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.
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):
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.
- ACI Committee 315, ACI Detailing Manual, SP-66, American Concrete Institute, Farmington Hills, MI, 2004, 175 pp.