TR.27.1 Global Support Specification
This set of commands may be used to specify the SUPPORT conditions for supports parallel to the global axes.
For SURFACE elements, if nodes located along a straight line are all supported identically, as in the case of the base of a wall, support generation can be performed for assigning restraints to those nodes. See the GENERATE option in the command syntax below. You only need to provide the starting and ending nodes of the range, and the type of restraint.
General Format
SUPPORTS
{ joint-list | ni TO nj GENERATE } { PINNED | FIXED ( BUT release-spec (spring-spec) ) | ENFORCED ( BUT release-spec) }
release-sepc = { FX | FY | FZ | MX | MY | MZ }
spring-spec = *{KFX f1 | KFY f2 | KFZ f3 | KMX f4 | KMY f5 | KMZ f6 }
Where:
- ni, nj = Start and end node numbers, respectively, for generating supports along a SURFACE element edge.
- f1 … f6 = Spring constants corresponding to support spring directions X, Y, and Z and rotations about X, Y, and Z, repsectively.
Description of Pinned and Fixed
A 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 f1 through f6. 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.
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See TR.38 Change Specification for information on specification of SUPPORTS along with the CHANGE command specifications.
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Spring constants must be provided in the current units.
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All spring DOF must be entered after the last non-spring DOF is specified, if both are on the same line.
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If there are two entries for the same joint, then:
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any direction that is pinned/fixed on either will be fixed in that direction.
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any direction released on one and is a spring on the other will use the spring.
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any direction that is pinned/fixed on one and a spring on the other will use the spring.
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any direction that is a spring on two or more entries will have the spring constants added.
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Example 1
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.
Description of Enforced
Enforced Support defines which translational and rotational directions, at a joint, may have a support displacement imposed. The support displacements are defined for each load case in TR.32.8 Support Joint Displacement Specification. If no support displacement is entered, then zero displacement will be imposed, as if that direction was FIXED. The enforced displacement directions will be fixed for dynamic load cases.
If there are two entries for the same joint, then any direction that is enforced on either will be enforced in that direction, overriding any other support specification for that joint-direction.
Currently the support generation command can only be used in conjunction with the Surface element support specifications.
Example 2
SUPPORTS 3 TO 7 GENERATE PIN
The above command will generate pinned supports for all joints located between nodes No. 3 and 7 along a straight line. This may include joints explicitly defined by the user or joints generated by the program for internal use only (e.g., as a result of SET DIVISION and SURFACE INCIDENCES commands).