Customizing Revit for the Precast Concrete Industry
Customizing Autodesk® Revit® Structure can mean many different things based upon user experience and application. To newer users, customizing Revit Structure may simply mean editing out-of-the-box templates, parameters, and families, while experienced users may want to create advanced families with custom parameter sets to achieve their end goal.
As with anything in the Building Information Modeling (BIM) world, the extent of customization must be looked at from a budgetary standpoint. Will the time taken to customize the project and its components boost the overall productivity of the project team? Can the desired results be achieved without spending hours creating a new family component? Can the customization be used to save time on future projects?
In an attempt to answer these questions, this article provides customization tips and tricks while outlining the process of creating fabrication-level shop drawings for the precast concrete industry.
Customization Basics
For even the new user, customization begins with one thing in mind: the end product. For most of us, that means construction documents. What do we want our documents to look like? Titleblocks, annotations, lineweights, and graphics in general convey the company brand. All of these need to be addressed in order for your company to present itself in a professional manner. These typical items can simply be modified from out-of-the-box components, but most companies want their product to stand out from the crowd. This often means creating building project templates, titleblocks with company logos, creating annotation libraries, and utilizing different fonts.
Inside these components is what drives Revit: parameters. Without parameters, Revit would just be 3D CAD. Project parameters, shared parameters, and global parameters can be used to track changes, report information in schedules and annotations, and drive component geometry. Needs for specific parameters will vary from project to project, but it is important to maintain a simple shared parameter file with standard naming conventions.
The process of creating a precast concrete fabrication level of detail model and associated shop drawings demands customization of all items stated above.
Precast Concrete Shop Drawings
Creating precast concrete shop drawings (production-level design documents) is a complex and difficult task. When most people think of precast concrete, they envision simple parking structures with repetitive pieces. This is very rarely the case. Architects and engineers continue to push the boundaries of precast concrete’s capabilities. The amount of detail required for even a “simple” structure can be eye opening to the novice.
Precast concrete shop drawings consist of two main components: erection drawings and piece details. Erection drawings are the overall plans, elevations, connection sections, and architectural details that depict the overall structure. See Figure 1 for a typical wall elevation within the erection drawing package. Piece details contain the detailed information required to build each unique piece of precast concrete on the project. All piece geometry, rebar, reveals, embedded connection hardware, inserts, notches, etc. must be accurately dimensioned on the piece detail. See Figure 2 for a sample wall panel piece detail. Piece details must also include material takeoffs and a bill of materials. Creating erection drawings and piece details efficiently requires significant customization of out-of-the-box Revit.
Figure 1: Precast elevation
Figure 2: Piece detail
Erection Drawings
Most precast concrete detailing projects begin by modeling the supporting structure. The supporting structure can be limited to just foundation elements, or it may also include a structural frame. Figure 3 highlights the foundation and structural steel elements supporting precast wall panels for a small entrance vestibule to a warehouse. The precast concrete components are modeled “on top” of the supporting structure. It is best to model the supporting structure in a separate Revit file from the precast concrete components. The erection drawing model contains the precast components and associated plans, elevations, and details. The supporting structure model most likely will not need complex customization and can be created from typical beam, column, and wall families. The supporting structure is linked into the erection drawing model.
Figure 3: Supporting structure
For certain projects, the design team may provide a Revit file that already has the supporting structure modeled. In these cases, the model can be directly linked into the precast concrete erection drawing model. The Revit project template for erection drawings should include a placeholder link that is updated for the new supporting structure model, whether it is created in house or comes from the design team. Using a placeholder link in the project template will ensure that all customized view template settings will be maintained for each new project, regardless of who creates the supporting structure model.
Once the supporting structure model is completed, modeling the precast concrete components can begin. When modeling precast components, an eye on the end goal must be kept in mind. Components must be created such that information required downstream in the production process can be extracted from the model. When creating insulated sandwich wall panels, the wall must be modeled such that each wythe of concrete and the insulation layer can be accurately quantified. When blockouts are added to create window openings or reveals, the quantity of each material must be updated appropriately.
Out-of-the-box Revit precast families do not provide much help in creating project-specific geometry. Each precast concrete fabricator uses unique formwork to create structural components. The cross section of a double tee or inverted tee beam from Precaster A will not match Precaster B. Family geometry of these types of members must be customized for each precast fabricator. Precast piece families can range anywhere from very simple to very complex to include many variables for varying geometric conditions.
Specific project conditions may dictate how families are created. For a typical parking garage, it is most efficient to create a double tee family that contains parameters for geometric changes such as dapped ends and top flange recesses. Adding these types of parameters into the double tee family will eliminate the need to model numerous voids within the erection drawing model. See Figure 4 for a double tee family with a sample of associated parameters.
Figure 4: Double tee
Shared parameters must be added into the families to report certain identity data. A control number (the unique number for each piece of precast on a project) and the piece mark number (used to denote pieces that are identical) must be included in each family. Other parameters can be added so that production related schedules are automatically populated. See Figure 5 for a sample schedule that is used within the erection drawings. Adding volume and weight to the schedule allows for all parties involved in the project to see information about the pieces as they are created and modified throughout the design process. The weight of each piece is essential for the precast erector to select the correct crane to safely place precast components at the construction site.
Figure 5: Piece schedule
Precast to precast and precast to supporting structure connections must also be modeled to be included on the erection drawings. Each connection is created as a nested family composed of individual hardware families. Individual hardware is typically created as a face-based generic model family and the overall nested connection family is a face-based structural connection family. Nested families work very well when small changes to the connections are made or when connection locations are adjusted. If any part of the connection has to cut a piece of precast, the “Cut with Voids When Loaded” button within the connection family must be selected.
For nested families to work properly, the individual hardware components must have the “shared” button checked within its own family (see Figure 6). Selecting the shared button allows the individual hardware components of the nested connection family to be selected and scheduled independently. Figure 7 highlights a single piece of hardware utilized in a wall panel tie-back connection.
Figure 6: Shared button
Figure 7: Connection family
Shared parameters for specific hardware can include the finish (galvanized, primer, etc.) and whether the hardware component is needed in the precast plant, at the construction site, or at the steel fabrication shop. Hardware components should be centered on the reference face within the family. Reference lines are added where needed to provide a reference for dimension lines once the family has been added into the project. Orientating individual hardware elements in relation to each other is achieved within the nested connection family.
Piece Details
Piece detail creation occurs after the erection drawings have been submitted and approved by the architect and structural engineer of record. Revit assemblies are used to create each piece detail. Assembly views for each piece are created using customized view templates. View templates vary for each type of precast component (walls, beams, columns, etc.) and for each type of view (casting plan, reinforcing plan, sections, etc.).
When the piece detail process is started, each precast component is complete and already accounts for all piece geometry and connection placement. As such, the focus of creating the piece detail becomes adding dimensions, tags, schedules, and material takeoffs to complete a finished fabrication drawing.
Numerous items must be scheduled to complete a piece detail. See Figure 8 for an example of items which are included within the piece detail titleblock. Unfortunately, Revit is limited when it comes to automatically adding assembly data directly into title blocks. Volumes and weights for each piece detail are created using a material takeoff. The bill of materials is created using schedules for each type of component. As an example, hardware and rebar must be scheduled separately because they are created as generic models and structural rebar, respectively.
Figure 8: Titleblock
Customization Process
Whether you are still transitioning from AutoCAD® to Revit, working for a new client, or just updating your own Revit standards, customization is a very important part of daily Revit use. As projects are completed and lessons learned, new thinking may lead to a realization that customizing Revit in a different way can create increased efficiencies. Taking the time to change standards or typical workflows is more often than not worth the initial investment. Not only are you working toward a more efficient way of doing things, but you may also learn something along the way that can help in another area.
Much of the customization process is trial and error. There are limitations to all software packages, which can make obtaining the desired results difficult. It is impossible to predict when these limitations will be discovered or how to work around the issue. The saying, “you don’t know what you don’t know” certainly applies.
Understanding that time is the most important part of the customization process is vitally important. Lessons learned are meaningless if nothing is changed as a result. Time must be allocated for customizing as necessary to increase efficiencies and take advantage of features in newer versions of Revit.
Customizing Revit Structure is absolutely necessary to survive in the ever-changing Architecture, Engineering and Construction industry. There will be complications along the way, but you should not be afraid to struggle. The hard, sometimes frustrating work of customizing Revit will be a benefit to you, your colleagues, and your firm.
Michael Hopple, P.E. directs the Virtual Design Solutions (VDS) department at Providence Engineering Corporation, a consulting structural engineering firm in Lancaster, Pennsylvania. The VDS group provides Building Information Modeling services across the Architectural, Engineering and Construction industry. Michael can be reached for comments and questions at mikeh@proveng.com.
Zachary Engle is a structural and architectural Revit designer with CORE Design Group in York, Pennsylvania. CORE Design Group provides architectural and engineering services for the commercial and residential building industries. Zachary can be reached at ZEngle@CORE-DesignGroup.com.
