Page 274 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.54

CRITERIA FOR BUILDING DESIGN

5.54 CHAPTER FIVE

If d > 25 in (635 mm),

60.( F −13) l d
R = y (5.159a)
n
20
30 2.( F − 90) l d
SI: R = y (5.159b)
n
20
where d = diameter, in (mm)
l = length of bearing, in (mm)
For bearing strength in bolt holes, see Art. 5.9.8.

5.9.13 Bearing on Concrete
The available bearing strength (design bearing strength φP p and allowable bearing strength P p /Ω) for
column bases on concrete is determined as follows for the limit state of concrete crushing. Use φ c =
0.60 (LRFD) and Ω= 2.50 (ASD).
When the base bears on the full area of a concrete support, the nominal bearing strength, P p , is

(5.160)
P p = 0.85f c ′A 1
When the base bears on less than the full area of a concrete support, the nominal bearing strength is

.
P = 085 f A ′ 1 A A ≤17 f A ′ 1 (5.161)
/
.
1
2
c
p
c
2
2
2
where A 1 = area of steel concentrically bearing on a concrete support, in (mm ) and A = maximum
area of the portion of the supporting surface geometrically similar to and concentric with the loaded
2
2
area, in (mm ). Also, A 2 ≤ 4A 1 .
5.9.14 Design of Flanges and Webs for Concentrated Forces
This article addresses the design of single- and double-concentrated forces acting normal to the
flange of wide flange sections and similar built-up shapes. A single concentrated force can be either
tensile, such as from a hanger, or compressive, such as from an end reaction. Double-concentrated
forces treated are one tensile and one compressive, oriented so as to form a couple on the same side
of the member, such as the forces applied to a column flange by a beam in a moment connection.
When the required strength exceeds the available strength as determined for each limit state in
this article, stiffeners and/or doublers (plates welded to and parallel with webs to increase resistance
to concentrated forces) must be provided and designed for the difference between the required
strength and the available strength. Stiffeners and doublers must also meet certain additional design
requirements presented in Art. 5.9.15.
Design for various limit states is treated in the following. Local flange bending applies only for
tensile forces, local web yielding applies for both tensile and compressive forces, and the other limit
states apply only to compressive forces.
1. Local Flange Bending. This limit state applies to tensile single-concentrated forces and the ten-
sile component of double-concentrated forces.
The available strength (design strength φR n and allowable strength R n /Ω) is determined for the
limit state of local flange bending from
2
R n = 6.25t f F yf (5.162)
φ= 0.90 (LRFD) Ω= 1.67 (ASD)

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