Structural steel is one of the basic materials used
in the construction of frames for most industrial
buildings, bridges, and advanced storage structures.
The plans, sequences, and required materials are predetermined
by engineers and are then drawn up as a set of blueprints.
This article describes the terminology applied to structural
steel members, the use of these members, the methods by which
they are connected, and the basic sequence of events which
occurs during erection.
Different structures require the use of various
structural members made up of standard structural
shapes manufactured in a wide variety of shapes of
cross sections and sizes. Figure 3-1 shows many of
these various shapes. The three most common types
of structural members are the W-shape (wide flange),
the S-shape (American Standard I-beam), and the
C-shape (American Standard channel). These three
types are identified by the nominal depth, in inches,
along the web and the weight per foot of length, in
pounds.
As an example, a W 12 x 27 indicates a
W-shape (wide flange) with a web 12 inches deep and
a weight of 27 pounds per linear foot. Figure 3-2
shows the cross-sectional views of the W-, S-, and
C-shapes. The difference between the W-shape and
the S-shape is in the design of the inner surfaces of the
flange. The W-shape has parallel inner and outer
flange surfaces with a constant thickness, while the
S-shape has a slope of approximately 17’ on the inner
flange surfaces. The C-shape is similar to the S-shape
in that its inner flange surface is also sloped
approximately 17’.
Figure 3-1.—Structural shapes and designations.
Figure 3-2.—Structural shapes.
The W-SHAPE is a structural member whose
cross section forms the letter H and is the most widely
used structural member. It is designed so that its
flanges provide strength in a horizontal plane, while
the web gives strength in a vertical plane. W-shapes
are used as beams, columns, truss members, and in
other load-bearing applications.
The BEARING PILE (HP-shape) is almost
identical to the W-shape. The only difference is that
the flange thickness and web thickness of the bearing
pile are equal, whereas the W-shape has different web
and flange thicknesses.
The S-SHAPE (American Standard I-beam) is
distinguished by its cross section being shaped like the
letter I. S-shapes are used less frequently than
W-shapes since the S-shapes possess less strength and
are less adaptable than W-shapes.
The C-SHAPE (American Standard channel) has
a cross section somewhat similar to the letter C. It is
especially useful in locations where a single flat face
without outstanding flanges on one side is required.
The C-shape is not very efficient for a beam or column
when used alone. However, efficient built-up
members may be constructed of channels assembled
together with other structural shapes and connected by
rivets or welds.
An ANGLE is a structural shape whose cross
section resembles the letter L. Two types, as illustrated
in figure 3-3, are commonly used: an equal-leg angle
and an unequal-leg angle. The angle is identified by
the dimension and thickness of its legs; for example,
angle 6 inches x 4 inches x 1/2 inch. The dimension
of the legs should be obtained by measuring along the
outside of the backs of the legs. When an angle has
unequal legs, the dimension of the wider leg is given
first, as in the example just cited. The third dimension
applies to the thickness of the legs, which al ways have
equal thickness. Angles may be used in combinations
of two or four to form main members. A single angle
may also be used to connect main parts together.
Figure 3-3.—Angles.
Steel PLATE is a structural shape whose cross
section is in the form of a flat rectangle. Generally, a
main point to remember about plate is that it has a
width of greater than 8 inches and a thickness of 1/4
inch or greater.
Plates are generally used as connections between
other structural members or as component parts of
built-up structural members. Plates cut to specific
sizes may be obtained in widths ranging from 8 inches
to 120 inches or more, and in various thicknesses. The
edges of these plates may be cut by shears (sheared
plates) or be rolled square (universal mill plates).
Plates frequently are referred to by their thickness
and width in inches, as plate 1/2 inch x 24 inches. The
length in all cases is given in inches. Note in figure 3-4
that 1 cubic foot of steel weighs 490 pounds. his
weight divided by 12 gives you 40.8, which is the
weight (in pounds) of a steel plate 1 foot square and 1
inch thick The fractional portion is normally dropped
and 1-inch plate is called a 40-pound plate. In practice,
you may hear plate referred to by its approximate
weight per square foot for a specified thickness. An
example is 20-pound plate, which indicates a 1/2-inch
plate. (See figure 3-4.)
Figure 3-4.—Weight and thickness of steel plate.
The designations generally used for flat steel have
been established by the American Iron and Steel
Institute (AISI). Flat steel is designated as bar, strip,
sheet, or plate, according to the thickness of the
material, the width of the material, and (to some
extent) the rolling process to which it was subjected.
Table 3-1 shows the designations usually used for
hot-rolled carbon steels. These terms are somewhat
flexible and in some cases may overlap.
The structural shape referred to as a BAR has a
width of 8 inches or less and a thickness greater than
3/16 of an inch. The edges of bars usually are rolled
square, like universal mill plates. The dimensions are
expressed in a similar manner as that for plates; for
instance, bar 6 inches x 1/2 inch. Bars are available in
a variety of cross-sectional shapes—round,
hexagonal, octagonal, square, and flat. Three different
shapes are illustrated in figure 3-5. Both squares and
rounds are commonly used as bracing members of
light structures. Their dimensions, in inches, apply to
the side of the square or the diameter of the round.
Table 3-1.—Plate, Bar, Strip, and Sheet designation
Figure 3-5.—Bars.
Now that you have an introduction to the various
structural members used in steel construction, the best
examples of how they are used would be to develop a
theoretical building frame project that would be worked on after all the
earthwork and footings or slab have been completed.
This sequence is theoretical and may vary somewhat,
depending on the type of structure being erected.
We'll assume that all of the steel has already been
fabricated and welded and that the erection is going
to begin.
ANCHOR BOLTS
Anchor bolts (fig. 3-6) are cast into the concrete
foundation. They are designed to hold the column
bearing plates, which are the first members of a steel
frame placed into position. These anchor bolts must
be positioned very carefully so that the bearing plates
will be lined up accurately. These are usually set
using a template of the column bearing plates.
Anchor bolts can be various diameter sizes and
can be set to various depths depending on the
size of the column that it will support. Multiple
anchor bolts will be used for larger columns.
Figure 3-6.—Anchor bolts.
The column bearing plates are steel plates of
various thicknesses in which holes have been either
drilled or cut with an oxygas torch to receive the
anchor bolts (fig. 3-7). The holes should be slightly
larger than the bolts so that some lateral adjustment of
the bearing plate is possible. The angle connections,
by which the columns are attached to the bearing
plates, are bolted or welded in place according to the
size of the column, as shown in figure 3-8.
Figure 3-7.—Column bearing plate sample.
Figure 3-8.—Typical column to baseplate connections.
After the bearing plate has been placed into
position, shim packs are set under the four comers of
each bearing plate as each is installed over the anchor
bolts, as shown in figure 3-9. ‘The shim packs are 3- to
4-inch metal squares of a thickness ranging from 1 1/6
to 3/4 inch, which are used to bring all the bearing
plates to the correct level and to level each bearing
plate on its own base.
Figure 3-9.—Leveled bearing plate.
The bearing plates are first leveled individually by
adjusting the thickness of the shim packs. This
operation may be accomplished by using a 2-foot level
around the top of the bearing plate perimeter and
diagonally across the bearing plate.
Upon completion of the leveling operation, all
bearing plates must be brought either up to or down to
the grade level required by the structure being erected
All bearing plates must be lined up in all directions
with each other. This may be accomplished by using
a surveying instrument called a builder’s level. String
lines may be set up along the edges and tops of the
bearing plates by spanning the bearing plates around
the perimeter of the structure, making a grid network
of string lines connecting all the bearing plates.
After all the bearing plates have been set and
aligned, the space between the bearing plate and the
top of the concrete footing or slab must be filled with
a hard, nonshrinking, compact substance called
GROUT. (See fig. 3-9.) When the grout has hardened
the next step is the erection of the columns.
COLUMNS
Wide flange members, as nearly square in cross
section as possible, are most often used for columns.
Large diameter pipe is also used frequently (fig. 3-10),
even though pipe columns often present connecting
difficulties when you are attaching other members.
Columns may also be fabricated by welding or bolting
a number of other rolled shapes, usually angles and
plates, as shown in figure 3-11.
Figure 3-10.—Girder span on pipe columns.
Figure 3-11.—Built-up column section.
If the structure is more than one story high, it may
be necessary to splice one column member on top of
another. If this is required, column lengths should be
such that the joints or splices are 1 1/2 to 2 feet above
the second and succeeding story levels. This will
ensure that the splice connections are situated well
above the girder or beam connections so that they do
not interfere with other second story work.
Column splices are joined together by splice
plates which are bolted, riveted, or welded to the
column flanges, or in special cases, to the webs as well.
If the members are the same size, it is common practice
to butt one end directly to the other and fasten the
splice plates over the joint, as illustrated in
figure 3-12. When the column size is reduced at the
joint, a plate is used between the two ends to provide
bearing, and filler plates are used between the splice
plates and the smaller column flanges (fig. 3-13).
Figure 3-12.—Column splice with no size change.
Figure 3-13.—Column splice with change in column size.
GIRDERS
Girders are the primary horizontal members of a
steel frame structure. They span from column to
column and are usually connected on top of the
columns with CAP PLATES (bearing connections), as
shown in figure 3-14. An alternate method is the
seated connection (fig. 3-15). The girder is attached to
the flange of the column using angles, with one leg
extended along the girder flange and the other against
the column. The function of the girders is to support
the intermediate floor beams.
Figure 3-14.—Girder span on a wide flange column.
Figure 3-15.—Seated connections.
BEAMS
Beams are generally smaller than girders and are
usually connected to girders as intermediate members
or to columns. Beam connections at a column are
similar to the seated girder-to-column connection.
Beams are used generally to carry floor loads and
transfer those loads to the girders as vertical loads.
Since beams are usually not as deep as girders, there
are several alternative methods of framing one into the
other. The simplest method is to frame the beam
between the top and bottom flanges on the girder, as
shown in figure 3-16. If it is required that the top or
bottom flanges of the girders and beams be flush, it is
necessary to cut away (cope) a portion of the upper or
lower beam flange, as illustrated in figure 3-17.
Figure 3-16.—Column splice with no size change.
Figure 3-17.—Coped and blocked beam ends.
BAR JOIST
Bar joists form a lightweight, long-span system
used as floor supports and built-up roofing supports,
as shown in figure 3-18. Bar joists generally run in the
same direction as a beam and may at times eliminate
the need for beams. You will notice in figure 3-19 that
bar joists must have a bearing surface. The span is
from girder to girder. (See fig. 3-20.)
Prefabricated bar joists designed to conform to
specific load requirements are obtainable from
commercial companies.
Figure 3-18.—Clearspan bar joists (girder to girder) ready to install roof sheeting.
Figure 3-19.—Bar joists seat connection.
Figure 3-20.—Installing bar Joists girder to girder.
TRUSSES
Steel trusses are similar to bar joists in that they
serve the same purpose and look somewhat alike.
They are, however, much heavier and are fabricated
almost entirely from structural shapes, usually angles
and T-shapes. (See fig. 3-21.) Unlike bar joists,
trusses can be fabricated to conform to the shape of
almost any roof system (fig. 3-22) and are therefore
more versatile than bar joists.
Figure 3-21.—Steel truss fabricated from angle-shaped members.
Figure 3-22.—Different styles of truss shapes.
The bearing surface of a truss is normally the
column. The truss may span across the entire building
from outside column to outside column. After the
trusses have been erected, they must be secured
between the BAYS with diagonal braces (normally
round rods or light angles) on the top chord plane (fig.
3-23) and the bottom chord plane (fig. 3-24). After
these braces are installed, a sway frame is put into
place. (See fig. 3-25.)
Figure 3-23.—Diagonal braces-top chord plane.
Figure 3-24.—Diagonal braces-bottom chord plane.
Figure 3-25.—Sway frame.
PURLINS, GIRTS, AND EAVE STRUTS
Purlins are generally lightweight and
channel-shaped and are used to span roof trusses.
Purlins receive the steel or other type of decking, as
shown in figure 3-26, and are installed with the legs
of the channel facing outward or down the slope of the
roof. The purlins installed at the ridge of a gabled roof
are referred to as RIDGE STRUTS. The purlin units
are placed back to back at the ridge and tied together
with steel plates or threaded rods, as illustrated in
figure 3-27.
Figure 3-26.—Roof purlin.
Figure 3-27.—Ridge struts.
The sides of a structure are often framed with girts.
These members are attached to the columns
horizontally (fig. 3-28). The girts are also channels,
generally the same size and shape as roof purlins.
Siding material is attached directly to the girts.
Figure 3-28.—Wall girt.
Another longitudinal member similar to purlins
and girts is a cave strut. This member is attached to
the column at the point where the top chord of a truss
and the column meet at the cave of the structure. (See
fig. 3-29.)
Figure 3-29.—Eave strut.
FABRICATING PLATE AND STRUCTURAL MEMBERS
Up to this point, we have dealt with already fabricated
assemblies. In order to get to the assembly stage of a
structural project, someone needs to lay out and fabricate
steel plate and structural steel members. Steel plate is
much thicker than sheet steel and is more difficult to
work with and form into the desired shapes. In order to
fabricate properly, you'll need to have an accurate
field sketch or shop drawing of the item to be
fabricated, adequate lighting, and layout tools.
When laying out steel plate, you should have the
following tools: an adequate scale, such as a
combination square with a square head, an accurate
protractor, a set of dividers, a prick punch, a center
punch, and a ball peen hammer.
When layout marks are made on steel, you must
use a wire brush to clean the areas and remove the residue
or loose mill scale with a brush or rag. Then paint the surface with a
colored marking compound. Aerosol spray is very
good because it allows the paint to fall only in the areas
to be laid out and also because it produces a thin coat
of paint that will not chip or peel off when lines are
being scribed.
When appropriate, the layout lines can be drawn
on steel with a soapstone marker or a similar device.
However, remember that the markings of many of
these drawing devices can burn off under an oxy-gas
flame or be blown away by the force of oxygen
from the cutting torch. These conditions are
undesirable and can ruin an entire fabrication job. If
using soapstone or a similar marker is your only
option, be sure to use a punch and a ball peen hammer
to make marks along the cut lines. By “connecting the
dots,” you can ensure accuracy. Punch marks are normally
placed around 1/4" or 6 mm apart to insure cutting accuracy.
Plan material usage before starting the layout on
a plate. An example of proper plate layout and material
usage is shown in figure 3-30. Observe the material
used for a cooling box. It will take up slightly more
than half of the plate. The rest of the material can then
be used for another job. This is only one example, but
the idea is to conserve materials. An example of poor
layout is shown in figure 3-31. The entire plate is used
up for this one product, wasting material, increasing
the cost and layout time of the job.
Figure 3-30.—Proper plate steel cooling box layout.
Figure 3-31.—Improper plate steel cooling box layout.
The layout person must have a straight line or
straightedge that he or she refers all measurements to.
This straightedge or line can be one edge of the work
that has been finished straight; or it can be an outside
straight line fastened to the work, such as a
straightedge clamped to the work. A good technique on longer
pieces is to snap a chalk line and then use punch marks.
When the layout is complete, the work should be
checked for accuracy, ensuring all the parts are in the
layout and the measurements are correct. After
determining that the layout is accurate, the layout person
should center punch all cutting lines. This ensures
accurate cutting with either a torch or shears. The work
can be checked after cutting because each piece will have
one half of the center punch marks on the edge of the
material. Remember, always cut with the kerf of the
torch on the outside edge of the cutting lines.
LAYOUT OF STRUCTURAL SHAPES
Structural shapes are slightly more difficult to lay
out than plate. This is because the layout lines may not
be in view of the layout person at all times. Also, the
reference line may not always be in view.
Steel beams are usually fabricated to fit up to
another beam. Coping and slotting are required to
accomplish this. Figure 3-32 shows two W 10 x 39
beams being fitted up. Beam A is intersecting beam B
at the center. Coping is required so beam A will butt
up to the web of beam B; the connecting angles can be
welded to the web, and the flanges can be welded
together.
Figure 3-32.—Fabrication and fit-up for joining two beams of the same size.
A cut 1 1/8 inches (2.8 cm) long at 45 degrees at
the end of the flange cope will allow the web to fit up
under the flange of beam B and also allow for the fillet.
The size of the cope is determined by dividing the
flange width of the receiving beam in half and then
subtracting one half of the thickness of the web plus
1/16 inch. This determines how far back on beam A
the cope should be cut.
When two beams of different sizes are connected,
the layout on the intersecting beam is determined by
whether it is larger or smaller than the intersected
beam. In the case shown in figure 3-33, the
intersecting beam is smaller; therefore, only one
flange is coped to fit the other. The top flanges will be
flush. Note that the angles on this connection are to be
bolted, rather than welded.
Figure 3-33.—Typical framed construction, top flange flush.
CONNECTION ANGLE LAYOUT
A very common connection with framed
construction is the connection angle. The legs of the
angles used as connections are specified according to
the surface to which they are to be connected. The legs
that attach to the intersecting steel to make the
connections are termed web legs. The legs of the
angles that attach to the supporting or intersected steel
beam are termed outstanding legs. The lines in which
holes in the angle legs are placed are termed gauge
lines. The distances between gauge lines and known
edges are termed gauges. An example of a completed
connection is shown in figure 3-34. The various terms
and the constant dimensions for a standard connection
angle are shown in figure 3-35.
Figure 3-34.—gauge lines.
Figure 3-35.—Standard layout for connection angle using 4-inch by 4-inch angle.
The distance from the heel of the angle to the first
gauge line on the web leg is termed the web leg gauge.
This dimension has been standardized at 2 1/4 inches
(5.6 cm). This dimension is constant and does not vary.
The distance from the heel of the angle to the first
gauge line on the outstanding leg is called the
outstanding leg gauge. This dimension varies as the
thickness of the member, or beam, varies. This
variation is necessary to maintain a constant
5 1/2-inch-spread dimension on the angle connection.
The outstanding leg gauge dimension can be
determined in either one of the following two ways:
1. Subtract the web thickness from 5 1/2 inches
(13.8 cm) and divide by 2.
2. Subtract 1/2 of the web thickness from 2 3/4
inches.
The distance between holes on any gauge line is
called pitch. This dimension has been standardized at
3 inches (7.5 cm). The end distance is equal to one half of the
remainder left after subtracting the total of all pitch
spaces from the length of the angle. By common
practice, the angle length that is selected should give
a 1 1/4-inch (3-cm) end distance.
All layout and fabrication procedures are not
covered in this article. Some examples are shown in
figure 3-36. Notice that the layout and fabrication area
has a table designed to allow for layout, cutting, and
welding with minimum movement of the structural
members. Material is stored on wooden blocks also
known as dunnage to protect it from excess ground
moisture. This setup is typical in most fabrication
shops when room allows.
The table holds two columns being fabricated out
of beams with baseplates and cap plates. Angle clips
for seated connections (fig. 3-37) should be installed
before erection.
Figure 3-36.—Prefab table and steel storage.
Figure 3-37.—Seated connection.
CUTTING AND SPLICING BEAMS
At times, the fabricator will be required to split a
beam to make a tee shape from an I shape. This is done
by splitting through the web. The release of internal
stresses locked up in the beams during the
manufacturer’s rolling process causes the split parts to
bend or warp as the beams are being cut unless the
splitting process is carefully controlled.
The recommended procedure for cutting and
splitting a beam is first to cut the beam to the desired
length and then proceed as follows:
1. Make splitting cuts about 2 feet (60 cm) long,
leaving 2 inches (5 cm) of undisturbed metal between
all cuts and at the end of the beam (fig. 3-38). As the cut
is made, cool the steel behind the torch with a water
spray or wet burlap.
2. After splitting cuts have been made and the
beam cooled, cut through the metal between the cuts,
starting at the center of the beam and working toward
the ends, following the order shown in figure 3-38.
Figure 3-38.—Cutting order for splitting a beam.
The procedure for splitting a beam also works very
well when splitting plate and is recommended when
making bars from plate. Multiple cuts from plate can
be made by staggering the splitting procedure before
cutting the space between slits. If this procedure is
used, ensure that the entire plate has cooled so that the
bars will not warp or bend.
TEMPLATES
When a part must be produced in quantity, a
template is made first and the job laid out from the
template. A template is any pattern made from sheet
metal, regular template paper, wood, or other suitable
material, which is used as a guide for the work to be
done. A template can be the exact size and shape of
the corresponding piece, as shown in figure 3-39,
views 1 and 2, or it may cover only the portions of the
piece that contain holes or cuts, as shown in views 3
and 4. When holes, cuts, and bends are to be made in
a finished piece, pilot holes, punch marks, and notches
in the template should correspond exactly to the
desired location in the finished piece. Templates for
short members and plates are made of template paper
of the same size as the piece to be fabricated.
Templates for angles are folded longitudinal] y, along
the line of the heel of the angle (fig. 3-39, view 3).
Figure 3-39.—Paper and combination templates.
Accurate measurements in making templates
should be given careful attention. Where a number of
parts are to be produced from a template, the use of
inaccurate measurements in making the template
obviously would mean that all parts produced from it
will also be wrong. Template paper is a heavy cardboard material with
a waxed surface. It is well adapted to scribe and
divider marks. A combination of wood and template
paper is sometimes used to make templates. The use
of wood or metal is usually the best choice for
templates that will be used many times.
For long members, such as beams, columns, and
truss members, templates cover only the connections.
These templates may be joined by a wooden strip to
ensure accurate spacing (fig. 3-39, views 1 and 2).
They may also be handled separately with the template
for each connection being clamped to the member
after spacing, aligning, and measuring.
In making templates, the same layout tools
discussed earlier in this chapter are used. The only
exception is that for marking lines, a pencil or
Patternmaker’s knife is used. When punching holes in
a template, keep in mind that the purpose of the holes
is to specify location, not size. Therefore, a punch of
a single diameter can be used for all holes. Holes and
cuts are made prominent by marking with paint.
Each template is marked with the assembly mark
of the piece it is to be used with, the description of the
material, and the item number of the stock material to
be used in making the piece.
In laying out from a template, it is important that
the template be clamped to the material in the exact
position. Holes are center punched directly through
the holes in the template (fig. 3-40), and all cuts are
marked. After the template is removed, the marks for
cuts are made permanent by rows of renter punch
marks.
Figure 3-40.—Use of template in laying out a steel channel.
It is important that each member or individual
piece of material be given identifying marks to
correspond with marks shown on the detail drawing
(fig. 3-41).
Figure 3-41.—Erection and assembly marks.
The ERECTION MARK of a member is used to
identify and locate it for erection. It is painted on the
completed member at the left end, as shown on the
detail drawing, and in a position so that it will be right
side up when the member is right side up in the
finished structure.
An ASSEMBLY MARK is painted on each piece
on completion of its layout so that the piece can be
identified during fabrication and fit up properly with other
pieces to form a finished member.
JOINING ASSEMBLIES
Structural assemblies are joined by either bolting
together or welding together. Depending on the design,
bolting can be with either standard nuts and bolts or
torque control nuts and bolts. Torque control nuts,
bolts, and washers are specially designed with a
small piece on the end of the bolt that breaks off
when the proper torque pressure has been achieved.
Torque control bolts are usually used to control
load bearing connections in a structure.
Most welding of structural components and assemblies
is accomplished with one of three different processes:
1. SAW (Sub Arc Welding)
2. SMAW (Shielded Metal Arc Welding)
3. FCAW (Flux Core Arc Welding)
Other welding processes are used to a lesser extent,
but the above three account for the majority of
structural welds. Sub arc welding is done mostly
at the fabrication stage in shops. Flux core and
shielded metal arc welding are accomplished both
in the shop and in the field.
Although this article is not "all inclusive", it
should give the reader a pretty good overview of how
many buildings are constructed, what some of the various
parts are, and how they connect to each other along
with some standard layout and fabrication methods.