Civil Engineering Reference
In-Depth Information
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Avoid manual arc-welded splices of reinforcing bars in the field wherever possible, particularly for
smaller projects.
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A frequently occurring construction problem is having to make field corrections to reinforcing bars
partially embedded in hardened concrete. Such “job stoppers” usually result from errors in placing or
fabrication, accidental bending caused by construction equipment, or a design change. Field bending
of bars partially embedded in concrete is not permitted except if such bending is shown on the design
drawings or authorized by the Engineer (ACI 7.3.2). ACI R7.3 offers guidance on this subject. Further
guidance on bending and straightening of reinforcing bars is given in Reference 8.2.
8.3
REINFORCING BARS
Billet-steel reinforcing bars conforming to ASTM A 615, Grade 60, are the most widely used type and grade
in the United States. Combining the Strength Design Method with Grade 60 bars results in maximum overall
economy. This design practice has made Grade 60 reinforcing bars the standard grade. The current edition of
ASTM A 615 reflects this practice, as only bar sizes No.3 through No.6 in Grade 40 are included in the
specification. Also listed are Grade 75 bars in sizes No.6 through No.18 only. The larger bar sizes in Grade 75
(No.11, No.14, and No.18) are usually used in columns made of high strength concrete in high-rise buildings.
The combination of high strength concrete and Grade 75 bars may result in smaller column sizes, and, thus,
more rentable space, especially in the lower levels of a building. It is important to note that Grade 75 bars may
not be readily available in all areas of the country; also, as mentioned above, No.14 and No.18 bars are not
commonly available in distributors' stock. ACI 3.5.3.2 permits the use of Grade 75 bars provided that they meet
all the requirements listed in that section (also see ACI 9.4).
When important or extensive welding is required, or when more bendability and controlled ductility are
required (as in seismic construction*), use of low-alloy reinforcing bars conforming to ASTM A 706 should be
considered. Note that the specification covers only Grade 60 bars. Local availability should be investigated
before specifying A 706 bars.
8.3.1
Coated Reinforcing Bars
Zinc-coated (galvanized) and epoxy-coated reinforcing bars are used increasingly for corrosion-protection in
reinforced concrete structures. An example of a structure that might use coated bars is a parking garage where
vehicles track in deicing salts.
Zinc-coated (galvanized) reinforcing bars must conform to ASTM A 767; also, the reinforcement to be coated
must conform to one of the specifications listed in ACI 3.5.3.1. Bars are usually fabricated before galvanizing.
In these cases, the minimum finished bend diameters given in Table 2 of ASTM A 767 must be specified.
ASTM A 767 has two classes of coating weights of surface. Class I (3.0 oz./Sq ft for No.3bars and 3.5 oz./sq
ft for No.4 and larger bars) is normally specified for general construction. ASTM A 767, requires that sheared
ends to be coated with a zinc-rich formulation. Also when bars are fabricated after galvanizing, ASTM A 767
*
ACI 21.1.5.2 specifically requires reinforcing bars complying with ASTM A 706 to be used in frame members and in wall
boundary elements subjected to seismic forces. Note that ASTM A 615 Grade 40 and Grade 60 bars are also allowed if they
meet all of the requirements in the section.
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