Nail Estimating with Constructible Models


By Alistair Wells

Just about any architect would almost immediately realize the benefit of building 3D models to dazzle owners and win business. Yet the construction industry, with the exception of structural steel, has been slow to grasp the power of 3D modeling. Many of those in construction who have turned to Building Information Modeling (BIM) may not have mastered all the advantages, but one thing is certain:  General contractors and subcontractors who use 3D modeling can expect to substantially improve project performance and profit.
BIM is more than just modeling software controlled by one person on your team (who managed to grasp it). BIM is a process whereby construction team members benefit from sharing information and models and coordinating and communicating with each other.

The beauty of modeling in 3D is the incredible clarity it brings to the job. A 3D model improves planning, coordination, communication and construction by supplying the detailed project information needed to build a structure that meets the design intent. The more detail the model contains, the fewer construction problems arise. This high level of detail allows the kinks to be worked out of the plans well before the first excavator lumbers onto the jobsite.

Utilizing the model allowed a clear communication of drawing issues,
and helped solve problems earlier in the construction phase.

Does a concrete contractor, steel erector or any subcontractor have to be on a “BIM job” to benefit from using 3D models? The answer is no. In reality, a simple willingness to generate constructible models brings potential productivity and efficiency gains, which begin with pre-construction and estimating, to any organization.

The Big Deal about Detail
3D modeling and BIM should be all about detail:  putting every detail into the model and getting it back out for a specific use. This detail benefits the construction team in a variety of ways, including estimating. While architects and design engineers make good use of their BIM as a design tool for communicating their vision and confirming structural integrity, the construction information needed to actually build the structure is often sparse. Sometimes referred to as “design” BIM, these architectural models are virtually useless for the construction phase of a project. Yet, these models can become highly useful “constructible” Building Information Models when detail is added by the steel, concrete and MEP and other subcontractors.

Constructible BIM is, among many other things, an extremely powerful estimating tool that benefits general contractors and subcontractors for creating winning bids, accurately ordering materials, fabricating steel and streamlining remodels.

During preconstruction phase the structural model was developed for
logistics, planning, and quantity extraction. During construction, the
model is then utilized to coordinate all reinforcing and formwork

New Business Edge
Taking a cue from architectural firms, some construction companies are also using 3D models to win business. Unlike the “design” BIM models architects present to owners for “wow” effect, the preconstruction models created by companies like Adjustable Forms, a Chicago-based commercial concrete contractor, contain comprehensive steel and concrete detail. This detail allows Adjustable Forms to ensure the scope of the project is correct so they can produce accurate bids -- a practice that gives them a competitive edge to win more large-scale cast-in-place concrete structure business.

Working from 2D CAD design drawings, a PDF, or a 3D model supplied by the design engineer, the firm creates a preconstruction model and extracts material quantity information to an estimating tool. This process allows Adjustable Forms to accurately calculate the cost of a project, thereby reducing the contingency factor to produce a more competitive bid and mitigate the risk of a cost overrun.

The firm also uses a preconstruction model for drawing coordination, allowing them to resolve 90 percent of construction problems before breaking ground. It helps them identify issues with the design in the bidding process and bring these issues to the attention of the owner, general contractor and design team -- often before they’ve won the job -- instilling owner confidence and reinforcing the value of doing business with Adjustable Forms.

Accurate Estimates for Material Orders
Everyone wants the job to come in on budget, but the real trick is having enough of the right information to help that happen. The detailed information contained in a 3D model can be used not only to produce more accurate estimates but also to reduce cost overruns due to inaccurate manual material orders. It can help estimate the cost of correcting errors made during construction. It can also help to identify materials needed for exact specifications for a specific delivery date, to ensure the project isn’t delayed due to a shortage or miscalculation.

North Carolina-based concrete contractor, Wayne Brothers, was able to review rebar placement in the 3D model of the Sierra Nevada Brewery for accuracy and have the steel fabricated and shipped to the jobsite in just two weeks: twice as fast as it would have taken working off 2D drawings. Modeling the steel allowed Wayne Brothers to complete this phase of the project ahead of schedule, avoid missteps in the field, and minimize rebar waste.

A bridge on the brewery property had been designed based on a 50-year-old aerial topo map. Only when Wayne Brothers integrated the bridge model with a newly-created 3D model of the creek bed scan did it become apparent how far off the bridge design really was. A quick redesign allowed the contractor to order the correct amount of rebar, thereby reducing waste and resulting in a more coordinated, efficient project without any reworks. Why was Wayne Brothers using a 3D model? It wasn’t because the architect, engineer, or GC requested it. Wayne Brothers adopted the tools internally, and sees them as particularly significant for preventing problems like the one mentioned above.

Adjustable Forms uses constructible BIM to perform operational tasks faster, easier and more accurately. For example, by modeling shoring frames, the concrete contractor can extract the quantities by size for piece counts and send the report to the field. It’s a seamless process. Adjustable Forms also provides the model to its rebar detailers and fabricators to model the rebar detail and extract sizes and quantities for fabrication. Again, not driven by the demands of a GC but, instead, driven by their need to be productive.
Sarl Patrick Millet, a French structural engineering firm, was tasked with extensively remodeling and expanding a 60-year-old skating rink in the Alpine town of Gap, France. Because of the accuracy of the model detail -- such as the dimensions and quantities of the steel required for the project and the ability to generate accurate drawings from the model -- Millet issued its fabrication orders with confidence. Despite the project’s geometric complexity, there were no fabrication errors.

Barton Malow, a $1 billion national construction services company based in Southfield, Michigan, won the contract to design and construct two cast-in-place concrete silos, along with equipment and building foundations totaling over 10,000 yards of concrete. The field project manager used the model to directly order the correct amount of concrete for each pour from the jobsite.

For the Detroit Edison Energy Echo Wind Farm, a renewable energy source in Michigan, Barton Malow used information from the model to specify how to bundle the steel, so that it could be easily distributed at the jobsite and shave time off an aggressive installation schedule.

Improving Steel Fabrication Accuracy & Efficiency
The structural steel fabrication industry was quick to realize the early benefits of 3D modeling. For more than a decade, fabricators have created “intelligent” 3D models to more rapidly produce shop drawings, generate reports such as Bills of Material, and extract CNC data to drive machines in the shop -- virtually eliminating common errors.
The core needs of fabricators haven’t changed much over the years. In order to maximize profit, they need to be able to efficiently and cost effectively fabricate and deliver steel assemblies that can be erected onsite with no fit-up problems. To do that, they have to have quality, detailed information from which to fabricate.

It makes sense that being able to order steel pieces in the right sizes and quantities will decrease project costs by minimizing re-orders and stalls due to inaccurate or incomplete orders.

Barton Malow combines its extensive capability with the use of innovative technology. To expedite steel fabrication, the firm exports 3D model information to their fabrication software, allowing them to model bars, create drawings and send that information directly to the fabricator. Taking the information straight from the model ensures the fabrication drawings are correct and that they are only fabricating exactly what they need.

Steel fabricator ADF Group worked from a 3D model to fabricate the steel for Calgary’s St. Patrick’s Island Bridge. The company saved a substantial amount of time during the plate-cutting fabrication process as well as during the layout of the pieces. For example, ADF saved time and reduced the risk of errors and refabs by generating unfolded layouts for the plates from the model, which provided geometry, openings and the target points.

ADF also found that adding target points to the model saved time during the shop layout and geometry verification as well as during installation. The field crew could install the pieces in the “as-fabricated” condition, thereby eliminating fit-up problems and shop and field re-work.

Estimating for Remodel & Expansion Projects
Estimating for atypical jobs such as remodels and expansion projects can also be achieved with modeling. To do this, a 3D model is constructed using a combination of source data: 3D laser scans of the existing structure, drawings and as-built information. This process creates an accurate project scope and produces accurate material quantities.
Constructible BIM provides general contractors with accurate estimates to submit winning bids with low contingencies. It allows contractors to order materials to exact specifications and quantities at the right time to reduce waste. It illustrates the cost of mistakes on the budget and schedule. It also improves fabrication efficiencies. The ability to accurately estimate benefits both new construction and expansion and remodeling projects. Constructible BIM is especially valuable to complex, fast-tracked commercial projects.

Alistair Wells is Business Development for Tekla, a Trimble Company. Tekla Structures is an open BIM software package designed specifically to streamline the construction process by enabling general contractors, concrete contractors, steel, rebar and precast fabricators, steel detailers and structural engineers to build constructible Building Information Models that can be shared with the entire project team. Wells focuses on educating and growing awareness of the productivity benefits of 3D modeling and BIM in the concrete and construction industries by developing partnerships, growing Tekla’s involvement in industry associations, and listening to and working with Tekla customers. For more information, call 877-TEKLA-OK or visit

Tags: Costs, Estimating Construction

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