BIM to Fabrication: Revit Structure for Detailed Precast Shop Drawings

Precast concrete modeling involves the digital visualization of prefabricated concrete members using BIM software. This involves creating accurate 3D models of structural connections, components and embedded features. This streamlined process aids in design coordination, clash detection, and fabrication, leading to precise component production, reduced errors, and less on-site rework.

In the construction industry, the increasing demand for shorter project timelines, cost efficiency, and better quality control highlights the importance of precast concrete modeling. Precast construction offers advantages in accuracy and speed, but traditional design and fabrication methods often lead to challenges. These issues stem from disjointed communication, errors in converting 2D drawings into 3D structures, rework and on-site clashes.

Precast concrete modeling provides an accurate, detailed and data-rich representation of the precast structure, enabling seamless collaboration and efficient on-site assembly. Architects and engineers benefit from improved design coordination and visualization, while manufacturers experience streamlined production workflows and reduced material waste. Contractors can use precast concrete modeling to minimize rework and delays and optimize on-site project erection, ensuring smooth project execution.

What is the significance of BIM in precast concrete modeling?

BIM integration in precast concrete modeling promotes seamless data collaboration and exchange throughout the project lifecycle. It facilitates interference detection, improves precast fabrication and allows for precise 4D scheduling and 5D cost estimation, resulting in greater efficiency and reduced errors in precast construction.

How is Revit for construction modeling different from modeling other structural systems?

Unlike specialized structural analysis software, Revit offers multidisciplinary coordination. Its parametric modeling capabilities enable project stakeholders to collaboratively design, analyze and document the entire building within a single BIM framework. This enhances communication and clash detection, leading to improved project outcomes.

The challenge is assigning unique production data to precast elements in Revit. If there are too many variations, such as in length, that create a new type, it can lead to numerous types, making project navigation difficult. If every element is a similar type and production data is instance-based, there is a risk of identical elements having different production data, causing confusion. For example, consider a 10’ wide double tee, which can sometimes be 20’. Should this length difference create a new Revit type? If every double tee is identical, there is a possibility of confusion in tracking data.

Concepts to get started with precast modeling in BIM

Precast modeling in BIM involves representing precast members with accurate geometry, reinforcement connections, and embedded features. It starts by importing architectural and structural 3D models into the BIM environment, followed by generating an accurate and detailed 3D visualization of individual precast components. Parametric families allow for effective and efficient changes and variations to ensure accurate fabrication.

Reinforcement modeling includes precise bar placement, Bar Bending Schedules (BBS), and clash detection. Connection modeling involves modeling various connection types, such as corbels; embed plates, and grouting details. Finally, shop drawings and fabrication data are generated directly from the 3D BIM model to streamline production and reduce errors.

• Concrete volume: Early material planning and cost estimation.

• Piece type and count: Production operations, scheduling, and erection planning.

• Connector plates count: Timely availability of material on-site.

• Custom length/weight parameters: Check maximum dimensions and crane lifting capacities.

• Custom design type: Clarify connections between calculations and shop drawings.

• Piece marking: Track elements from design to erection, aiding scheduling.

• Marking: Differentiate identical pieces with varying erection timelines.

• Flagging: Highlight long lead-time components for procurement.

Image source: mdpi.com

A 3D precast concrete model with 5mm clash coordination for M60 concrete grade saves costs for a residential project in the UAE.

A precast manufacturer from the UAE contacted the team at TrueCADD for a residential project. AutoCAD drawings, PDF and Excel files were provided by the client. Read the complete case study on how the team used Revit, Navisworks, BIM360 and Excel to create a 3D model at LOD 450 with clash coordination under 5mm for M60 concrete grade with rebar shop drawings and Bar Bending Schedules. The final deliverables led to:

• Cost and time savings

• Improvements in production quality

• Faster and more accurate erection due to proper planning and sequencing

  

Building a Family Library of precast members

Walls:

• System families: Utilize Revit’s in-built “Structural Wall” system family for precast panels. Customize properties for materials, thickness and structural parameters.

• Loadable families: For unique panel configurations, create loadable families. Define parameters for dimensions, openings and embedded features.

• Nested families: Utilize nested families to model complex wall details, such as chamfers, reveals and surface patterns.

Columns:

• System families: Begin with the “Structural Column” system family for circular or rectangular columns. Adjust parameters for materials, dimensions and reinforcement.

• Loadable families: Create loadable families for non-standard column shapes (L-shaped tapered) to include connection details like haunches or corbels.

• Shared parameters: Use shared parameters for attributes such as column ID, length and concrete strength to facilitate coordination and scheduling.

Framing members:

• Structural framing families: Use Revit’s “Structural Framing” families (braces, beams) as a benchmark for precast framing. Modify parameters for materials, cross-sectional shapes, and reinforcement.

• Adaptive components: For complex geometries or curved members, consider adaptive components. These allow greater flexibility for project-specific requirements.

• Connection details: Model connection details like end plates, bearing seats, and lifting loops within the family or nested families.

Steel connection plates:

• Generic models: Create steel connection plates as model families. Utilize voids and extrusions to define the plate’s openings and shapes.

• Nested families: For plates with bolt patterns, consider nesting other families within the plate family.

• Material parameters: Assign the appropriate steel material to the plate family and define the thickness and dimensional parameters.

Concrete connections:

• Void-based modeling: Model concrete connections like corbels and dapped ends using void extrusions or sweeps within the host family.

• Visibility parameters: Add visibility parameters to control the display of various connection configurations.

• Symbolic lines: Use symbolic lines to represent reinforcement or connection details that are not modeled in 3D.

Other considerations include family templates, shared parameters, LOD and BIM collaboration.

What are the advantages of using Revit’s parts tools to segment precast walls?

Revit’s Part tools give precise control over precast wall segmentation, allowing for better customization. This leads to optimal panel sizes for efficient production, handling and transport. This reduces material waste and project costs.

Using assemblies to seamlessly create composite precast elements

Assemblies in Revit streamline the modeling of composite precast elements. They group precast components, like beams, slabs, and connections into a single model. This simplifies modifying, placing and scheduling these elements. It ensures seamless coordination between precast elements within the 3D precast model.

Process to use a spreadsheet link to perform calculations outside of Revit

• Create a spreadsheet with calculations: Define and build a spreadsheet with calculations, formulas and input cells.

• Use the “Link Excel” tool in Revit: Navigate to “Add-Ins” and locate the “Link Excel” tool and select the spreadsheet file to link.

• Build a live connection: Map the spreadsheet cells to Revit parameters and define the direction of data flow.

• Dynamic data exchange: Once the link is established, changes made to the linked cells will be updated in realtime within Revit parameters.

Conclusion

Precast concrete modeling with BIM has empowered stakeholders to streamline workflows, reduce errors and optimize resources. While challenges remain in element variations and data management, embracing this technology leads to accelerated, cost-effective and high-quality construction. The future of precast lies in its deeper integration with BIM workflows and tools for continued innovation and efficiency.