Page 319 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

304 Chapter Four

The tensile strength of the bolts: This is influenced primarily by the
prying action.
The shear strength of the bolts: It is difficult to fit more than 8 to
10 bolts in the stem of a conventional T (cut form a W shape) and
thus large bolts may be needed.

Each of these failure modes must be checked individually and the
lowest strength taken as the controlling value. Guidelines for these
calculations are given in the AISC Manual (AISC, 1993), textbooks
(see for example, pp. 848–856 of Salmon and Johnson, 1996), and in
the standard references (Kulak et al., 1987). An excellent review of
the design, including some of the numerical problems that can be
encountered is given by Thorton (1985). In this chapter, Example 4.3
is based on the work of Swanson and Leon (2000, 2001), while
Example 4.4 is based on unpublished work by Swanson, Rassati and
Leon for AISC 358.
The effect of reversed cyclic loading on these connections is to pro-
gressively decrease the tension in the bolts to the column flange.
Because of prying action, the stress range in these bolts is probably
significantly larger than that calculated based on the simplified mod-
els used for design. This can result in either low-cycle fatigue failures
or in fracture of the bolt due to excessive elongation.

Design Example 4.3: A rigid connection is to be designed to transfer a factored
moment of 260.6 kip-ft and a factored shear of 112 kip from a W 21 57 beam
to the flange of a W 14 82 column. The connection consists of T sections for
moment transfer and web angles for shear transfer. All materials are A36 steel.
Bolts are to be 1-in A325-N bolts. Seismic design is not required.
1. If all bending moment is carried by the tees, the force of the internal couple is

260.6 3 12
M u
F > 5 5 148.4 kips
d b 21.06
2. Determine the minimum number of bolts (N) required to carry the tensile
force to the column flange. Ignore the prying forces for now and check later.
R n 5 F t A b 5 s0.75ds90ds0.785d 5 53.0 kips/bolt
N 148.4/53 2.8 say 4 bolts
Note that because prying forces can be large in this type of connection, it is best
to have a very conservative number of bolts to the column flange. This check is
used here mostly to ensure that a reasonable number of bolts are needed (that
is 4 to 8 bolts rather than more, which would be hard to accommodate).
3. Determine the number of bolts (M) required to transmit the forces from the
tee to the beam flanges through shear (bolts are in single shear):
R n 5 0.75F v A b 5 0.75s48ds0.7856d 5 28.3 kips/bolt

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