Page 41 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch02.qxd 9/29/05 5:01 PM Page 2.3

FABRICATION AND ERECTION*

FABRICATION AND ERECTION 2.3

After the detail drawings have been completed, they are checked by an experienced employee (a
checker) before being submitted to the engineer for approval. Drawings generated manually should
have virtually every depiction and dimension checked. Drawings generated by computer may be
checked mainly for input information and selected detail dimensions to assure accuracy. After
approval, the drawings are released to the shop for fabrication.

2.2 REQUIREMENTS FOR DRAWINGS

There are essentially two types of detail drawings, erection drawings and shop working drawings.
Erection drawings are used by the erector in the field. They consist of line diagrams showing the
location and orientation of each member or assembly, called shipping pieces, which will be shipped
to the construction site. Each shipping piece is identified by a piece mark, which is painted on the
member and shown in the erection drawings on the corresponding member. Erection drawings
should also show enough of the connection details to guide field forces in their work.
Shop working drawings, simply called details, are prepared for every member of a steel structure.
All information necessary for fabricating the piece is shown clearly on the detail. The size and location
of all holes are shown, as well as the type, size, and length of welds. While shop detail drawings are
absolutely imperative in fabrication of structural steel, they are used also by inspectors to ascertain that
members are being made as detailed. In addition, the details have lasting value to the owner of the struc-
ture in that they show exactly what was constructed, should future alterations or additions be required.
Design and detail drawings may be considered as a complex but important form of communica-
tion. The design drawings need to communicate clearly to the detailer, to avoid delays inherent in
requests for information, to avoid revisions necessitated by approval comments, and to avoid errors.
The most critical details are usually for connections. Connection design requires knowledge of
design loads, how forces are transferred through the structure, and calculated resistance of elements,
fasteners, and welds. It is important to know shop capability, limitations, and potential for fabrica-
tion economy. Many fabricators can economically provide connections suited to the equipment and
practices in their shops. Others desire as much detail information as possible. It is considered best
practice to provide general configuration and loads for common connection types and precise detail
for unusual or difficult connections. Awareness of the connection requirements is valuable for the
designer because there are cases in which member selection should be adjusted to provide room for
connections. In any case, the fabricator may request adjustment to accommodate shop limitations or eco-
nomic improvements. Where seismic loads are involved, the designer must provide all the necessary
detail to assure the building meets code requirements, including sizes of connection elements.
The following is a guide to information that should be provided by the designer on design drawings.
Simple Beam Connections. Reactions should be shown. Defining the reaction as a function of the
capacity of the beam causes problems when beams are selected for reasons other than strength, such
as stiffness, uniformity with other members, fitting detail, and attachment. If reactions are defined
generically in terms of beam capacity, reactions greater than that standard must be given, and those
significantly lower should be also. Horizontal forces (longitudinal transfer or drag forces) must be
given as well.

Moment Connections. Relative to simple connections, moment connections require extra labor,
either in the shop or the field or both. Moment connections can be made by welding the flanges to
the columns (and welding the webs to the columns for seismic loads), by bolting to welded connec-
tion plates, or with flange-welded end plates. In any of these configurations, large flange forces are
resisted by welds or bolts or both. Proper selection of the connection configuration depends on the
geometry of the frame, the size of the members, and regional practices and skill sets. Forces and
moments must be shown unless all connection details are shown.

Braced Connections. Forces in the braces and the beams must be known in order to size connec-
tions for bracing. Unnecessary work can be required if the connection designer does not know how

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.