Building Information Modeling, or 3D interactive modeling, has the potential to accurately capture every element involved in producing precast and promises to significantly decrease design time.
By Sue McCraven
When it comes to three dimensional (3D) interactive software technology, the construction industry has been criticized for not “getting with the program” and being slow to adopt new BIM (Building Information Modeling) systems. Other industries such as automotive, petrochemical, aerospace and electronics have been on board with direct digital exchange (DDE) of information using 3D models for some time. This article takes a look at the current use of BIM in the precast industry.
In design/build projects, BIM means conflict resolution “When I think of BIM in general, I think of conflict resolution in multi-system designs,” says Nick Burr, drafting supervisor for Tindall Corp., Spartanburg, S.C. For example, a structural precast building involving many trades is a particularly useful application of 3D modeling. In a structural precast building, mechanical and electrical ductwork runs through or adjacent to the precast elements. BIM, or 3D interactive modeling, makes it easy for all the various trades involved in a project to see, in real time, where the different systems are located. In a clash-free model, interferences or conflicts are automatically eliminated early in the design stage. Using BIM, all project collaborators are working with the same 3D plan; no change in one component can occur without all the players adjusting their systems simultaneously and with accuracy. In the past, in pre-BIM days, project conflicts usually became apparent during construction, with the inevitable result of costly change orders and delays for the owner.
For a precaster making many different and customized products that are not used in above-ground building systems, the usefulness of 3D modeling is sometimes not as apparent, but significant advantages still exist. Burr offers an example: “I recently modeled a very large custom precast pile cap with complex, congested reinforcing. 3D modeling helped us to identify and resolve potential conflicts in the steel design.” (See 3D renderings of heavily reinforced precast pile cap on pages 22 and 23.)
Transition from 3D model to the shop ticket
“We have experimented with several different 3D BIM software packages here at Tindall,” says Burr. “What we have found is that some software programs, in their present configurations, do not get us from the 3D model to the shop card, or shop ticket.” A shop ticket has all the information the fabricator needs to manufacture a specific precast product, including: types, weights and amount of materials to order; the mix design; accurate dimensions of all components; reinforcing steel type, weight and location; and number of plates or inserts.
“When we try to make that transition from the final BIM software model to the practical information needed for fabrication, we have found that some of the programs currently available are not particularly ‘user friendly’ for specific precast applications,” explains Burr. In other words, a precaster cannot realistically expect to take the BIM software off the shelf and expect it to function in specific precast applications without spending significant time tweaking or finessing the software.
“We do expect that the transition (from 3D model to shop card) will become easier the more we work with and adjust the software for our specific platforms,” says Burr. “Like anything new, it takes time and effort to work out all the bugs. I do believe, however, that BIM has great potential to exactly identify all the information needed for the precaster to accurately cost-out a project and to fabricate products with no hidden problems or surprises.”
Precast is a complex, custom and regional product
Precast is not as simple a product as structural steel, for example, and therefore not as readily amenable to BIM software. With structural steel, there are a finite number of standardized shapes and the product is made from one material; this is not the case with precast concrete. Precast is a flexible design material that can be made to fit any number of shapes and custom configurations. Precast production involves many different materials: steel, stone, cement, sand, water, admixtures and formwork. There are more parameters to capture when trying to model the factors involved in precast fabrication; in addition to product components, temperature and humidity are highly variable and critical considerations.
“The applicability of BIM technology depends completely on the precast product,” says Cal Van Ooyen, vice president of engineering, Kerkstra Precast Inc., Grandville, Mich. “For example, we produce hollow-core planks, a product that is essentially 2D. CAD (Computer Aided Design) works just fine for hollow-core. However, when you are building an entire structure out of multiple precast products, the complexity increases and the necessity of integrating all the trades and systems involved becomes more critical; this is where 3D modeling offers the most potential,” he says.
“One of the inherent BIM implementation issues for precast,” explains Van Ooyen, is that “it has many standard details, or parts and pieces that all need to be accurately captured and fed into a software program.” These pieces (connections, plates, reinforcing steel, openings) need to be captured to populate the software ‘library’ for BIM modeling to be productive and accurate. “Another important consideration for the precaster is the time and cost required to learn and train on the new software,” advises Van Ooyen. Ultimately, with a good library of parts and some experience, 3D modeling and BIM will help precasters continue to be competitive and grow with the industry.” Typical BIM software (one desk station) can cost about $25,000.
Michael Lawrence, senior regional designer, Hanson Pipe and Precast, Green Cove Springs, Fla., agrees with Van Ooyen. “Our industry is deceptive – from the outside, it looks simple, but every structure can be made in an almost infinite number of ways,” says Lawrence. “Unlike pipe, which is basically a commodity, precast structures are unique – each one will only fit in one spot. Changes to pipe size and angle can have a drastic effect
on the weight, and therefore the bill of materials used, on any piece of precast. This is particularly true of square and rectangular structures.”
Adding to precast’s complexity, manufacturing facilities in different regions often produce a number of concrete mixes – often based on regional materials and climate – and each mix design uses a specific list of components. “For example,” says Lawrence, “plants in Florida use limestone for aggregate, but in the Carolinas, granite is more prevalent. Getting one software system to be flexible enough to allow for all of these possibilities can be quite a challenge.”
BIM 3D interactive software is best suited to customized products. For a precaster who strictly produces a standard commodity like reinforced concrete pipe with a fixed bill of materials, says Lawrence, “there would not seem to be as much obvious benefit in BIM.”
BIM success requires time and commitment
“I have no way of knowing how Hanson stacks up against other precasters in terms of how advanced our 3D design software is,” says Lawrence, “but I can tell you that we have invested a lot of time and effort in trying to do it right.” Joan Blecha, who recently retired as president of Hanson’s Southeast Region and served as NPCA’s chairman of the board, spearheaded the drive to automate the BIM process.
“The trick with BIM,” explains Lawrence, “is in getting the information on the shop drawings to upload automatically to the manufacturing system. Nothing worked out of the box.” Hanson partnered with Neilsoft, a software vendor, to develop its system, which uses Inventor to create the 3D models (see precast schematics on pages 20 and 21) and sends the completed information to an Oracle platform. “For each piece of precast we design, that means capturing accurate quantities of concrete and steel,” says Lawrence.
“That allows us to design any shape product and accurately capture the number and volume of components in each piece,” says Jason Lambert,
engineering manager and software developer with Hanson. Hanson’s customized in-house BIM program enables managers to have a real-time handle on their entire inventory for all facilities in North America.
The goal: speeding up the design process
“Our first goal was to accurately capture all the component pieces in all of our precast products,” says Lawrence. “In this way, we were able to populate the database with all the required information, from exact dimensions to reinforcing steel numbers and weights to custom formwork. Our second goal is to significantly speed up the design process through BIM software. This is our first year working with the system, making sure we have exact material tracking in the software for our entire organization.” Hanson software engineers anticipate that as they become more proficient with BIM software, the company will be able to reduce precast design time by 25 percent to 35 percent, which means a significant savings in time and money.
Sue McCraven, NPCA senior technical consultant and Precast Solutions editor, is a civil engineer, technical writer and editor, and environmental scientist who has contributed numerous articles and studies to prominent scientific journals.