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Section 2
2-17
D = Maximum local deflection for members
1 2 and 3.
D
1
23
4
1
23
EXAMPLE : PARAMETERS
DFF 300. ALL
DJ1 1 ALL
DJ2 4 ALL
3) If DJ1 and DJ2 are not used, "Deflection Length" will default
to the member length and local deflections will be measured
from the original member line.
4) It is important to note that unless a DFF value is specified,
STAAD will not perform a deflection check. This is in
accordance with the fact that there is no default value for DFF
(see Table 2.1).
5) A critical difference exists between the parameters UNT/UNB
and the parameters LY & LZ. UNT/UNB parameters represent
the laterally unsupported length of the compression flange. It
is defined in Chapter F, page 5-47 of the specifications in the
AISC 1989 ASD manual as the distance between cross sections
braced against twist or lateral displacement of the compression
flange. UNT/UNB parameters are used to calculate the
allowable compressive stress (FCZ and FCY) for behavior as a
beam. LY and LZ on the other hand are the unbraced lengths
for behavior as a column and are used to calculate the KL/r
ratios and the allowable axial compressive stress FA.
6) SSY and CMY are 2 parameters which are based upon 2 values
defined in page 5-55, Chapter H of the AISC 9th ed. manual.
SSY is a variable which allows the user to define whether or
not the member is subject to sidesway in the local Y direction.
CMY is a variable used for defining the expression called Cm
in the AISC manual. When SSY is set to 0 (which is the
default value), it means that the member is subject to sidesway
in the local Y direction. When SSY is set to 1.0, it means that
the member is not subject to sidesway in the local Y direction.
The only effect that SSY has is that it causes the program to
calculate the appropriate value of CMY. If SSY is set to 0 and
CMY is not provided, STAAD will calculate CMY as 0.85. If
SSY is set to 1 and CMY is not provided, STAAD will
calculate CMY from the equation on page 5-55. However, if