifically designed for data management and services, enabling efficient handling and manipulation of IFC model data. Additionally, the dmc tool facilitates the extension and definition of IFC models. By leveraging the TXO module and dmc tool, comprehensive definition and deployment of IFC models can be achieved, thereby enabling broader applications in the railway track domain.

Following the steps outlined in Fig. 18, the entire definition and deployment process of the extended IFC, as described in Chapter 3, can be carried out based on the 3DExperience platform using the TXO module and the dmc tool. Finally, the data, along with semantic information, can be written into the IFC file using IfcOpenShell. In this study, IFC plays a crucial role in addressing interoperability issues among different software tools. The semantic and geometric information expressed by the extended IFC can be shared and utilized for further processing and analysis by other tools that support the IFC format.Fig. 18 Extend the 3DE platform IFC object to define the deployment workflow.

The generated IFC file can be imported into Open IFC Viewer (Version: 24.3.0) and usBIM (Version: 1.0.0.0) to obtain the display results shown in (Figs. 19 and 20), respectively. Open IFC Viewer and usBIM offer convenient functionalities for browsing and viewing IFC files, enabling easier editing and analysis.Fig. 19 Open IFC viewer rack segment display model. (This diagram was generated by Open IFC Viewer. Version 24.3.0, URL: https://openifcviewer.com/), and then we further processed it using PowerPoint.

Fig. 20 The usBIM tooth rail entry device segment shows the model. (This diagram was generated by usBIM. Version 1.0.0.0, URL: https://www.accasoftware.com/en/ifc-viewer).

Case study

The purpose of this chapter is to showcase the modeling results obtained using IFC extensions and viewers. Importing the IFC file into Open IFC Viewer enables the con-struction of a 3D BIM model for MRRS, establishing geometric representations and semantic information attached to the resulting model. The demonstration focuses on selecting a segment of the Chengdu-Chongqing Railway as an example.

Overview of the case and modeling result

This case study is based on the ongoing construction of the Dujiangyan to Mount Siguniang Railway line in China, depicted in (Fig. 21). The Dujiangyan to Mount Siguniang project represents China’s pioneering mountainous railway transportation project employing a combined rail system of conventional and rack rails. It marks the beginning of a new era in the development of standardized railway transportation in Sichuan Province and even across China, significantly contributing to the coordinated development between the Chengdu Plain Economic Zone and the Northwestern Sichuan Ecological Demonstration Area. With a total length of approximately 123 km, the railway utilizes a dual-mode traction system with conventional steel rails and rack rails on steep gradients, as illustrated in (Fig. 22). This necessitates the use of rack rail entry devices, as shown in (Fig. 23), to facilitate the transition onto steep gradients. The modeling results of the entry device are chosen for the case study analysis.Fig. 21 Site map of dujiangyan irrigation project siguniang mountain railway line.

Fig. 22 On site construction drawings for the Dapo road section.

Fig. 23 Overview of the BIM model of the inlet section of the Dusi railway station: (a) IFC an-notation of the ingress, synchronization, correction device (b) modeling results in AutuoCAD (c) modeling results in composer.

Multi-component matching IFC result display

Faced with complex mountainous terrain and geological conditions, the construction of rack railways will traverse valleys and mountains in the form of bridges and tunnels. The track alignment follows the terrain undulations. High-precision parametric modeling will be employed to create adjustable parametric track components that can account for track irregularity parameters (such as curvature, gradient, and unevenness). Utilizing BIM technology, a detailed digital model encompassing terrain, structures, and other elements will be developed. This model will facilitate scenario studies and assist in route planning through simulations. As shown in Fig. 24, the track design types along the rack railway section of the bridge are illustrated.Fig. 24 (a) Rack railway track (b) Along the rack railway line. (This graphic was generated by InfraWorks software. Version 2023, URL: https://www.autodesk.com.cn/products/infraworks/overview?term=1-YEAR&tab=subscription).

As the disciplines of bridge, tunnel, and rack rail in the Dujiangyan to Mount Siguniang mountainous rack rail transportation project are refined, it has been discovered that the allowable variation in rack rail pitch should not exceed 3 mm due to the elastic attenuation of ballast and track fastening components. Whether the rack rail pitch can meet operational safety requirements and whether necessary measures need to be taken are key concerns in the engineering design. Additionally, in response to the adaptability measures for rack rails on ballasted tracks, especially on long steep gradient sections and along infrastructure such as bridges, domestic scholars have proposed the structure of rack rail fixed connecting components. These components involve opening elongated holes in the bottom plate or side plate of the rack rail L-shaped connectors. When relative expansion or contraction occurs between the rack rail and the bridge, the rack rail and fastening components can longitudinally expand or con-tract, ensuring the fixed longitudinal pitch of the rack rail. The detailed modeling results of this description are illustrated in (Fig. 25).Fig. 25 Rack L-shaped connector IFC expression.

The Rack Railway Guiding Equipment (RRGE) is a crucial component on rack rail lines, designed to connect the wheel-rail driving section with the rack-rail driving section, ensuring synchronous rotation between the gears and the rack to prevent potential safety issues such as tooth impact and shock. The RRGE mentioned in this paper adopts a three-section structure, including the synchronization device, the tooth engagement device, and the correction device, as shown in (Fig. 26). The synchronization device gradually increases the speed of the gear on the vehicle to match the vehicle's speed; the tooth engagement device further adjusts the angle of the gear rotation to reduce meshing impact; while the correction device ensures correct engagement between the gear and the rack and transfers driving force. The performance of the RRGE directly impacts the smooth operation and safety of rack rail trains. Scientific and rational modeling design is of great significance for improving the tooth engagement effect of the guiding equipment, reducing tooth engagement impact, and ensuring safe operation. Figures 27, 28 and 29 intuitively display the IFC files of the rack rail synchronization device, tooth engagement device, and correction device. Figure 30 depicts the IFC information description of the transition joint from tooth engagement to correction of the rack rail, as shown.Fig. 26 Examples of correlation between tooth insertion device, synchronization device, cor-rection device and tooth rail components.

Fig. 27 IfcRackRailSynchronizationDevice part.

Fig. 28 IfcRackRailEngagementDevice part.

Fig. 29 IfcRackRailAlignmentDevice Part.

Fig. 30 IFC representation of the connecting part from the rack entry to the correction transition.

The results indicate that in this study, IFC played a crucial role in addressing interoperability issues between different software tools. The extension of the IFC Rack class to represent the rack railway sections, as well as the addition of shared schemas and common property sets for railway engineering at the shared and domain-specific levels, ensured that all information regarding the rack railway system could be accurately described within the IFC standard. The geometric and semantic information defined by the proposed IFC extensions can be shared and utilized for further processing and analysis by other tools supporting the IFC format. This achieved compatibility with the rail transit BIM model and ensured the seamless transfer of data models.

Conclusion

To promote the development of digitalization in railway engineering and enhance the efficiency of information conversion and data sharing during the BIM model design phase, this paper extends and defines the mountain rack rail railway traffic structure based on the IFC standard. The focus is on entity extension and custom property sets, thus forming a rack rail engineering basic data system based on the IFC standard and creating a rack rail track structure with a semantic model. This study not only fills the gap of the MRRS in the IFC standard but also provides a well-defined IFC standard. This is of great significance for promoting digital transformation in the rack railway engineering field and paves the way for sustainable development and innovation in related industries. The main conclusions are as follows:The method proposed in this paper for extending IFC entities is feasible. The rack railway IFC standard developed based on this research enables data sharing, integration, and interoperability of rack railway BIM models across different software platforms. Additionally, users can customize or add IFC entities in the configuration file as needed, mapping IFC entities to software API classes to more accurately represent entity information in the rack railway domain and reduce modeling time.

A method for defining mountain rack railway model information based on the extension of the IFC standard is proposed. A unified data description was established based on the IFC extension mechanism, and the definition of mountain rack railway BIM object data was achieved using the 3DE platform. Through related work, it has been found that adding new entity types within the framework of the EXPRESS language enables the representation of these new entities within the inheritance hierarchy of the IFC standard.

The widespread adoption of the IFC standard requires enhanced support from various professional software. Although the IFC standard has established a relatively comprehensive system of object classes, achieving a complete description of all data and information throughout the building lifecycle necessitates continuous expansion and refinement. This task requires the collaborative effort of all sectors within the civil engineering industry. With the advancement of information technology in the civil engineering sector, new facilities and equipment will continually emerge. The attribute information of these objects should be promptly updated in the IFC standard to ensure it remains a practical international standard.

Due to the limitations of related work and other factors, the plan for the next step is to conduct research on defining the content of a semantic model that includes relevant constraints and other necessary information. Based on this, new data structures will be developed to better integrate data model information into the digital construction process of railway projects.

Acknowledgements

This research was funded by the Sichuan Provincial Natural Science Foundation (2023NSFC0389); Yunnan Province Major Science and Technology Special Plan Project (202302AD080009); and Yunnan Provincial Science and Technology Plan Project (202305AF150138).

Author contributions

Conceptualization, Y.Y. and J.L.; methodology, Z.Z. and Y.L.; formal analysis, J.L.; investigation, Z.Z. and Y.L.; resources, Y.Y. and Z.Z.; data curation, Y.Y. and J.L.; writing—original draft preparation, J.L.; writing—review and editing, Y.Y. and J.L.; visualization, J.L.; supervision, Y.Y.; project administration, Y.Y.; funding acquisition, Y.Y. All authors have read and agreed to the published version of the manuscript.

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

These authors contributed equally: Yongyi Yang and Jinsheng Li.
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