Page 53 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch02.qxd 9/29/05 5:01 PM Page 2.15

FABRICATION AND ERECTION*

FABRICATION AND ERECTION 2.15

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 dimen-
sions 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, 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, plate, and bar material 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 periodi-
cally. 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 mak-
ing, layout, punching and drilling, fitting up and reaming, bolting, welding, finishing, inspection,
cleaning, painting, and shipping.

2.7 BUILT-UP SECTIONS

Built-up sections are made up by a fabricator from two or more shapes or plates. Examples of com-
mon built-up sections are shown in Fig. 2.2. Built-up members are specified by the designer when
the desired properties or configuration cannot be obtained in a single hot-rolled section. Built-up sec-
tions can be bolted or welded. Welded members, in general, are less expensive because much less
handling is required in the shop and because of more efficient utilization of material. The clean lines
of welded members also produce a better appearance.
Cover-plated rolled beams are used when the required bending capacity is not available in a
rolled standard beam or when depth limitations preclude use of a deeper rolled beam or plate girder.
Cover-plated beams are also used in composite construction to obtain the efficiency of a nonsymmetrical
section.

FIGURE 2.2 Typical built-up structural sections.

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