Overview
In this lesson, you explore how to create building models that more accurately reflect the construction techniques that will be used for the materials and systems specified. As the use of the BIM models that they create expands beyond design activities, the need to deliver accurate models and improve communication of design intent becomes critical to the success of the entire project team.
You will explore how to model building elements and structural systems to reflect common construction practices. You will use a new tool available in the Autodesk Revit platform—parts—to break multi-layer elements into pieces to improve BIM models for construction planning and estimating use. You will also learn to create 3D details and exploded views to enhance your design communications.
The Evolving Roles of Designers and BIM Modelers
As the applications of BIM models continue to evolve and extend beyond design phase activities to supporting information needs throughout the project lifecycle, the importance of accurately modeling the elements of a building or facility grows and becomes critical to the success of all project participants and model users.
The role of designers and BIM modelers is rapidly expanding. As creators of much of the information in a BIM model, they are expected to accurately modeling the elements of a building in a way that serves their needs, as well as downstream and sometimes unforeseen uses of the model.
Some argue that this evolving role is analogous to master builders, who once guided and were ultimately responsible for all aspects of building projects. But that analogy is not appropriate—given the size of complexity of modern construction projects, no individual can carry that load. A better analogy might be to compare designers in a BIM process to orchestra conductors, who understand and appreciate the unique qualities and needs of each of the players, and focus on keeping them all working harmoniously to create exquisite results.
No individual player or BIM modeler can effectively wear all the hats and embody the skills and expertise present in the full project team. So, finding ways to incorporate the unique strengths and value added by each expert, as well coordinating and synthesizing their efforts into a cohesive workflow is the approach we must take.
For this approach to be successful, it is paramount that the BIM model, which serves as the vehicle for storing, synthesizing, and communication information about the building project, accurately convey design intent.
Guiding Themes
- Model at an appropriate level of detail, relative to the stage or phase of the design process.
At the early conceptual design stage, focus on the big gestures (placement, massing, and orientation) and don’t get lost in the fine details. As the design matures through design development and construction documents, successively add more detail as information about building elements is decided.
- Understand your design goals, and use a targeted, iterative design process.
Don’t get distracted by the seemingly infinite design options available in modern modeling software. Explicitly understand the project team’s design goals and priorities, and use these to guide your design exploration. Use an iterative process—model, design, evaluate, and then refine. Use the constructability, cost, and building performance feedback available through analysis of the model to inform design decisions.
- Model it as it will be built, and accurately convey design intent.
Sloppy shortcuts to make model views look right and hide modeling inaccuracies should be avoided when possible. The building elements and the relationships between them encoded in the building model must be buildable and useable for all downstream users and model clients. And these users are depending on the accuracy of the model.
Learning Objectives
After completing this lesson, you will be able to:
- Appreciate the importance of modeling building elements in a manner that matches the planned construction materials and methods.
- Understand and use specific model techniques available in the Autodesk Revit platform to accurately model the spans, boundaries, and layers of building elements for construction.
- Use 3D views, tags, and keynotes to improve communication of design intent and ensure consistency.
Tutorials
Modeling to Match Construction Methods
In this exercise, you will learn how to:
- Use design options to model alternative construction methods.
- Accurately model building elements to reflect planned construction materials and methods.
- Specify element spans, top and bottom constraints, and boundaries.
- Split and subdivide elements to match construction tasks.
- Use Revit extensions to auto-generate models of structural features.
Figure 7.1.1. Modeling structural elements for steel frame construction
- Create design options for modeling two common construction alternatives—cast-in-place concrete and structural steel— for the building in the exercise dataset.
- Use one design option to model the structural frame for the building using concrete structural elements. Assume that:
- All elements will be formed and cast-in-place.
- The planned construction sequence is to build one floor level (including the structural columns and floor slab above) at a time, then move on and repeat these steps at the next level.
- Use another design option to model the structural frame for the same building using structural steel elements. Assume that:
- All steel framing elements will be delivered independently and erected in the field.
- Columns will be joined at 3 feet above each floor level.
- Create a sheet and place similar 3D views showing the two construction alternatives side-by-side for comparison, as shown in Figure 7.1.2.
- Use the Revit Wood Framing Walls extensions to add structural framing elements (studs, plates, and headers) to the exterior wall on the north side of the building.
Figure 7.1.2. Sheet showing 3D views of structural framing options
Using Parts to Improve Model Accuracy
In this exercise, you will learn how to:
- Explore the structure of multi-layer building elements.
- Create parts to separate multi-layer elements into individual pieces for construction modeling.
- Divide parts to model material changes in specific areas.
- Schedule parts for more accurate material and quantity takeoffs.
Figure 7.1.3. Creating parts to separate the layers of a building element
- Create schedules summarizing the areas and quantities of the materials contained in the wall and floor elements of the building in the exercise dataset.
- Create parts to separate the layers of the wall and floor elements, and then divide the parts to more accurately model design features, as shown in Figure 7.1.4:
- Create a checkerboard pattern using two alternative stone materials on the top layer of the floor in the first floor lobby area.
- Adjust the parts of the interior walls in the lobby area to model a special wainscot material to be applied to the lower half of walls on the lobby side.
- Create a schedule of the parts and a materials takeoff to summarize the quantities of the materials in the updated lobby design.
- Compare these quantities to the original estimates from the first step of the exercise.
Figure 7.1.4. 3D view of lobby area with design features modeled by dividing parts
Using 3D Views to Enhance Design Communication
In this exercise, you will learn how to:
- Explore 2D details and callouts in a project.
- Create 3D details to enhance communication of design intent.
- Use parts to create exploded views.
- Add annotations, text, and tags to 3D views.
- Utilize keynotes to ensure consistency.
Figure 7.1.5. Creating a 3D exploded view
- Create a 2D callout showing the details of the lobby interior wall elements from the previous exercise.
- Add annotations, tags, and keynotes to fully explain the features shown in the view.
- Place this 2D view on a sheet.
- Create a 3D exploded view showing the layers of the same wall element.
- Create a 3D view, and then use the Orient to View tool to set a similar viewpoint.
- Adjust the boundaries of the parts to expose the layers of the wall element in the view.
- Add annotations, tags, and keynotes to fully explain the features shown in the view.
- Place this 3D exploded view on a sheet, side-by-side with the 2D view.
- Compare the advantages using 2D versus 3D views for documenting design intent.
Figure 7.1.6. Sheet showing 2D and 3D exploded views side-by-side
Assessment
- What types of building elements are typically affected when refining BIM models to match the building process?
Construction methods can vary greatly due variations in the construction techniques commonly used for different building materials. For example, the sequence of operations and erection strategy is typically very different for steel-frame versus concrete-frame structures.
The elements that are most often in need of refinement include:
- Items that are easily modeled as spanning several floor levels – for example, structural columns and exterior walls. Although these elements will align at each floor level, they will likely be built one or two levels at a time.
- Items that are modeled as multi-layered structures, which are actually building in several discrete steps – for example, floor and roof types that include both structural and finish layers in the type definition.
A good overall guideline is that the elements in the BIM model should broken into pieces that closely reflect the likely construction process.
- What are the essential differences to consider when modeling steel or wood versus concrete building systems?
Steel framing, wood framing, and pre-cast concrete are examples of stick-built systems, composed by placing and assembling lots of individual elements. As these individual elements are modeled, precise placement at the proper height and with the appropriate joining conditions is critical to avoid interferences and create accurate models that will be useful for construction planning and structural analysis. Cast-in-place concrete is an example of a monolithic system, created by building temporary formwork and then placing concrete (and reinforcing materials) in the forms. The individual building elements (columns, beams, slabs) typically merge into a singular monolith when the concrete placed, so overlaps and intersections between these model elements is appropriate.
- What are the advantages of using 3D details compared to 2D details?
The focus of all detailing is to accurately convey your design intent to the people who will be constructing it. So, any technique that enables you to convey this intent more clearly and avoid any misunderstandings and mistakes is a better vehicle for communication. 3D views are often easier to understand than 2D sections callouts, which abstract a 3D model into a 2D representation where one dimension of the spatial information is lost or hidden. 2D details still serve an important role in construction documents, but for important connections where the spatial relationships may not be completely clear in a 2D view, 3D details can assist in explaining your design intent more clearly.
- When should exploded 3D views be used?
Exploded 3D views excel at explaining the relationships between elements or layers that sandwiched together very closely in the final assembly. Use exploded views to expose hidden or difficult-to-understand elements or layers to make it clearer to the people who will construct your design where one element starts and the next one begins.
Key Terms
The following key terms were used in this lesson:
Key Term | Definition |
Level of Detail | Level of detail refers to the degree of precision of the elements included in a BIM model.
Early in the design process, the model has a comparatively low level of detail. As the design process continues and specific details of the building elements are added to the model, the level of detail increases.
For an efficient work process, it is important to be aware of the appropriate or needed level of detail and model the building elements accordingly. |
Parts | Part elements in Revit support the construction modeling process by letting you divide certain elements from the design intent model into discrete parts. These parts, and any smaller parts derived from them, can be independently scheduled, tagged, filtered, and exported.
Parts can be used by construction modelers to plan delivery and installation of pieces of more complex Revit elements. |
Exploded view | An illustration depicting the disassembled individual components in proper relationship to their assembled positions.
Exploded views are often used to illustrate the details of multi-layered or multi-part assemblies. |