The wave of information technology is sweeping across the globe. In architecture, various 3D digital design software are playing an increasingly important role in the creative processes of architects, helping them expand their imagination and transform virtual concepts into reality. Many avant-garde architects, both domestic and international, have successfully integrated software with human creativity to produce unprecedented architectural visuals and spatial experiences. However, traditional social concepts, industry systems, design methods, and construction techniques still limit architects’ exploration, especially when designing and constructing large-scale buildings.
With the support of the Shanghai Autodesk China Research Institute, Autodesk Revit 2010 beta software was successfully applied to the construction drawing design of the Mogao Grottoes of Dunhuang Tourist Center, offering a novel experience for architects. The insights and lessons gained during this project are valuable and worth sharing.
Situated on the edge of the Gobi Desert and facing the vast expanse of sand, the Mogao Grottoes Tourist Center emerges from the earth like a gust of wind shaping the dunes—flowing up and down, free and uninhibited. Multiple free-form roofs intertwine, twist, and separate, some perforated with openings that cascade down like an hourglass. The main indoor public space reveals curved cross-shaped beams resembling the coffered grids found in caves. The facade windows draw inspiration from the cave openings carved into cliff walls, featuring arc-shaped chamfered niches on the double-layered walls. These complex forms give the buildings a unique appearance but also present significant challenges for construction drawing design.
Considering cost constraints and local construction capabilities, cast-in-place reinforced concrete was chosen over steel structures for the main framework. This made the precise positioning of three-dimensional curved concrete forms a critical challenge. Questions such as how to model, locate, section, and detail these elements, and how to provide practical guidance for future construction, diluted the creative excitement during the design phase and had to be addressed one by one.
3D Modeling
3D modeling was the most critical task in the construction drawing design. We aimed to use Revit to accurately represent the three-dimensional shapes and spaces and convert them into two-dimensional drawings for precise positioning. Leveraging BIM’s advantages, this approach was intended to improve efficiency, facilitate modifications, and reduce workload.
Our workflow began by breaking down complex tasks into manageable work packages based on a unified logical structure. This pyramid-like tree structure further decomposed medium-difficulty tasks into many simple, standardized actions to ensure quality and consistency. Work results were then combined in reverse order to produce the final solution.
Specifically, the process included these steps:
- Using a 2m × 2m grid axis, aligned with typical concrete formwork dimensions, as the basic positioning scale for the building’s plan and space; all positioning was linked to this grid.
- Separating the vertical walls from the curved roofs, assigning two team members to work on each part.
- Further decomposing the curved roofs according to set rules, modeling each element individually, and then reassembling them to complete the overall model.
Curved Roofs and Three-Dimensional Curved Beams
We began by decomposing the model: the longer roof was split into two zones—east and west—based on structural deformation joints. These zones were further broken down into individual curved roofs based on shape variations. Finally, each curved roof was disassembled into basic structural components such as main beams, secondary beams, slabs, parapet walls, and overhead roof panels. This method allowed us to break down the complex surface model into fundamental units.
Each basic component was then defined and numbered within its zone. This numbering system, built on the axis’s logical foundation, ensured the uniqueness and spatial certainty of every element. We compiled a detailed table listing each component, including the person responsible, completion status, location, and difficulty level. Each modeler received a partitioned combination map—a kind of roadmap showing how the complex modeling task was divided, workload distribution, module integration, progress status, missing parts, encountered issues, and estimated completion times.
This approach also alleviated the initial intimidation of the complex form by focusing on producing individual elements with varying difficulty levels. If a particularly complex unit couldn’t be further broken down—such as cross beams and funnels—we collaborated with the Autodesk technical department or even leveraged resources from Autodesk’s US headquarters. This task division also facilitated outsourcing when necessary.
Next, we created the basic components based on the partition map. Due to time constraints, after brief training sessions with Autodesk technicians, our team learned while working. The steps included:
- Cutting and depicting cross-sections based on the schematic model.
- Producing component surfaces individually according to their assigned numbers.
- Importing surfaces into the project environment and positioning them using the unified coordinate grid.
- Assigning properties such as beams, slabs, and columns, and linking walls to roofs.
Most of our time was spent repeating these steps. Since the building form was highly irregular and components rarely repeated, the workload was heavy. We encountered many challenges during modeling, especially with three complex elements: the cross-shaped beam on the reception hall roof and courtyard, the “funnel” structures, and the spatial curved beams.
For the cross-shaped beams, significant effort went into resolving torn surfaces, maintaining curvature consistency at connection points, applying UV lines for grid adjustments, and creating family files for use on surfaces. Producing the funnels was similarly labor-intensive, requiring repeated trials to decompose, create surfaces with varying curvatures, assign modular family files, and connect them smoothly.
Spatial curved beams were somewhat easier to produce since they were based on the curved roofs. We extracted roof components where the beam top elevation matched the roof top. The beam’s centerline was located on the plane, with column midpoints as endpoints (for beams embedded in columns). Beam projections were determined spatially, and continuous points were connected on the roof’s spatial plane to form polylines. Using structural height, the beam’s actual height was replicated along the z-axis, and the wireframe enclosed by the two polylines formed the beam’s center section. This was imported into the Revit model and assigned thickness, generating the spatial curved beams.
Walls, stairs, and windows posed fewer challenges as Revit handles regular geometries well and offers a rich library of conventional components. Vertical walls can be adjusted in height and thickness via parameters and include extension and chamfering functions. Stair parameters are detailed, allowing quick construction of steps, railings, and handrails. The only difficulty was creating niches and windows with curved chamfers inspired by caves, which required custom family files. Once created, these files could be inserted into walls at various positions and heights, with sizes and proportions adjustable through parameters, greatly simplifying the process.
Positioning
Revit alone could not fully resolve the spatial positioning of curved roof panels, beams, and arbitrary cross-sections. To address this, we used Rhino in combination with Grasshopper scripts for the final spatial positioning. The key was the Grasshopper scripts, which varied depending on the structural component type. This required organizing scripts and calculating 3D positions via these scripts to provide accurate drawings for the structural engineers.
The positioning workflow was as follows:
- Extract structural components from Revit and export them as CAD files.
- Import the CAD files into Rhino and calculate spatial positioning heights using pre-arranged Grasshopper scripts.
- Export the results back as CAD files from Rhino, organize them, and submit them to the structural department.
All planar positioning was based on the 2m × 2m grid, extended into a 2m × 2m × 2m spatial grid coordinate system covering the entire building. All structural components—irregular roof panels, curved beams, etc.—were placed within this grid. The coordinates were recorded as (x, y, z), with x and y spaced at 2m intervals. The z-axis height was calculated by Grasshopper in Rhino, completing the positioning process.
The accuracy depended entirely on the grid size: the smaller the grid unit, the higher the precision. For complex shapes, more positioning points facilitate construction and ensure the final result meets design requirements.
Generation of 2D Drawings
Traditional 2D design separates plans, elevations, and sections. Drawing sections often involves rotating and aligning plans, which becomes confusing and error-prone in complex, multi-floor buildings. The most frustrating scenario is when a plan changes late in the process, forcing time-consuming realignment, section modifications, and cascading updates to annotations, texts, and detail drawings.
In Revit, plans, elevations, sections, details, and dimensions are all linked to the 3D model. Any modification updates all associated drawings automatically, saving time, greatly improving efficiency, and eliminating the risk of missing updates. In this project, with the curved roofs’ diverse variations and unpredictable section locations, this real-time associative functionality proved invaluable. We only needed to set up the associations once and could confidently modify the model.
Unfortunately, due to differing properties of components like roof panels and walls, Revit struggled to chamfer and intersect them correctly, so the resulting profiles did not meet our drawing standards. Additionally, the software’s localization did not align with our traditional expression habits. Ultimately, we had to revert to CAD to reorganize and output the drawings.
Advantages and Disadvantages of Revit Software
Revit offers powerful functionality, an intuitive interface, and supports collaborative design. It provides a platform for various disciplines to collaborate in 3D on the same software, which holds great promise. However, due to significant differences between design requirements and the Chinese market, currently only architects use it extensively, while other disciplines must abandon it because some basic needs remain unmet.
BIM is the fundamental purpose behind Autodesk’s creation of Revit—a revolution compared to 2D design. It aims to consolidate all building-related information into a single document, covering architecture, structure, plumbing, heating, and electrical systems. This model can be modified and updated throughout the design, construction, and future operation phases, keeping information current and integrated.
This integration eliminates the traditional separation between blueprints and negotiation documents. Renovations can directly reference the latest drawings, avoiding time-consuming rechecks of outdated plans riddled with errors and negotiation sheets. This is a major advantage for all stakeholders.
However, to fully realize this, BIM models must contain comprehensive information, requiring all disciplines to express their content within the model and modify it consistently during construction negotiations.
For construction drawing design, the association between 3D models and all plans, elevations, and sections prevents the common errors of missing updates, greatly enhancing drawing efficiency. Revit excels in curve modeling and can generate complex shapes through methodical exploration, though surface modeling still needs improvement. Its parametric design capabilities allow easy dimension changes and local control via family files, performing well for buildings with simpler shapes.
In this project, a fundamental issue was translating the 3D model into 2D drawings that meet the localization requirements of the Chinese construction market. The software must adapt to national standards (calculation, drawing) across disciplines and align with engineers’ traditional drafting habits. These drafting standards have been widely used for years by engineers and construction teams.
As an external version of Revit, many features require redevelopment to suit China’s context. We strongly recommend that the Autodesk China Research Institute devote significant effort to addressing this issue in the next development phase.
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