Page 259 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.39

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.39

5.9 DESIGN OF CONNECTIONS

The required strength of connections should be determined by structural analysis for the specified
design loads, consistent with the type of construction specified. The design strength φR n and the
allowable strength R n /Ω for the connections can be determined from the provisions of the AISC
Specification. Design for static loads is summarized in this article. For design of connections sub-
jected to fatigue, see App. 3 of the AISC Specification. For design of HSS connections, see Chap. K
of the AISC Specification. Also, see Chap. 3 for additional information and examples.

5.9.1 General Provisions for Connections
As indicated in Art. 5.1.4, connections are classified for design purposes as either simple connec-
tions or moment connections. The details for simple connections must be designed to be flexible
and accommodate end rotations of simple beams. The AISC Specification allows them to be pro-
portioned for the reaction shears only, and self-limiting inelastic deformation in the connection ele-
ments is permitted. For moment connections, the design must consider the combined effect of forces
resulting from both moment and shear.
Compression members such as columns or chords of trusses are often designed with joints that
transmit the compression in bearing. AISC gives the following rules:

(a) When columns bear on bearing plates or are finished to bear at splices, there shall be sufficient
connectors to hold all parts securely in place.
(b) When compression members other than columns are finished to bear, the splice material and its
connectors shall be arranged to hold all parts in line and shall be proportioned for either (i) or (ii), below.
It is permissible to use the less severe of the two conditions:
(i) An axial tensile force of 50 percent of the required compression strength of the member; or
(ii) The moment and shear resulting from a transverse load equal to 2 percent of the required com-
pression strength of the member. The transverse load shall be applied at the location of the splice exclu-
sive of other loads that act on the member. The member shall be taken as pinned for the determination of
the shears and moments at the splice.
Splices in heavy sections, defined as rolled sections with a flange thickness greater than 2 in (50 mm)
or built-up sections with plates thicker than 2 in (50 mm), must meet additional requirements. When
tensile forces due to applied tension or flexure are transmitted through splices in heavy sections, by
complete-joint-penetration (CJP) groove welds, the material must provide a Charpy V-notch impact
toughness of 20 ft⋅lb (27 J) at + 70°F (+21°C). Also, beam copes and weld access holes must be
shaped to specified criteria and thermal cut surfaces must be ground to bright metal and inspected by
magnetic particle or dye-penetrant methods. These requirements are not applicable to splices of
plates of built-up shapes that are welded prior to assembling the shape. Also, as an alternative to the
requirements, consider splices using partial-joint-penetration (PJP) groove welds for the flanges and
fillet-welded web splice plates, or using bolts for some or all of the splice.
Eccentricity, which affects the distribution of resisting forces, must be considered in the design
of connections for groups of welds or bolts at the ends of members that transmit axial force, unless
the center of gravity of the group coincides with the center of gravity of the member. However, such
eccentricity need not be considered for end connections of members such as statically loaded single
or double angles.
Bolts used in combination with welds cannot be designed to share the load with the welds
except for the following. Shear connections with bolts installed in standard holes or in short slots
transverse to the direction of the load may share the load with longitudinally loaded fillet welds, but
the available strength of the bolts must not be taken as greater than 50% of the available strength of
bearing-type bolts (see Art. 5.9.8). This exception applies to both high-strength bolts and A307 bolts.
Also, in alterations or rehab work, existing rivets and high-strength bolts tightened to the require-
ments for slip-critical connections may be used to carry existing loads, and the welding used to pro-
vide the additional required strength.

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.