By Dick Birley, President of Condor Rebar Consultants, Inc.
First published in Concrete International Magazine, January 2009
Steel mills supply reinforcing bars in standard stock
lengths, commonly known as mill lengths. Fabricators
supply reinforcing bars in cut or detailed lengths.
Normally, No. 5 (No. 16) and larger bars are available
in standard mill lengths of up to 60 ft (18 m), and No. 4
(No. 13) and smaller bars are available in mill lengths of
up to 40 ft (12 m). Some fabricators, however, may stock a small quantity of larger bar sizes, usually No. 11 (No. 36) and larger, in lengths over 60 ft (18 m).
Although splices are typically used to overcome stocklength
limitations, there are occasional situations where
splices would be inconvenient or unacceptable. There are
also situations where it would be more efficient to have
the steel mill fabricate bars that are longer or shorter
than the standard stock lengths. Fortunately, within
certain limitations, it’s possible to vary the length of the
bar produced at the mill.
Limitations
Before reinforcing bars that exceed the standard mill
length are detailed or scheduled on design documents,
there are a few important limitations to consider.
First, check availability. Fabricators and mills may
have some flexibility, so given enough lead-time and
sufficient quantity, bars of any specific length (longer
or shorter than stock length) may be ordered directly
from the mill. There are regional differences in the
availability of special-length bars, however, so again—
check with fabricators and mills.
If overlength reinforcing bars are required on a project,
the designer should try to avoid using overlength bars with
hooks or bends. Bending overlength bars may present
difficulties for the fabricator, and the required special
accommodations in the fabrication shop could be costly.
Issues may also arise over the shipping of overlength
bars. The standard length of a rail car is about 65 ft
(20 m). The lengths of flatbed semitrailers used on U.S.
highways can range from 48 to 60 ft (15 to 18 m), but length
restrictions vary by state. Access to the site may also be an
issue. Although long tractor-semitrailer combinations can
usually maneuver with relative ease on large industrial sites,
they may have difficulty accessing tight urban sites.
The transportation of overlength reinforcing bars
bent in an arc or an L-shape must also be considered.
Standard trailer bed widths range from 8 ft 0 in. to 8 ft
6 in. (2.4 to 2.6 m). Figure 1 illustrates a 7 ft 4 in. (2.2 m)
maximum reinforcing bar width for a common 8 ft 0 in.
bed width (the 8 in. [200 mm] difference accounts for
the bundling of several bars in a shipment).
For an arcshaped
bar, the maximum bar length is a function of the
bending radius R and the maximum reinforcing bar width
H of 7 ft 4 in. (2.2 m):
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For an L-shaped bar, the maximum longer leg length is
a function of H and the length of the shorter leg S:
Typical results for Eq. (1) and (2) are tabulated in
Reference 1.
Overlength reinforcing bars can strain the limits of
on-site lifting equipment. Bar bundles may have to be split
to reduce the weight of each lift, and
special chokers or spreader beams
may be needed to prevent excessive
bending of the bars under self-weight.
Maneuvering bar bundles around
onsite obstacles and placing bars in
the forms can also be issues, and
placed bars themselves can create
obstacles if they extend past a
construction joint.
Going to Great Lengths
Using overlength reinforcing bars
can have both benefits and drawbacks.
Designers need to determine the best
option, taking into consideration the
affected mills, fabricators, transportation
systems, and site conditions. Even
if it can be done, it may be better to
find an alternate solution.
References
1. ACI Committee 315, ACI Detailing
Manual, SP-66, American Concrete Institute,
Farmington Hills, MI, 2004, 175 pp.
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