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Computer-aided Interpretation

of Drawings for Rebar Cage Assembly

How might we improve the process of interpreting drawings for assembling rebar cage and improve the accuracy of the assembly?

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Challenge Statement Owner
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Hear directly from the challenge statement owners!

Review the presentation video and slides from the Q&A session.

01 Intepretation by skilled personnel
01 Intepretation by skilled personnel 1.
02 Identify, collect and sorting of mate
03 Preparing jig for assembly
04 Assembly of rebar cages 5
04 Assembly of rebar cages 4
04 Assembly of rebar cages 3
04 Assembly of rebar cages
04 Assembly of rebar cages 2
04 Assembly of rebar cages 1

Background and Current Practice

Constructed modules for Prefabricated Prefinished Volumetric Construction (PPVC) need to be reinforced with metal meshes and reinforcing bars (also known as “rebars”). The figure below depicts an overview of the process to assemble the rebar cages before installing it into the mould:

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Process to assemble rebar cages [Click image to enlarge]

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For this challenge statement, we are focusing on Step 1 of the process to assemble a rebar cage (interpretation of drawings by skilled personnel). The drawings of the rebar cages are different for PPVC modules in every project. From the drawing, the skilled personnel deciphers the type and quantity of rebar parts needed for the floor slab and wall rebar cages, and plans how these parts are to be assembled together. You may find in the Resource section examples of the drawings to be interpreted and a schedule of the 95 rebar parts. The skilled personnel then communicates the assembly instructions to the workers.


Currently, drawings have been successfully converted to 3D models, and this has reduced the time needed to interpret drawings. However, paper-based drawings are still more practical for the workers on the manufacturing floor. 

As the interpretation of the rebar cages drawings is done manually, it leaves room for misinterpretation of the drawings that could result in missing rebar parts. If the rebar cages fail the quality checks, the workers would need to amend and rework those cages with errors.

Examples of rebar drawings [Click image to enlarge]

Rebar Cage Assembly Process - Explained

Opportunities and Key Challenges

The interpretation process could be assisted by the proposed solution to analyse the drawings and/or 3D models, and to provide step-by-step guidance to any workers to determine the required rebar parts and handle the assembly. The solution should be software-based and should support workers by helping them to understand the correct position and assembly sequence for each rebar part.

The solution would be highly valuable in the following situations:


  • When a new module design is introduced in new projects; 

  • When a team of workers are reassigned to accelerate the production of modules that they are not familiar with; or

  • When newly-hired workers are being trained for rebar cage assembly. 

The solution must be able to be used on-site and with portable devices.

Expected Outcomes


The solution reduces the time taken to interpret the rebar drawings, while improving the accuracy of the interpretation, especially during the initial introduction of the drawings.