Page 296 - Handbook of Structural Steel Connection Design and Details

Partially Restrained Connections

Partially Restrained Connections 281

Both the absolute and relative rotation capacities need to take into
account any strength degradation that may occur as a result of local
buckling or slip, particularly under cyclic loads. The behavior of the
connections shown by the solid (SMF ND), dashed (SMF D), and dot-
ted (IMF D) lines in Fig. 4.4 can lead to significant differences in
frame behavior, especially with respect to strength and stability.
Finally, it should be emphasized that the limits discussed above, with
the exception of the interstory drift and 0.8M ones appearing in
p, beam
ASIC 360 (2005), are based purely on the opinions of the author.
Limits for ductility criteria, such as those described previously, are
only now being developed, but this issue is highlighted here to remind
designers that analysis assumptions (unlimited rotational ductility, in
general) must be consistent with the detailing of the connection. This
is true for both PR and FR frames.

4.2.4 Derivation of M- curves

As noted earlier, M- curves have typically been derived from exper-
iments. Many of these tests have been collected into databases (Ang
and Morris 1984, Goverdhan, 1984, Nethercot, 1985, Kishi and
Chen, 1986, Chan and Chiu, 2000, for example). Based on these
databases, equations for the complete M- curves for different types
of connections have been proposed. However, numerous important
variables, such as the actual yield strength of the materials and the
torque in the bolts, are generally poorly documented or missing for
many of these tests. Thus many of the M- curves and equations
available from these databases cannot be considered as reliable. In
addition, care should be exercised when utilizing tabulated moment-
rotation curves not to extrapolate to sizes or conditions beyond those
used to develop the database since other failure modes may control
(ASCE, 1997).
Two approaches have recently become practical alternatives and/or
complements to experimental testing in developing M- curves. The
first alternative is a detailed, nonlinear finite-element analysis of the
connection. While time-consuming because of the extensive paramet-
ric studies required to derive reliable M- curves, this approach has
gone from a pure research tool to an advanced design office tool in
just a few years thanks to the tremendous gains in computational
power available in new desktop workstations.
The other approach is the one proposed by the Eurocodes and com-
monly labeled the “component approach.” In this case each deforma-
tion mechanism in a joint is identified and individually quantified
through a series of small component tests. These tests are carefully
designed to measure one deformation component at the time. Each of
these components is then represented by a spring with either linear or

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com)
Copyright © 2009 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.