When it comes to the erection of metal building systems, one of the most important aspects is the location of the anchor bolts in the foundation. The incorrect placement or embodiment of anchor bolts can lead to costly errors, or even fatal accidents.
While metal building manufacturers will supply an anchor bolt plan showing the location of each anchor bolt on the slab, along with the framed opening locations, reactions and bolt diameters, for a new metal building, it is up to the building owner to have an engineer design a proper foundation for the building.
Scott Thomson of Salsa Steel Corp., Chowchilla, Calif., a firm that specializes in foundation design for metal buildings, even lists misplaced anchor bolts as the number two problem in the “Top 10 Countdown to the Most Costly Foundation Mistakes” flyer he sends out to prospective customers. (Number one is the use of an over-designed foundation.)
Responsibility for Anchor Bolts
“Anchor bolt placement is an issue because most people don’t realize who’s responsible,” says Gary T. Smith, president of steel building erector Thomas Phoenix International Inc., Eastampton, N.J. Smith, who is on the national board of the Metal Building Contractors and Erectors Association, says that there is some gray area as to who is ultimately responsible for anchor bolts settings-the concrete contractor or the steel erector. When discussing the issue, Smith cites the Metal Building Systems Manual produced by the Metal Building Manufacturers Association.
According to section 6.2.2., “Work Usually Not Included in Erection,” the erector is not responsible for “foundation, concrete or masonry work” (sub item 3), along with the “setting or inspection of setting of anchor bolts, leveling plates, templates, column base tie rods or any item to be set or imbedded in concrete masonry” (sub item 4).
However, Smith notes that in section 6.4, “Concrete Slab, Foundation and Anchor Bolt Setting,” the manual says “the End Customer is responsible for all additional costs resulting from errors in the concrete slab and foundation or in the settings of anchor bolts, except where the concrete slab and foundation are constructed by the Builder. The Erector is responsible for ensuring that concrete dimensions and anchor bolt locations are correct before setting any steel.”
Smith explains that this means it is the responsibility of the concrete contractor to ensure that the anchor bolts, leveling plates, templates, and other items are set and embedded into the concrete correctly. However, once the concrete contractor has signed off on the foundation, it is the responsibility of the steel erector to make sure that the concrete dimensions and anchor bolt locations are correct before setting any steel. If there is a problem, the erector needs to go back to the general contractor and the concrete contractor to fix it, before moving forward on the building’s erection.
Ensuring Anchor Bolt Locations
Wes Brooker, market development manager at American Buildings Co., Eufaula, Ala., admits that while most metal building manufacturers don’t have anything to do with the foundations, anchor bolts are an issue that they deal with on a fairly regular basis. As he explains, when there is an issue with the anchor bolts matching the holes in the framing, there are two options-either the anchor bolts have to be removed from the concrete by the use of a jack hammer and redone, or the building’s framing needs to be changed. Either way, when anchor bolts are embedded incorrectly or in the wrong location, the mistake ends up becoming costly to fix, and can cause delays in the project’s time frame.
According to Brooker, approximately 70 percent of American Building’s projects are designed using Tekla Structures, a building information modeling (BIM) software program that creates 3-D models of buildings, from Kennesaw, Ga.-based Tekla Inc., a Trimble company.
“Tekla Structures allows [Brooker’s] team to actually design and detail all of the components of a metal structure,” says Jarrod Krug, marketing communications is the marketing communications manager in the building construction division of Trimble Navigation Ltd., Sunnyvale, Calif. “All the way from the bolts, clips, the I-beams, columns-everything is detailed and the specification data for the manufacturers are even located in that model.”
Once the BIM model in Tekla Structures is completed, the user can export the exact location of the anchor bolts, or field points, to Trimble’s Field Link for Structures tablet, which when interfaced with the Robotic Total Stations (RTS), allows for precise field-layout of the points. “We can actually locate and define those anchor bolt locations and bring them into the tablet device that allows you to interface with a RTS, allowing for laser-guided precision of specific elements within the model,” explains Krug.
After the anchor bolts have been placed, the RTS system can be used again to confirm the placement of the anchor bolts, comparing the actual locations to those in the BIM model. This process, Krug adds, is full-circle in terms of defining and comparing what’s in the model in digital form with what’s actually in the building’s physical form.
**Top two photos courtesy of Krudwig & Associates Inc., De Soto, Kan.; Bottom photo courtesy of
Trimble Navigation Ltd.
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Beyond the Bolts Well-designed buildings require careful attention to detail beyond just making sure the foundation’s anchor bolts are embedded into the concrete in the proper location. One of the biggest problems with foundations in metal buildings is ensuring the concrete slab is properly insulated.
Most metal buildings are built slab-on-grade where the concrete slab is poured on a prepared underlying substrate. Since concrete is a highly heat-conductive material, insulation is recommended around the perimeter footing as well as under the floor slab. Doug Todd, North American market manager at Midland, Mich.-based Dow Building Solutions, explains that an uninsulated or poorly insulated floor is susceptible to heat loss in two ways-horizontally though the footing into the earth below grade, and vertically though the concrete wall and into the air above grade.
Depending on the building’s design requirements, insulation can be added on the exterior or interior of the foundation-as well as under the slab. “Metal is highly conductive to heat transfer so where metal is left exposed it can become a conduit for heat loss through the building envelope,” says Todd. “Generally the focus is on heat loss through the walls and roofs-forgetting the heat loss potential through the slabs and foundations.”
By adding a continuous layer of insulation, such as Dow’s extruded polystyrene STYROFOAM Brand Insulation, on either the exterior or interior of the footing wall and under the slabs, both the vertical and horizontal heat flow through the wall can be slowed to:
“In many cases, installing the insulation around the exterior of the foundation is easiest as it combines insulation value while protecting the waterproofing material and doesn’t take up any usable interior space,” explains Todd. “In this type of application, just make sure that any above-grade insulation is protected. For insulation placed under the slab-ideal in radiant floor applications-the designer must take into account the design loads. High loading-from mechanical equipment or high traffic-may require higher compressive strength insulation. With exterior applications, check that the insulation can withstand moist environments without compromising durability.”
“Regardless of the application, the insulation must be able to outperform in a high-moisture environment and deliver long-term, high-R-value performance,” Todd adds.
To learn more, visit www.buildings.dow.com. |
