where; Pn is calculated using AISC LRFD 2nd ed. column
load tables as follows;
From the tables with KL = 1.0(25' = 25'(7.62m)
)
k
k
Pn = 29 /0.85 = 34.1 (151.7KN)
Check DCR ratio in compression;
Q UD 30.4 k
=
= 0.71 < 0.8 = m
O.K.
QCE 42.6k
Use TS 4.5x4.5x1/4 (TS 114.3mmX114.3mmX6.4mm)
e.
Design connections.
General;
Governing design loads can be from either of ground motions A or B. Ground motion A consists of two
thirds of the Maximum Considered Earthquake (MCE), includes R values, and was used in performance
objective 1A. Ground motion B consists of three-quarters of the MCE, does not include R-values, and was
used in performance objective 3B. Further, for force controlled components, the seismic load from ground
motion B is divided by the modification factors C1, C2, C3, and J to restore it to a force-controlled action.
However, some elements of the connections may derive their design loads from the expected strength of
other connection elements. For example, panel zone shear used to determine the need for doubler plates is
limited by expected strength of the beams framing to the column flanges, and the design load for continuity
plates is taken from the expected strength of the beam flanges. Additionally, brace frame connections may
be designed for the expected strength of the brace.
Two example connection designs will be shown; a moment connection and a braced frame connection.
Both connections are from the low roof portion of the building.
Low Roof;
Transverse direction;
Moment frames;
In designing the main elements of the moment frame (i.e., the beams and columns) most of the
requirements of the AISC seismic provisions for moment connections had been met. What remains is to
determine the need for doubler plates, the need for continuity plates, and the design of the bolted gravity
load connection at the beam web.
Determine if doubler plates are required;
Determine Demand;
Note: Loading from performance objective 1A including the structural overstrength factor ( Ω o = 3 ) could
have been used to determine a smaller demand ` u' However, it is more convenient to apply the expected
R .
∑R
strength requirement of 0.8 times
as follows;
yMp
∑R
0.8
y Mp
Ru =
(per AISC seismic provisions dated April 15, 1997)
d b + d haunch - t f
where; Ry = 1.5 (for ASTM A36)
Mp = ZxFy = 43.24-in3(36ksi) = 1,557in-kips (175.9KN-m)
db = 13.91" (353.3mm)
H4-50
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