How Revit Structure Benefits the Construction Estimator
The Building Information Modeling (BIM) community is expanding to embrace the concept of total project delivery. One avenue of interest is sharing the Autodesk® Revit® Structure model with the construction estimator for bidding purposes. This article investigates the translation from Revit Structure to the estimating software Timberline by way of Autodesk® Quantity Takeoff (QTO).
The adoption of BIM into the workflow of the modern structural designer has changed the norm. I have personally experienced immense time savings in project design utilizing the RISA 3D exporter and contract document generation. Although I have seen the light, the next question is: How can others in the design and construction community also utilize BIM to improve their workflow?
One of the many possibilities relates to utilizing the BIM model in estimating practices. Traditionally, the estimating process has required a familiarization and accounting of the proposed building, as well as the materials required by the field staff to construct the project. This method is necessary to form a bid, yet it is inherently prone to human error.
To avoid these potential errors and omissions, designers have wondered whether this newly formed BIM model in software such as Revit Structure can translate to Timberline, popular spreadsheet-based estimating software from Sage. Fortunately, there is a workflow that promotes this beneficial sharing of information.
The stepping stone is Autodesk QTO, which can translate 3D BIM elements to a series of descriptors and quantities in the takeoff. QTO offers flexibility with traditional 2D project functionality, as well as 3D BIM projects. This flexibility provides the possibility for an all-encompassing tool in the estimator’s toolbox. Projects can be received in a number of formats, and the estimator has a single tool to accurately and efficiently account for the materials required to construct each project.
In terms of the BIM workflow, what makes QTO so powerful is its utilization of the dwf format. To everyday users such as project managers and scientists, the line between dwf and pdf is blurred, and I am often asked why designers have an affinity to the dwf file type. One of dwf’s many advantages is highlighted by QTO’s methods of data extraction.
The key is preservation: the dwf preserves the intelligence of the BIM model by storing the element properties with each of the objects, as seen in Figure 1.
Figure 1: Instance properties
Rather than a snapshot of a Revit view, the dwf maintains the material and geometric information key to the quantity takeoff. The result is a condensed file size with rich information you can use.
Autodesk Quantity Takeoff
Let’s see how QTO extracts this information. When you first open the QTO software and begin a new project, you are provided with a dialog box that allows the import of various files related to the project, including contract drawing sheets and overall 3D views of the model. You are also prompted to apply a catalog, as seen in Figure 2.
Figure 2: Catalog selection
This catalog, important from the perspective of translating to Timberline, sets up the groupings of materials. A typical material breakdown employs the CSI divisions that logically separate materials into similar working groups and provide a standardized framework across the industry. The catalog is fully customizable for applying preferences of categorization repetitively on all of your projects. This presents an opportunity for consistency amongst estimators and promotes further accuracy of the estimate. The default catalogs that come with the QTO software are shown in Figure 3.
Figure 3: Multiple catalog options
At this point, you can select the various files that are associated with your project in dwf, pdf, or image format. The pdf and image formats are used entirely for manual takeoff, while the dwf format provides the ability for shortcuts. When you begin the project with various drawings and views, they are all brought into the project and cached.
Toolbars with various purposes are located on the left side of the screen. One of these toolbars, named Documents, breaks down the project’s content into the different files that you initially brought in. This is a good way to traverse from one sheet to another for viewing purposes. Another available toolbar, named Model Tab, is similar to the family breakdown of the project browser from the Revit Structure model. An additional important toolbar, named Takeoff Tab, shows the work breakdown structure that was set up in the catalog selected during project creation. The location of these three tabs can be seen in Figure 4.
Figure 4: QTO GUI and important tabs
As with any software, there are multiple methods to obtain the same end result, but the use of a BIM model works effectively with the automatic takeoff tool. This tool can be found at the top of the screen and is shown as a building with a lightning bolt, seen in Figure 5. You can select the model you wish to takeoff, and this will populate a new category at the bottom of the takeoff window.
Figure 5: Automatic takeoff tool
The Family organization of Revit is far from the CSI division breakdown that may be desired for estimate purposes. It is then the estimator’s job to manually drag and drop the various instances found at the bottom of the takeoff window to the desired location in the work breakdown structure. The Takeoff palette with the unsorted model elements are shown in Figure 6.
Figure 6: Takeoff palette with unsorted items
Ultimately, this is a sensitive process that gives estimators the opportunity to apply their own preferences related to how an object is categorized. Since it is only a matter of dragging and dropping, and you may drag and drop multiple items at a time—making this a relatively easy and efficient process.
Once items are moved into the desired category—or during this process—you can adjust the properties specific to QTO. Most importantly, adjust the type that is to be applied to each item, for example the linear, area, volume, or count. This defines how the item is accounted for. Sorted items with their respective type are shown in Figure 7.
Figure 7: Sorted items with specified type
In order to obtain the quantity to be taken off, you may need to specify an equation that utilizes other known values such as length and height to calculate the desired quantity type, if it is not readily supplied with the instance data.
At this point, the quantity takeoff is complete, and the process of sending the information into Timberline is addressed. Because QTO is ultimately using an outlined format, you can also easily export to a spreadsheet type file. This can be done through the export tool, which is located under the file menu, as shown in Figure 8. This process will change the format of the QTO work breakdown structure.
Figure 8: Export selection
When this tool is selected, the option to convert into many different file types is given. For this case, a .pee file (a Timberline native file format) should be selected. This file type is available to those who already have Timberline installed on their machine. From here, you can easily open the file using the Timberline software.
Now, if you open the exported file in Timberline, you will see that the various groupings created in QTO retain. At this point, all of the materials are incorporated into the building in an organized way. You can then apply costs and derive products such as reports. The strength of Timberline is its built-up databases of material pricing information. In addition to pre-prepared databases bought with the software, estimators also have the ability to store geographic pricing information for more accurate estimates.
Playing to Strengths
The key is using each software product for its strengths rather than pushing the products into uncomfortable realms. For instance, QTO provides support for the entire estimating cycle with options to apply cost data to the quantity takeoff. QTO also has the ability to nicely display this information and perform the math for project costs. However, the user must input each cost without the support of an existing database and as a result, this process becomes tedious. Therefore, I find it’s better to utilize the strength of information from Timberline to increase the efficiency of your workflow.
It is important to note that there is possibility for complications in the Revit Structure-to-Timberline translation, as the communication between the structural designer and the estimator is crucial and also sensitive to misinterpretation. The two particular project scenarios that highlight issues of responsibility in communication are Design-Bid-Build and Design-Build type project deliveries.
In the Design-Bid-Build scenario there is a logical progression of information. The designer prepares a model containing the optimized structure along with contract documents ahead of the estimating and bidding process. The model could then theoretically be provided to the bidding contracting firms. The question surrounds how the BIM model might legally be shared with the bidding contracting companies to take advantage of the information-rich model.
The BIM model is the intellectual property of the designer and, therefore, the responsibility of the design firm. An issue may arise when considering the accuracy of the model that has been created. When frustration leads to work-arounds by designers and drafters, the end result is an inaccurate model. If the structural model is not a perfect virtualized replica of the building, then errors and omissions are likely to occur in the estimate. With a level of confidence being put into the validity of the model, a contractor can improperly bid the actual cost of construction. And when forces such as these cut into a contractor’s profits, discussions of change orders and litigation arise that are damaging to all involved.
The Design-Build project delivery situation has a different sequence. In this case the contractor and the designer are on the same team and as a result, the ownership of the model is less of an issue (keeping in mind that accuracy is still critical). The contractor and designer are bidding the project from square one, so the question becomes: How can you utilize a BIM model for an estimate at the conceptual bid level?
The answer to this question is likely project specific, but I believe that it is reasonable for either the structural designer or the estimator to put together a preliminary BIM model from which to takeoff. For me, the advantage to utilizing a BIM model is that in this modeling environment you can logically construct the project in fairly general terms from the ground up.
This may help you to visualize the construction sequence and completely account for all of the building materials. This visualization could cut down on potential errors and omissions and might also shed light on potential means and methods savings.
In addition to accuracy, having this nice 3D BIM model serves other purposes. In this changing time when BIM is relatively new, it could be impressive to show your model with 3D images or a building walkthrough in a presentation to the potential client. That client may appreciate your technical capabilities and be impressed with the dedication shown in the project before it’s even won.
Every project provides a unique scenario and sets of constraints, so I believe projects should be evaluated for the usefulness of a BIM model in the estimation process.
Advances in technology offer increased productivity and better efficiency for a project workflow. For structural engineers, the time savings is found in the design optimization and contract document preparation process. The concept of BIM inherently benefits the estimator by attaching a tremendous amount of useful information to a geometrically meaningful model. The process of quantity takeoff has always been to identify materials and their corresponding amounts in global space.
It seems intuitive that this type of overlap should be harnessed to provide time and cost savings. The key is to store this information as accurately as possible to properly depict the building at hand. With this dedication to accuracy and detail, the BIM model becomes a powerful tool for structural engineers and estimators alike.
The advantages of BIM are not limited to the designer; there are other inherent advantages of the information-rich file for members of the design and construction teams. Pushing the BIM process to a total project delivery level is the future of our field and, accordingly, extending the benefits to the entire project team is critical.
Sean Woods is a Structural Design Engineer at O’Brien & Gere (Syracuse, New York, USA) and a graduate student in the Sustainable Construction Management and Engineering Department at SUNY ESF. Sean has played an active role in implementing the Revit Suite of products as well as Navisworks at O’Brien & Gere. He can be reached at Sean.Woods@obg.com.