Industry Insights
In the commercial building industry, advances in the capabilities of Autodesk® Revit® have created a trend toward the use of Revit as a tool for shop drawing creation. From its inception, Revit was geared toward building designers (architects, structural engineers, and mechanical engineers) as a BIM tool for design, documentation, and collaboration within design teams. Design teams have typically modeled up to LOD 300 (per BIMForum Specifications), at best.
In recent years, Autodesk software has made a push into fabrication, to help link the design and construction phases of the commercial building industry. One way that Autodesk made an immediate impact is by acquiring Advance Steel as a true steel detailing platform. The other approach Autodesk took was to enhance the tools embedded in Revit to enable users to produce fabrication models and shop drawing natively in Revit. The addition of the Parts and Assemblies tools, robust rebar modeling and documentation tools, and the addition of a steel connection module in Revit 2017 have given Revit users a toolbox to allow them to push models past LOD 300 and into LOD 350 and 400 for structural elements. Additionally, third-party add-ins for Revit have enhanced the ability to use Revit for fabrication modeling and shop drawing creation for structural elements.
There is a trend in the commercial building construction industry toward structural engineering firms, outside consultants, subcontractors, and contractors leveraging the software enhancements to push models from design into fabrication and construction. In the traditional approach, structural models created in the design phase have not typically been used by fabricators or builders, apart from some Navisworks coordination. Instead, fabricators and builders have either used traditional 2D methods to create structural shop drawings, or created new 3D models and shop drawings from scratch. This has created a tremendous opportunity for structural engineering firms and outside consultants to use structural design models as a starting point, add a higher level of detail to structural components, and use the same model to create shop drawings.
Structural engineering firms have started to offer detailing services for structural components on projects for which they are the Engineer of Record. This gives them a competitive advantage by offering a streamlined service that has the potential to compress the construction schedules. Structural firms can start detailing during the later stages of design, rather than after design is complete. From a construction team perspective, this helps prevent the drop-off of knowledge and intent from design into construction, and can reduce schedule and cost.
This article will briefly discuss the trends toward using Revit to help with shop drawing creation and fabrication data for steel, cast-in-place (rebar shops and lift drawings), precast concrete, and metal stud framed buildings.
Rebar Shop Drawings and Fabrication Data
For the last five years or so, I’m sure you have noticed that when you run through the annual “What’s New in Revit Structure” blog posts and videos, there are always structural reinforcement topics. Little by little, over the last few years, Autodesk has made Revit into a true rebar detailing software.
The big leap came a few years ago when Autodesk introduced automatic bar numbering and partitions. With this tool, Revit gained the ability to identify rebar with the same size, shape, and bend segments, and give them the same rebar number. Other annotation tools such as bar presentation controls and multi-rebar annotation have made the creation of rebar shop drawings much more efficient.
Similarly, Autodesk introduced rebar modeling tools over the last several years that allow users to populate their models with rebar much more easily. They have enhanced the rebar constraints dialog, introduced varying length rebar sets, and added rebar couplers.
Additionally, there are several software packages out there to help with modeling and annotating rebar in Revit. SOFiSTiK is particularly useful in the annotation and creation of rebar shops. Their plug-in, as well as Graitec’s PowerPack, seek to help engineers take the results of their analysis into actual modeled rebar within Revit.
In the U.S. commercial building construction industry, rebar fabricators have typically been responsible for the rebar detailing scope of work. However, in many European countries, that responsibility has been that of the structural Engineer of Record. With the native tools in Revit, U.S. structural engineers have started to realize that they can offer rebar modeling and detailing as an add-on service for their projects. While there is a learning curve, shift in risk, and it takes the right project participants and relationships, structural engineers have started to offer this on their projects. For many projects, the potential schedule and material savings are significant. Because the structural engineers are most familiar with the project and can leverage the Revit models created in the design phase, they are well suited to push the rebar portion of the model into the fabrication and construction phase.
Figure 1: Rebar modeled in Revit
CIP Concrete Lift Drawings
For cast-in-place (CIP) concrete, subcontractors and self-performing general contractors have for years been creating lift drawings, slab edge drawings, and formwork using everything from hand sketches, to Bluebeam, to AutoCAD. To create an accurate and useful concrete lift drawing, information from the structural drawings, architectural drawings, and shop drawings from various other trades (such as stair and elevator shops, MEP penetration, steel embeds, and glazing system embeds) must all be brought together and incorporated. A current trend in the industry is to use Revit models to perform this task. The end result is highly coordinated, clear, and intuitive lift drawings that enhance coordination and improve field productivity.
Again, a great starting place for these lift drawings is to use Revit models from the design teams as a background from which to build the accurate concrete geometry. Often, structural and architectural Revit models may only show concrete geometry to a LOD of 300 or 350. For instance, slab-on-grade pour-downs may not be shown at door thresholds, accurate sloping and stepping of slabs may not be modeled, doors and windows may not be modeled to the correct rough openings, and architectural and structural may not be completely coordinated. However, concrete professionals and outside consultants are increasingly using design models as a starting place for their LOD 350 or 400 concrete models.
Figure 2: Concrete lift drawing isometric from Revit
Steel Detailing
Structural steel detailing is one segment of structural fabrication that has been using 3D modeling and BIM to create shop drawings for years. Detailing software such as SDS/2 and Tekla have been the most common for the commercial building industry in the U.S. in the past, and Advance Steel was very common in Europe and elsewhere. A couple of years ago, Autodesk acquired Advance Steel, and added a true steel detailing software to their product lineup and customer workflows.
Partially because of Autodesk’s acquisition of Advance Steel, partially because of better interoperability between Revit and other steel detailing software, and also because of better IFC file transfers, structural engineering firms have been able to push into steel detailing services. Some larger firms have in-house steel detailing departments, while others partner with structural steel fabricators and detailers to offer steel detailing services on projects for which they are the Engineer of Record. Smaller firms and outside consultants have also started to realize that with their current tools at hand, they can offer steel detailing services as an expansion of their current workflows.
The seamless interoperability between Advance Steel and Revit has enabled a workflow that allows design teams and steel detailing teams to share models quickly and easily. With the new tools available in Revit 2017, structural engineers can now quickly and easily populate their Revit models with steel connections from extremely robust pre-defined templates, which work very much like those in Advance Steel. Then, the model can be sent to Advance Steel to do the “heavy lifting” required in steel detailing, such as the annotation and documentation.
For smaller structural steel framing projects or miscellaneous metals scopes of works, some design firms have provided steel shop drawings directly from native Revit. The Assemblies tool in Revit is geared perfectly toward steel detailing, as members can be assembled together with their corresponding connection elements and annotated and scheduled accordingly. Though tedious and difficult on a large job, it is possible to create steel shop drawing directly in Revit. Some add-ins are available, such as Smart Assemblies from AGACAD, to help automate some of these tasks.
Figure 3: Steel connection module in Revit 2017
Precast Concrete
Unlike rebar and steel framing, precast concrete members are not standardized and vary by each individual fabricator. Because of this, precast concrete has been largely left out of advances in the tools within Revit for fabrication level modeling and shop drawing production. However, because of the variance in products, geometry, and preferences between fabricators, design teams have a hard time defining accurate precast geometry and layout during the design phase. Also, general contractors are asking precast fabricators for fabrication-level models more and more, as a means to coordinate with other trades.
Because of this, precast concrete manufacturers and their outside consultants have begun to take the plunge into fabrication-level modeling within Revit. The native Parts and Assemblies tools in Revit were one of the catalysts to allow this to happen, as precast members and their connection elements are grouped together and scheduled as assemblies for piece drawing purposes. Additionally, some Revit add-ins have been developed that are geared toward the precast industry, such as AGACAD’s Precast Concrete Suite, IDAT GmbH’s tools, and Edge^Revit.
One of the big challenges facing precasters when switching to Revit is building libraries of families for all of their various products, connection elements, raw material, and inserts. Then, this content must contain data that accurately feeds into other processes internally, such as material ordering, production scheduling, quality control, shipping, and erection. Though challenging, the payoff is great, and there is a trend in the precast industry toward adopting Revit.
Figure 4: Precast fabrication model in Revit
Metal Stud Framing
Some firms are also using Revit for to create shop drawings for cold-formed steel studs (CFS). Here in Colorado, cold-formed metal framing for walls is typically a delegated design item with the shop drawings as a deferred submittal. The subcontractor is then responsible for securing the engineering and shop drawings for the CFS members. Increasingly, structural engineering firms are taking on that responsibility and offering the engineering and shop drawings for these elements. Because they already have a geometrically accurate Revit model (included the architect’s walls linked in), it is easy for engineering firms to take their models a step further and include the CFS framing. This puts them at a competitive advantage over an outside entity that would have to re-create the geometry, and also gain the knowledge of the building and loading.
Though useful in some cases, creating a model with individual CFS members is not necessary. The structural EOR can use existing elevation views created and define layouts to create simple and efficient shops drawings. Several metal stud manufacturers have Revit families and details available for download to help with this. If Bills of Material (BOMs) for the studs and connectors are desired, then there are add-ins for Revit to help with modeling and shop drawing creation. StructSoft and AGACAD both have created tools that work well for this.
Summary
Over the last few years, improvements to Revit and the availability of add-ins have put fabrication modeling and shop drawing creation tools in the hands of those best suited to use them—the structural engineers. Because of this, the trend in the industry has been for structural engineering firms and consultants to leverage these tools, as well as their project and technical knowledge, to start offering detailing services for structural elements. While different challenges and opportunities exist for each type of structural element you now have the software available to dive in and give it a shot!
