Foundations and Anchor Bolts:
Exact location of anchor bolts is essential to construction
Marcy Marro, Managing Editor,
Posted
07/31/2012
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:
- Reduce foundation energy loss and save on energy costs-year
after year
- Protect against moisture problems
- Provide an additional layer of drainage protection when
installed on the exterior of foundation walls
- Protect the waterproofing membrane on the exterior of
foundation walls
- Reduce the potential for interior condensation by keeping the
temperature relatively constant
- Use the thermal mass of the concrete to store and radiate heat
as needed
- Minimize frost upheave leading to possible cracking of the
floor slab
"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.
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