1.4. Other General Information

1.4.1. Color combinations are commonly used to indicate various steel grades. Where are these color combinations established?

Colors that identify the various grades of structural steel used to be established in ASTM A6/A6M.The requirement for color coding has been eliminated and is no longer required

1.4.2. Where are chemistry requirements for structural steel specified?

Chemistry limitations and requirements are specified in certain ASTM specifications for structural steels, such as ASTM A36, A572, A588, A992, etc. Steel producers are required to report steel chemistry for each heat of steel produced on an MTR (see FAQ 1.3.1).

1.4.3. Structurally, is there a difference between a ½ × 4 bar and a ½ × 4 plate?

Structurally, no. Furthermore, plate is becoming a universally applied term. However, the historical classification system for such structural material would suggest the following physical difference: All four sides of a ½ × 4 bar would be rolled edges—i.e., the mill rolled it to that thickness and width. A ½ × 4 plate will have been cut from a ½-in. plate of greater width either by shearing or flame cutting.

1.4.4. What are the common length limits on structural steel members as ordered from the mill?

Common mill lengths range from 30 ft to 65 ft in 5-ft increments. However, because individual mill practices and standards vary, it is best to consult with individual mills directly. When steel is purchased from a service center, the selection of available lengths may be further limited. Additionally, the method of shipment may also limit the available length.

1.4.5. What are the sizes of fillets for W-shapes?

Per Section 12.3.1 of ASTM A6, fillet radii are an unspecified dimension. As such, they are manufacturer-specific. Contact an individual manufacturer directly for additional information. AISC performs a periodic survey of producers’ practices to determine the minimum and maximum fillets used in shape production. The results of that survey are used to establish values in the AISC Manual, such as T, kdes, kdet and k1, which are detailing values. T, kdet and k1 are based upon the largest reported fillet radius, which ensures that potentially large fillet radii will not lead to fit-up problems. kdes is a design value based upon the smallest reported fillet, which ensures that the strength will not be overestimated in a design calculation no matter what the fillet size.

1.4.6. What is the difference between a round HSS and a pipe?

Round HSS are intended to be used as structural members.
Pipe, though sometimes used as structural members,
is intended to be used for mechanical and pressure applications.
As used in the AISC Steel Construction Manual, steel pipe
and round HSS are manufactured to meet different ASTM
standards. Steel pipe is made to requirements in ASTM A53
Grade B (Fy= 35 ksi).

Pipes up to and including NPS 12 are designated by the
term Pipe, nominal diameter (in.) and weight class (Std., xStrong,
xx-Strong). NPS stands for nominal pipe size. For
example, Pipe 5 Std. denotes a pipe with a 5-in. nominal diameter
and a 0.258-in. wall thickness, which corresponds to
the standard weight series. Pipes with wall thicknesses that
do not correspond to the foregoing weight classes are designated
by the term Pipe, outside diameter (in.) and wall thickness
(in.), with both expressed to three decimal places. For
example, Pipe 14.000·0.375 and Pipe 5.563·0.500 are proper

Round HSS are usually ASTM A500 Grade C (Fy= 46 ksi).
They are available in cross sections matching each of the cross
sections for ASTM A53 Grade B steel pipe. For example, an
HSS 6.625×0.280 has the same dimensional properties as a
Pipe 6 Std. Additionally, ASTM A500 HSS can be obtained in
many more sizes with periphery not exceeding 64 in. and wall
thickness not exceeding 5⁄8 in.

One important difference, especially from an architectural perspective, is that round HSS will have an outside diameter equal to the nominal diameter, but the outside diameter of a pipe will vary depending on its thickness. The tolerances on A500 HSS also tend to be tighter than those on A53. For example A53 requires only that the pipe be reasonably straight, where A500 places a specific tolerance on straightness. Also, A53 specifically allows dents with depths up to the lesser of 10% of the pipe diameter or ¼ in.

1.4.7. What is the difference between a tube shape (TS) and HSS?

Structurally, there is no difference. The Steel Tube Institute, an organization representing the manufacturers of hollow structural sections, initiated the change from “tube” to “HSS” in 1997 to conform to their designation practices. Thus, “TS” is simply an outdated way to specify “HSS.

1.4.8. What is the appropriate call-out for HSS?

Rectangular HSS are designated by the mark “HSS,” overall
outside dimensions (in.) and wall thickness (in.), with all
dimensions expressed as fractional numbers. For example, a
square HSS should be designated as HSS8×8×3⁄8 (instead of
the old TS8×8×3⁄8). A rectangular HSS should be designated
as HSS5×3×3⁄8 (instead of the old TS5×3×3⁄8). Round HSS are
designated by the term “HSS,” nominal outside diameter (in.)
and wall thickness (in.) with both dimensions expressed to three
decimal places. For example, a round HSS should be designated
as HSS5.563×0.258.

Note that ASTM A53 steel pipe designations (e.g., Pipe 5
Std., Pipe 5 x-strong, etc.) are designated differently than round

1.4.9. What is COR-TEN steel?

COR-TEN is a U.S. Steel trade name for ASTM A588 weathering steel. The most common weathering material is ASTM A588 Grade A. The proper specification of weathering steel is by ASTM designation, not the U.S. Steel trade name.