Page 307 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

292 Chapter Four

service load but also below the ultimate strength of the connection. To
meet this criterion, Astaneh-Asl (1995) recommends that the nominal
slip resistance (F ) be such that
slippage

1.25F service # F slippage # 0.80F ultimate
where F corresponds to the nominal slip strength of the bolt group
service
and F corresponds to the nominal shear strength of the bolts.
ultimate
5. Web connection design: The design of the web connection is usu-
ally made without much regard to the contribution of this part of the
connection to the flexural strength of the joint unless the flange con-
nections carry less than 70% of the total moment (AISC, 1992). It is
clear from the performance of MRF’s during the Northridge earth-
quake that careful attention should be paid to ensure that the web
connection is detailed to provide rotational ductility and strength that
are compatible with the action of the flanges. Astaneh-Asl (1995) sug-
gests that the shear plates be designed to develop the plastic moment
strength of the web:

h t s0.6F d . h t s0.6F d
yw
p p
yp
gw gw
2
h p t F yp . h t F yw
gw gw
p
where h and t are the depth and thickness, F is the yield strength, and
y
the subscripts p and gw refer to the shear plate and the beam web,
respectively. Here again, allowances should be made for the steel over-
strength (say R 1.1 to 15). Failure modes to be avoided include bolt
y
shear, block shear, net area fractures, and weld fractures.
Design Example 4.1: Design a full-strength connection between a W 21 62
girder and a W 14 120 column. Both sections are A572 GR 50. Design for
wind loads assuming the analysis shows a maximum moment (M ) of 425 kip-ft
u
(5100 kip-in) and a maximum shear (V ) of 75 kips. The service moment (M )
u serv
is 140 kip-ft (1680 kip-in). Assume A325X 7/8-in-diameter bolts.
1. Check local buckling:
Flange:
b E
a b 5 6.1 # 0.38 5 9.2 ok
t BF y

Web:

h E
a b 5 46.9 # 3.76 5 90.6 ok
t w BF y

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