Page 108 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.40

CONNECTIONS

3.40 CHAPTER THREE

Tension. Either tension yielding or fracture can govern the strength of a connecting element
subjected to tension. The design strength for yielding in the gross section is
(3.21)
φR n =φF y A g
and the design strength for fracture in the net section is
(3.22)
φR n =φF u A n
where φ= 0.90 for yielding or 0.75 for fracture
F y = specified minimum yield stress of connecting element, ksi
F u = specified minimum tensile strength of connecting element, ksi
A g = gross area of the connecting element, in 2
A n = net area of the connecting element, in 2
In some cases the entire gross or net areas of a connecting element cannot be considered effective.
This is the case for a brace attaching to a large gusset, where the effective gross area is based on the
Whitmore section. Also, for connecting elements, such as angles, where only one leg of the angle is
connected, a shear lag factor must be included into the calculation of an effective net area.
Shear. Either shear yielding or fracture can govern the strength of a connecting element subjected
to shear. The design strength for shear yielding in the gross section is
(3.23)
φR n =φ0.6F y A g
and the design strength for fracture in the net section is
(3.24)
φR n =φ0.6F u A n
where φ= 0.90 for yielding or 0.75 for fracture and other terms are as given above. Due to the resis-
tance provided by the flange, net shear fracture will govern the capacity of flanged members only
when both flanges are coped.

Bending. Either tension yielding or fracture in the tension zone can govern the strength of a con-
necting element subjected to bending (flexure). The design strength for yielding (plastic moment) in
the gross section is
(3.25)
φR n =φF y Z g
and the design strength for fracture in the net section can be taken as
(3.26)
φR n =φF u Z n
where φ= 0.90 for yielding or 0.75 for fracture
Z g = gross plastic section modulus of the connecting element
Z n = net plastic section modulus of the connecting element
For a plate with equal edge distance top and bottom and constant bolt spacing, the net plastic sec-
tion modulus can be calculated as


Z = Z 1 − d  (3.27)
h

b 
g
n
where d h = hole diameter
b = bolt spacing
This is an exact result for connections with an even number of rows and a slightly conservative estimate
for those with an odd number of rows.

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