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Section 5
5-147
Description of Pinned and Fixed
PINNED support is a support that has translational, but no
rotational restraints. In other words, the support has no moment
carrying capacity. A FIXED support has both translational and
rotational restraints. A FIXED BUT support can be released in the
global directions as described in release-spec (FX for force-X
through MZ for moment-Z). Also, a FIXED BUT support can have
spring constants as described in spring-spec (translational spring
in global X-axis as KFX through rotational spring in global Z-axis
as KMZ). Corresponding spring constants are f
1
through f
6
. The
rotational spring constants are always per degree of rotation. All
six releases may be provided as may be required when using the
CHANGE command. If both release specifications and spring
specifications are to be supplied for the same support joint, release
specifications must come first.
See Section
1.14
Example
SUPPORTS
1 TO 4 7 PINNED
5 6 FIXED BUT FX MZ
8 9 FIXED BUT MZ KFX 50.0 KFY 75.
18 21 FIXED
27 FIXED BUT KFY 125.0
In this example, joints 1 to 4 and joint 7 are pinned. No moments
are carried by those supports. Joints 5 and 6 are fixed for all DOF
except in force-X and moment-Z. Joints 8 and 9 are fixed for all
DOF except moment-Z and have springs in the global X and Y
directions with corresponding spring constants of 50 and 75 units
respectively. Joints 18 and 21 are fixed for all translational and
rotational degrees of freedom. At joint 27, all the DOF are fixed
except the FY DOF where it has a spring with 125 units spring
constant.