Page 278 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.58

CRITERIA FOR BUILDING DESIGN

5.58 CHAPTER FIVE

2. Stiffener Requirements for Concentrated Forces. Stiffeners required to resist tensile concen-
trated forces must be designed as tension members and welded to the loaded flange and the web. Size
the flange welds for the difference between the required strength and the applicable available limit
state strength. Size the web welds to transfer to the web the algebraic difference in tension force at
the ends of the stiffener.
Stiffeners required to resist compressive concentrated forces must be designed in accordance with
the requirements for compression elements in Art. 5.9.9 and the dimensional requirements in Art.
5.4.3, must either bear on or be welded to the loaded flange, and must be welded to the web. The
welds to the flange must be sized for the difference between the required strength and the applicable
available limit state strength. The weld to the web must be sized to transfer to the web the algebraic
difference in compression force at the ends of the stiffener. For fitted bearing stiffeners, the bearing
strength given in Art. 5.9.12 applies.
Transverse full-depth bearing stiffeners for compressive forces applied to a beam or plate girder
flange must be designed as axially compressed members (columns) in accordance with the require-
ments for compression elements in Art. 5.9.9 and the dimensional requirements in Art. 5.4.3.
Determine member properties using an effective length of 0.75h and a cross section composed of two
stiffeners and a strip of the web having a width of 25t w (at interior stiffeners) or 12t w (at the ends of
members). The weld connecting full-depth bearing stiffeners to the web should be sized to transmit
the difference in compressive force at each of the stiffeners to the web.
Transverse and diagonal stiffeners must also comply with the following:
• The width of each stiffener plus one-half the thickness of the column web must not be less than
one-third of the width of the flange or moment connection plate delivering the concentrated force.
• The thickness of a stiffener must not be less than one-half the thickness of the flange or moment
connection plate delivering the concentrated load, and greater than or equal to the width divided
by 15.
• Transverse stiffeners must extend a minimum of one-half the depth of the member, except that full-
depth stiffeners are required when used to resist web local buckling and at unframed ends.

3. Doubler-Plate Requirements for Concentrated Forces. Size the doubler plate to provide the
additional material necessary to equal or exceed strength requirements. Weld the doubler plate to
develop the proportion of the total force transmitted to the doubler plate. Doubler plates required
for tension strength must be designed in accordance with the requirements for tension members
(Art. 5.3). Doubler plates required for compression strength must be designed in accordance with the
requirements for compression members (Art. 5.4). Doubler plates required for shear strength must
be designed in accordance with the requirements for members in shear (Art. 5.6).

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