Hot-rolled sections produced by rolling mills and delivered to the fabricator include the following designations: W shapes, wide-flange shapes with essentially parallel flange surfaces;
S shapes, American Standard beams with slope of 162⁄3% on inner flange surfaces;
HP shapes, bearing-pile shapes (similar to W shapes but with flange and web thicknesses equal), M shapes (miscellaneous shapes that are similar to W, S, or HP but do not meet that classification), C shapes (American Standard channel shape with slope of 162⁄3% on inner flange surfaces), MC shapes (miscellaneous channels similar to C), L shapes or angles, and ST (structural tees cut from W, M, or S shapes). Such material, as well as plates and bars, is referred to collectively as plain material.
To fulfill the needs of a particular contract, some of the plain material may be purchased from a local warehouse or may be taken from the fabricator’s own stock. The major portion of plain material, however, is ordered directly from a mill to specific properties and dimensions. Each piece of steel on the order is given an identifying mark through which its origin can be traced. Mill test reports, when required, are furnished by the mill to the fabricator to certify that the requirements specified have been met.
Steel shapes, such as beams, columns, and truss chords, that constitute main material for a project are often ordered from the mill to approximately their final length. The exact length ordered depends on the type of end connection or end preparation and the extent to which the final length can be determined at the time of ordering. The length ordered must take into account the mill tolerances on length. These range for wide-flange shapes from 3⁄8 to 1⁄2 in or more, depending on size and length of section (see ASTM A6). Beams that are to have standard framed or seated end connections therefore are ordered to such lengths that they will not be delivered too long. When connection material is attached, it is positioned to produce the desired length. Beams that will frame directly to other members, as is often the case in welded construction, must be ordered to such lengths that they cannot be delivered too short. In addition, an allowance for trimming must be added. Economies are achieved by limiting the number of lengths shipped, and current practice of some producers is to supply material grouped in length increments of 4 in.
Wide-flange shapes used as columns are ordered with an allowance for finishing the ends.
Items such as angles for bracing or truss-web members, detail material, and light members in general are ordered in long pieces from which several members can be cut.
Plate material such as that for use in plate-girder webs is generally ordered to required dimensions plus additional amounts for trim and camber.
Plate material such as that for use in plate-girder flanges or built-up column webs and flanges is generally ordered to the required length plus trim allowance but in multiple widths for flame cutting or stripping to required widths.
The dimensions in which standard sections are ordered, i.e., multiple widths, multiple lengths, etc., are given careful consideration by the fabricator because the mill unit prices for the material depend on dimensions as well as on physical properties and chemistry.
Computers are often used to optimize ordering of material.
ASTM A36, A572, A588, A514, A709, A852, A913, A992 and A709 define the mechanical properties, chemistry and permissible production methods for the materials commonly used in structural steel for buildings and bridges. The common production requirements for shapes and plate are defined in ASTM A6. This standard includes requirements on what testing is required, what is to be included in test reports, quality requirements such as surface imperfection limits, and tolerances on physical dimensions. A6 also contains a list of shape designations with their associated dimensions. Not all shapes defined in A6 are produced by a mill at any given time. While most of the shapes listed are available from more than one domestic or foreign mill, some shapes may not be available at all, or may be available only in mill quantities (anywhere from 20 to 200 tons) or may be available only with long lead times. The AISC publishes information on the availability of shapes periodically.
When rolled shapes are not available to suit a given requirement, shapes can be built in the fabricating shop.
Fabrication of standard sections entails several or all of the following operations: template making, layout, punching and drilling, fitting up and reaming, bolting, welding, finishing, inspection, cleaning, painting, and shipping.