OpenBIM Facilitation for DfMA in Murray Road HK

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The documents reflect the current best practice and do not claim to be complete. They should not to be understood in the sense of a generally valid recommendation or guideline from a legal point of view. The documents are intended to support appointing and appointed parties in the application of the BIM method. The documents must be adapted to the specific project requirements in each case. The examples listed do not claim to be complete. Its information is based on findings from practical experience and is accordingly to be understood as best practice and not universally applicable. Since we are in a phase in which definitions are only emerging, the publisher cannot guarantee the correctness of individual contents.

This use case illustrates how the practice of openBIM can facilitate the DfMA (Design for Manufacture and Assembly) process in non-typical free-form architectural design. The fabrication of a facade curb is used as an example to highlight the main challenge faced by general contractors: balancing sculpting according to design intent and optimizing the manufacturing process. To achieve this goal, the adoption of openBIM practices becomes indispensable, as it ensures solid data exchange requirements and provides a clear process map, thereby facilitating a smooth data flow throughout the product life cycle. Furthermore, it enables different parties to utilize their professional software without sacrificing tool interoperability.

Project Description

Upholding the vision of an "Icon Amongst Icons," The Henderson Tower aims to create an urban oasis in the central business district. The project's objectives include sculpting and materializing an unprecedented architectural design, optimizing functional space and skyline views, and providing an internationally qualified green and high-performance building for occupants and the neighborhood. These objectives are driven by innovative technologies, engineering excellence, and openBIM software, and are practically implemented by a project team with a wealth of knowledge in openBIM and information management.

Problem Statement

The Henderson project features more than 60% cylindrical or double-curved glass panels, along with the assembly of 16,000 tons of prefabricated steel. Craftsmanship and precision are highly emphasized for such a vast amount of prefabrication. This necessitates early involvement of a broad range of specialties for coordination. By immersing themselves in an openBIM project environment, different project parties can coordinate without relying on a particular software solution. OpenBIM ultimately ensures high data integrity for information exchange, cost effectiveness, and even enables the possibility of DfMA using parametric design approaches.

Full Life-Cycle OpenBIM Information Management

The solution to addressing all technical challenges requires early involvement from a wide array of project parties, each highly specialized in their respective trade and equipped with their own tools. With the participation of over 20 OpenBIM parties and 15 proprietary BIM software, it is crucial to ensure data interoperability during coordination among such diverse specialties, while still maintaining the native data framework and solutions of each specialty. This can only be achieved through information management using the openBIM approach.

Furthermore, extensive training on openBIM-compatible tools (such as Trimble Connect and Solibri) has been provided to site engineers and staff, enabling them to harness the advantages of openBIM for their day-to-day tasks. Given the positive feedback and increase in productivity, we believe that enhancing openBIM awareness and capabilities of practitioners would be beneficial to both the project and the industry.

The openBIM software-neutral platform is also employed for MEP (Mechanical, Electrical, and Plumbing) coordination and subsequent associated BIM applications. The base model is created in Revit, the steel model in Tekla, the façade models in Rhino, and the interior fit-out models in Digital Project and CATIA. These models are exported to the IFC format for regular coordination. This is particularly important in this project due to the non-standard floor layout and vertical routing configuration.

Generative Design

Featuring a free-form architectural design, this project incorporates a wide variety of facade glass panels. Generative design is employed to rationalize the diversity in facade geometry, ensuring efficient manufacturing while preserving the architectural form. The design model, created in Digital Project and CATIA, was exported to Rhino for analysis using Grasshopper. The analyzed models were then exported via IFC for coordination purposes and via STP for fabrication. OpenBIM facilitated the entire process by offering a software-neutral platform for information exchange, ensuring data integrity that is adequate for the fabrication stage.

Integrity of Geometry

The project's free-form geometry serves as both a highlight and a challenge. Due to the stability and robustness of the IFC2x3 format, it was initially chosen as the preferred option for IFC data exchange in our project. The free-form geometry model created in Rhino was exported to the IFC format using a third-party add-in, as Rhino does not have a direct export option. However, zig-zag edges were observed in the free-form geometry when using IFC 2x3. It is suspected that the geometry was triangulated. Considering the ultimate goal of fabrication and detailed analysis, such distortion is undesirable. Therefore, the STEP format, specifically designed for manufacturing, was adopted instead of IFC2x3 by the fabrication supplier. Although the STEP format maintains geometry integrity, the consistency of the model exchange format is affected since IFC2x3 is used for data exchange with other trade models.

Further examination of the IFC-4 Add 2 (4.0.2.0) protocol revealed that free-form geometry can be expressed using NURBS surfaces, which offer greater accuracy and hold promise for fabrication-related purposes. In the future, it would be valuable to conduct preliminary studies and trials on exported free-form geometry using different formats. It would also be beneficial if practitioners could share their experiences regarding the fabrication performance of free-form models exported in formats such as IFC-4, STEP, or IGES. Moreover, the geometry integrity could potentially be enhanced if software like Rhino provided a direct IFC export option.