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When working on a steel
construction project, the
Structural Engineer of
Record (SER) can create
an economical structure
that is fabricator and erector friendly, especially
with good communication and
teamwork on the project design and construction
teams.
If the fabricator designs the connections,
sealed calculations usually need to
be submitted to the SER for review. Also,
the load criteria need to be given on the
contract documents. For moment and axially
loaded connections, the actual design
load or a percentage of the
member’s capacity is given. For shear
connections, one of three methods (or a
combination) is used:
➜ The actual beam shear loads are given.
➜ Abeam shear-load schedule for different
beam depths are given.
➜ The SER specifies that the shear load
will be determined based on a percentage
of the beam’s uniform distributive
load capacity (UDL).
If a beam shear-load schedule or a
percentage of UDL is given, the actual
criteria specified by the SER should satisfy
the required loading. However, the
criteria should not be so conservative as
to unnecessarily create the need for excessive
typical shear connections (more
than two vertical rows of bolts or more
than full-depth connections).
For the most economical structure, it
is preferred that shear loads be given on
drawings for every beam. There are also
conditions where a beam shear-load
schedule or the UDL method do not
apply and actual loads should be given:
➜ At beams with concentrated loads
near the beam end.
➜ At beams sized for serviceability requirements
rather than strength requirements.
➜ At infill beams that support a relatively
small area.
➜ At beams with axial load.
At relatively short beams, the UDL
method usually gives overly conservative
shear loads, and an upper-limit shear
load or the actual beam shear load
should be given.
Below are some recommendations for
cost-effective connection design that also
could reduce problems in the field:
1. At bolted flange-plated connections,
the flange plate should not be the
same width as the beam flange.
Allow at least a ½” difference on each side
of the flange plate at bolted flange-plated
connections. If bolt holes misalign in the
field, there will be a sufficient shelf dimension
to place longitudinal fillet welds
to compensate for the missing bolts.
2. Use oversized holes in beam moment
and brace connections.
At flange-plated moment connections or
brace connections with slip-critical bolts,
oversized bolt holes are often preferred
over standard bolt holes. Although standard
holes give a greater bolt capacity,
oversized holes permit more erection tolerance
and reduce field problems. Typically,
oversized holes are used in the
detail material and standard holes in the
main member.
3. Group similar connections rather than
have several different connections.
Connections on a project should be as
uniform as possible to save fabrication
time and reduce the possibility of errors.
4. Limit the number of bolt diameters to
one size (a maximum of three sizes if
necessary).
This reduces field errors as well as fabrication
errors with drill lines that have
manually changed spindles. Some fabricators/
erectors keep at least a ¼” difference
between bolt sizes to prevent uncertainty.
5. Avoid different grade bolts with the
same diameter.
6. Use bolted connections instead of
field-welded connections.
Bolted connections are quicker to erect
and less costly. Welded connection delays
result from the absence of a qualified
welder or welding platforms, or cold
windy weather.
7. Try to use fillet welds instead of partial-
penetration or full-penetration
welds.
Fillet welds are less expensive, since no
base-metal preparation is needed. Also,
partial- and full-penetration welds usually
require more weld metal and inspection.
8. Limit the maximum fillet weld size to
5/16” (especially in the field).
This is the maximum-size weld that can
be completed in a single pass using the
shielded-metal arc-welding (SMAW)
process. Smaller, longer welds are preferred
over larger, shorter welds.
9. Avoid overhead welding.
The preferred welding positions are flat
and horizontal. Overhead welding is difficult,
costly and generally yields lowerquality
welds. For single-pass SMAW fillet
welds, it can take four times as long as
welding in the flat or horizontal position.
10. Use full-penetration welds only
when necessary.
Full-penetration welds cost more than
partial-penetration or fillet welds due to
increased material preparation, testing
requirements, weld-metal volume and
material distortion. Use fillet welds (pro-
May 2004 • Modern Steel Construction
30 Good Rules
for Connection Design
By Carol Drucker, S.E.
Practical tips for designing economical, fabricator- and erector-friendly steel connections
vided that the fabricator does not determine
them excessively large) or partialpenetration
welds when joint strength is
adequate for the applied load. Full-penetration
welds at HSS members are difficult
due to the need for backing bars.
11. Consider finishing to bear.
For connections with high compressive
loads, it could be more economical to finish
the steel to bear and provide AISC’s
minimum-required weld size instead of
transferring the compressive force
through large fillet or groove welds.
When steel is to be finished to bear, it
must be indicated on the connection detail.
The detail also should call for the
beam flanges to be square to the beam
web. In detailing, stiffeners might need to
be longer than d-2tf for beam overrun in
depth and variation in beam-flange
thickness. Per AISC Specification Section
M, gaps not exceeding 1/16” are permitted
in bearing connections.
12. Avoid excessive connections.
Connections should be designed to actual
load requirements. The SER should
not specify that connections be designed
for the members’ full capacity if not necessary.
Excessive connections increase
construction cost and the possibility of
problems in the field. Over-welding can
damage the steel.
13. Specify only prequalified welds.
The welding procedure specification
(WPS) for a weld not American Welding
Society (AWS) prequalified must be
tested. To avoid the cost, time and confusion
of qualification, use only prequalified
welds.
14. Minimize weld volume at full- and
partial-penetration welds.
The weld configuration with the least weld
volume is the most economical. For weld
configurations with double-sided preparation,
consider the additional cost of material
preparation, since it could offset the
cost savings of less weld metal. For fullpenetration
welds, it is economical to prep
one side of plates with a thickness less than
1” and to prep both sides of plates with a
thickness greater than or equal to 1”.
15. Provide proper clearance for
bolted and welded connections.
AISC’s LRFD Manual of Steel Construction,
3rd Edition, Parts 7 and 8, give the necessary
clearances for bolted and welded
connections.
16. Specify slip-critical bolts only
when necessary.
Slip-critical bolts are not always needed at
moment and brace connections, and bearing
bolts might be acceptable in standard
holes. The RCSC (Research Council on
Structural Connections) Specification,
Section 4.3 gives criteria for slip-critical
joints, which are more costly than bearing
joints due to additional installation, inspection
and faying-surface preparation.
Also, more or larger bolts are needed for
reduced bolt strength. In certain conditions,
fabricators/erectors might prefer
slip-critical bolts for oversized holes and
greater erection tolerance.
If slip-critical joints and bolts are
needed, the steel detailer must indicate
them on the erection and shop drawings.
The detailer should indicate masking requirements
in the bolt-hole area to keep
the faying surface free of coatings from
inadvertent overspray of unqualified
paint.
17. Allow bearing bolts at the shear
connection of flange-welded moment
connected beams.
At directly welded moment connections
or flange-plated moment connections
welded to the supported beam, bearing
bolts can be used in the beam-web shear
connection. Since the flange weld and the
web bolts are not on the same faying surface,
the web bolts do not need to be slipcritical.
(See AISC’s LRFD Specification
Commentary, Section J1.9). Also, since
the web bolts will be installed prior to the
completion of the flange weld, the web
bolts should be in bearing.
18. Limit the maximum bolt diameter
to 11/8” diameter.
Bolts with diameters greater than 11/8”
are difficult to tighten, not commonly
used, and costly. ASTM A490 bolts
greater than 1” diameter have a disadvantage
in slip-critical connections with
oversized or slotted holes. Hardened
washers with a 5/16” minimum thickness
(standard washers are 5/32” thick) are required
to cover oversized and short-slotted
holes in outer plies. See RCSC
Specification Section 6.2.
19. Avoid slotted holes in plates
thicker than the bolt diameter.
Slots in thick plates are hard to punch
and must be flame-cut, which is difficult
and costly. Standard holes or oversized
Modern Steel Construction • May 2004
Use shear plate connections at beam-to-column flange-plated moment connections (see tip 20).
holes are preferred.
20. Use shear plate connections at
beam-to-column flange-plated
moment connections.
If flange plates need to be welded to a
column flange, a shear-plate connection
is preferred. Since the column needs to be
positioned in the shop for the flangeplate
welds, the shear plate can be readily
welded.
At fully restrained moment connections,
a typical shear-plate connection
can be designed for shear only (and eccentricity
in the shear connection can be
ignored). The joint rotation is considered
resisted by the flange connections.
21. Use double-angle connections at
directly welded beam-to-column
moment connections.
To avoid double-cutting the beam, double-
angle connections (bolted to the column)
are preferred over shear-plate
connections at directly welded moment
connections. At directly welded moment
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