In order to achieve digital delivery of design results, the following key technical issues need to be considered: delivery of design results based on metadata, adaptive transformation of traditional design systems, approval process of digital delivery, and data security protection.
2.1 Metadata based design deliverables
2.1.1 Metadata Creation and Management
Digital delivery requires the data of different participants at different stages to flow between different links, but the data format output by different participants is likely to be inconsistent. Therefore, it is necessary to standardize the delivery process and deliverables of all stages and participants, so that they can carry out digital delivery of design results according to unified data standards and delivery formats. In order to solve this problem, since 2019, the Railway BIM Alliance has started the research on the delivery of electronic documents of design results in a unified format, established the creation and submission method of design results data based on metadata, and proposed the document organization method with design units as divisions. Taking the railway signal discipline as an example, based on the unified railway metadata compilation template (Excel format), the compilation of metadata has been completed. The compilation content includes project type, personnel type, document type, organization type, engineering quantity and other information, and the key business metadata has been sorted out from the following aspects: basic information, data type, data constraints, value range, data relevance Data additional information. See Table 1 for an example of railway signal metadata.
Table 1 Example of railway signal metadata
The next step is to perform data verification on the metadata Excel file. This process is usually completed automatically by the software. The purpose is to check whether the content, format, structure and value range of each metadata conform to the rules. Once verified, metadata can be converted to text-based structured exchange format, such as json or XML. Considering that json has the advantages of being lighter and simpler, the railway adopts json format more often. For example, the json Schema corresponding to the metadata of train control level of railway signal system is shown in Figure 2.
Figure 2 json expression of train control system level
It should be noted that for the above process, the metadata Excel file can also be converted to json or XML format before automatic verification. The specific method is subject to the situation, and both methods are feasible.
The transformed json or XML file is also called Schema data form. Schema has a strong structure, clearly defines the structure, format, constraint, value range, association relationship and other information of the delivered content, and can be directly recognized by the computer. The metadata schema can not only verify the design result data, but also directly generate the design result data model and data entry interface. The design result data can be created through the data model generated by the metadata schema.
2.1.2 Metadata based delivery method
As the main medium and carrier for the delivery of design results, the metadata schema facilitates the data exchange of various disciplines. The design result delivery process based on metadata schema is shown in Figure 3.
Step1 Create professional metadata and export it to a Schema file, export a set of data form Schema files and a Schema file after the delivery file structure tree;
Step2 Instantiate the two Schema files to generate the data filling interface and the delivery file structure tree. The delivery document structure tree is a structured document delivery template, which defines the basic information such as project name, design stage, professional name, and the name of each design unit of each discipline. Each node of the file structure tree contains information such as the delivery file name, file path, file type, and historical version;
Step3 Document hooking and data filling shall be carried out according to the Measures for Preparation of Pre feasibility Study, Feasibility Study and Design Documents of Railway Construction Projects (GTKF [2018] No. 93);
Step4 Conduct data verification, and generate the delivery file compression package and file directory after passing the verification, which will be handed over as a whole as the deliverables of this stage.
Figure 3 Design result delivery process based on metadata schema
2.2 Adaptability modification of design system
At present, Schema is the best digital delivery carrier of design achievements. In order to realize the structured delivery of design results based on Schema, the traditional design system needs to be adapted. Specifically, the metadata module needs to be built in on the basis of the existing traditional design system to realize the receipt, verification, management and maintenance of metadata, and support the automatic generation of json/XML Schema data files. The system shall adopt the metadata version officially released by the Railway BIM Alliance, and support regular synchronous update with the latest metadata version released by the Railway BIM Alliance.
2.3 Digital approval
After digital delivery
The review, distribution, archiving and other processes of design results will be changed to online, and the approval process will also be fundamentally changed. In the traditional delivery process, the responsibility identification mainly depends on the signatures and seals of all levels of review. However, digital delivery will make the verification and accreditation more convenient, such as the verification and accreditation of various deliverables by digital means such as electronic signature and electronic seal. In addition, the way of drawing review will also change fundamentally from the traditional paper blueprint review to electronic drawing review. Before drawing review, designers need to upload the electronic documents of construction drawings and BIM models to the digital drawing review cloud platform. In the process of drawing review, reviewers can annotate and reply online to the electronic documents of construction drawings and BIM models. The reviewed comments and opinions will be stored in the digital drawing review system, and all participants can view the drawing review and modification in real time on the platform, so that all participants can communicate and exchange on the same platform, realizing online approval supervision and transparent design delivery.
2.4 Data security protection
In order to ensure the security of data in the process of digital delivery, the upload, review and circulation of deliverables should be carried out in a private network environment isolated from the Internet. At the same time, active security defense mechanisms such as identity authentication, authority control, data encryption and data backup should be adopted, supplemented by security vulnerability scanning and network attack and defense testing, Guarantee and improve the data security of the digital delivery platform from multiple dimensions to ensure that the data will not be lost, disclosed, accessed or tampered with maliciously during the transmission process.
Three digital delivery implementation path
The implementation of digital delivery should first define the delivery requirements, delivery contents and delivery processes, and based on metadata, organize the delivery contents of various disciplines in a structured way. At the same time, make adaptive transformation on the traditional design system, and then complete the digital delivery of achievements in all stages of the whole life cycle on a unified digital delivery platform.
3.1 Division of design units
The document organization structure of railway digital delivery is generally based on the hierarchical mode of "project name - line (line type) - discipline - design unit". The design unit is a relatively independent and complete engineering unit within the discipline, such as the interlocking system of a station and the block system of an interval []. The digital delivery of each discipline is divided by design unit, and the division basis and method of design unit of each discipline may be different. Taking the railway signal discipline as an example, the division of design units is mainly based on the Measures for Preparation of Pre feasibility Study, Feasibility Study and Design Documents of Railway Construction Projects (GTKF [2018] No. 93) issued by the State Railway Administration, and the Measures for Delivery Management of Electronic Documents of Construction Drawings of Railway Construction Projects (TJS [2020] No. 123) issued by the State Railway Group And a series of standards issued by the Railway BIM Alliance. According to the above methods and standards, in combination with the specific situation of the railway signal discipline, the railway signal design unit is mainly divided by subsystems, including: train dispatching command and centralized dispatching, train operation control, section blocking, interlocking, hump signal and marshalling station automation, signal centralized monitoring, turnout snow melting, and other signals, as shown in Figure 4. The lower level of the above design units can be divided into the dispatching center of the railway bureau, the monitoring center of the signaling depot, the station, the relay station, the yard/depot/station, the line and section signal engineering, the track maintenance or comprehensive maintenance organization, etc. according to the specific work points, as shown in Figure 5. In addition, when the same design unit belongs to different budget sections, it should be further split.
Figure 4 Division of Railway Signal Design Unit
Figure 5 Division of next level work points of railway signal design unit
3.2 Delivery content and format
iron Delivery of road signal design results The content includes a full set of documents related to the design, as well as the description of the drawing content and the electronic version of the drawing supply list. As shown in Figure 6, railway signaling mainly includes four types of deliverables: Descriptions, attachments, figures and models. Among them, "description" files are mostly document files, "attachment" files include form files and document files, "attached drawings" are two-dimensional design drawings of each design unit, and "attached models" are three-dimensional BIM models and model descriptions of each design unit. The delivery content of "instructions, attachments, and drawings" is consistent with the traditional delivery, while "attachment" is the new delivery content in the digital delivery, mainly including the three-dimensional layout model of indoor and outdoor equipment (including cable laying). At present, the delivery of drawings of railway signal discipline is mainly two-dimensional, giving consideration to BIM delivery, and gradually transitioning to BIM delivery. It should be noted that not all drawings of railway signal discipline are suitable for three-dimensional delivery (such as circuit diagram, interlocking table, system diagram, etc.). Even in the future BIM dominated delivery of such drawings, two-dimensional delivery is still recommended.
Figure 6 Deliverables of Railway Signal Design Results
The design deliverables shown in Figure 6 can be classified into structured data files and unstructured data files. Among them, structured data files refer to data that can be logically expressed and realized with a two-dimensional table structure, including the structured parts of the specification and various schedules. Unstructured data files include drawings, documents, BIM models, etc. The structured data exchange format (such as json or XML) based on text is adopted for the delivery of the main data that can be structured, such as the specification (the part that can be structured), the bill of quantities, the quantity of equipment and main materials, the list of materials and equipment supplied by Party A, the list of standard drawings and general drawings, etc Constraints and other requirements shall be implemented by referring to the metadata design and delivery form Schema published by the Railway BIM Alliance.
As shown in Figure 7, all kinds of unstructured data (attachments, drawings, and templates) associated with the delivery subject Schema are delivered in the following formats: ① drawings and documents are delivered in PDF format in principle; ② In principle, BIM models can be delivered in IFC format or in third-party lightweight format; ③ Other forms not required to be structured can be delivered in Excel format.
Figure 7 Delivery format of railway signal design achievements
3.3 Delivery process
Digital delivery mainly includes design delivery of "design construction" and completion delivery of "construction operation and maintenance". Among them, design delivery is divided into four stages of "pre feasibility study, feasibility study, preliminary design and construction drawings", and the main body of delivery is Schema documents and various attachments, drawings and models associated with Schema documents. The delivery process is as shown in Figure 8. The construction unit is responsible for formulating the implementation rules of digital delivery management. The survey and design unit completes a full set of electronic documents of design achievements at each stage according to the requirements of the construction unit. After passing the review, the design achievements are submitted to the digital delivery platform. After receiving the electronic documents, the platform management unit issues a receipt confirmation with an electronic seal. The receipt confirmation form shall be in triplicate, which shall be kept by the digital delivery platform management unit, the survey and design unit and the construction unit for future reference; Then the construction unit shall organize construction drawing consultation, construction drawing review, document verification, etc. for the design documents submitted by the design unit; The construction unit shall deepen the construction drawings based on the design results. If there is any design change, the change information shall be fed back to the design unit after the change is approved, and the design unit shall change and modify the construction drawing. After the construction is completed, the construction unit will upload the complete set of electronic documents of the completion deliverables to the digital delivery platform. Finally, the construction unit will organize the digital acceptance of the completion delivery data. After the acceptance, the digital assets will be handed over to the operation and maintenance unit for filing. During the whole delivery process, data security protection measures shall be taken as described in "Section 2.4".
Figure 8 Digital delivery process
IV Digital delivery platform
The digital delivery platform is used to carry and manage the delivery information in all stages of the whole life cycle, The platform can integrate with a variety of engineering software and be compatible with a variety of file formats , improve delivery quality and efficiency by integrating data, information, personnel and processes.
4.1 Platform objectives
The digital delivery platform takes the project delivery business as the main line, the whole life cycle information management and sharing as the concept, and the formation of high-quality digital assets at all stages as the goal. It serves the construction unit, the design unit, the construction unit, the operation and maintenance unit and other participants, regulates the behavior and results of digital delivery of all participants, and prevents information attenuation and data fault in the delivery process, Realize information transmission and data sharing throughout the project life cycle. It is mainly manifested in the following two aspects:
1) One time filling and whole process application
After completing the first data filling on the platform, the filled data will be stored in the engineering database, and these data will be transferred and shared during the whole delivery process. The same data information does not need to be filled in again. If any data is modified, the associated data will be updated synchronously. The filled data can be used online throughout the life cycle of the project, so that the data can be transmitted efficiently and losslessly, and the data can be used effectively.
2) One platform, multi-party collaboration
The platform has broken through the existing delivery method. All project participants work together around one platform, implement paperless delivery throughout the process, and effectively strengthen the collaborative sharing of files and efficient use of data. The platform provides open and transparent query management and trace management, truly realizes the online delivery of results and process supervision, plays a positive role in accurately controlling the delivery process, and greatly reduces the delivery workload and enterprise operating costs.
4.2 Platform architecture and functions
The digital delivery platform can be divided into three layers from the perspective of data flow, namely, the data source layer, the digital delivery platform layer and the business application layer. The data source layer provides basic data for the digital delivery platform, including project data such as design, construction, operation and maintenance, and railway basic metadata. The platform layer is divided into data collection layer, data processing layer and data security layer. The data collection layer is responsible for receiving and integrating various data from the data source layer; The data processing layer is the core part of the platform layer, which is responsible for the management, viewing, analysis, proofreading, signing, circulation and other functions of various delivery data; The data security layer provides the platform with security protection functions such as authentication, permission management and data encryption. The business application layer is responsible for realizing various business applications in the process of digital delivery, including the delivery of design results, completion results and digital archiving. The architecture of digital delivery platform is shown in Figure 9.
Figure 9 Overall Architecture of Digital Delivery Platform
4.3 Application
At present, the four electricity BIM technology and application project of the Guiyang Nanning high-speed railway is based on the new Guiyang Nanning high-speed railway and the localization software Railworks to build an integrated delivery platform for the four electricity construction, operation and maintenance, to achieve the digital delivery of three-dimensional models, data and related documents in the whole process of design construction operation and maintenance in the four electricity project, which can effectively ensure the data security of railway information, Reduce data loss during delivery. In the process of project construction, construction changes were reduced about 7 times, 2 million yuan was saved, the construction period was reduced by 20 days, and more than 100 concealed works were damaged. At the same time, the platform can meet the access of the railway operation and maintenance management system, provide accurate spatial location and equipment information in the operation and maintenance management phase, support the operation and maintenance decision-making and maintenance work, and improve the efficiency and reliability of the operation and maintenance management. The four electricity BIM delivery platform of Guiyang Nanning high-speed railway is shown in Figure 10 and Figure 11 below.
Figure 10 Main Interface of Integrated Delivery System Platform for Building and Maintenance of Four Electric BIM of Guiyang Nanning High speed Railway
Figure 11 Online Deliverables of Part of BIM Construction, Maintenance and Delivery System Platform of Guiyang Nanning High speed Railway - First Piece Station Model
This paper analyzes the characteristics of the traditional delivery of railway design achievements, proposes the important means of digital delivery, and focuses on the key technologies in the process of digital delivery. The scheme of realizing digital delivery of design achievements based on metadata schema solves the two major problems of "what to deliver" and "if to deliver" in digital delivery, and provides ideas and methods for future digital delivery schemes of other industries in the railway field. What needs to be further pointed out is that the current railway digital delivery system is not perfect, and the follow-up needs to further strengthen the research on delivery standards, delivery platforms, and delivery processes, and gradually transition to a BIM led delivery mode, making full use of digital advantages to achieve information transmission and data sharing throughout the project life cycle.
