SHEAR-MOMENT DIAGRAMS
Overview
REPTILE can be used to quickly generate shear and moment diagrams (sometimes called VMT or PVM diagrams) across many load cases and output files in a single step. This functionality is typically useful when analyzing a structure with many similar section cuts.
<< insert example shear/moment diagram >>
<< insert example shear/moment diagram >>
Definition File
In order to generate shear and moment diagrams, REPTILE needs 3 things:
- A list of elements which comprise the structure under consideration
- A coordinate system and its origin
- A list of locations at which to calculate shears and moments
# OPTIONAL COMMENT LINE(S)
DEF BEAM_ABC_
ELEMS 41 42 43 44 45
ORIGIN 19.27 -4.88 98.09
CSYS1 15.62 -1.34 104.61
CSYS2 1002
CSYS3 1003 1005
LOC X 0.25 5.75 12.50 19.75 22.25
The Definition File consists of blocks of input associated with the shear moment diagram. Indentation is not required, but it recommended purely for readability. Comments can be added to help document the input file as the user sees fit. Comment lines begin with the "#" character.
The block begins with the "DEF" keyword followed by a name, which is used as a prefix in the "ID" column of the CSV output. After that, the inputs for the shear/moment diagram follow (in any order).
The "ELEMS" keyword is identical to that used in the definition file for REPTILE's Grid Point Force Summation mode.
The "ORIGIN" keyword defines the origin (location 0.0) for the shear/moment diagram, and is almost identical to the "SUMPT" keyword in REPTILE's Grid Point Force Summation mode.
The coordinate system is defined identically to REPTILE's Grid Point Force Summation mode.
The "LOC" keyword defines a list of location at which to calculate shears and moments. It consists of the "LOC" keyword followed by a direction in the coordinate system (X, Y, or Z) followed by a list of numerical distances from the ORIGIN along that direction. NOTE: If no locations are specified, REPTILE will calculate shears and moments at every node associated with the elements defined by "ELEMS." This might be convenient for some applications, but it may also result in "jaggies," or noise-like discontinuities in the shear and moment diagrams.
The block begins with the "DEF" keyword followed by a name, which is used as a prefix in the "ID" column of the CSV output. After that, the inputs for the shear/moment diagram follow (in any order).
The "ELEMS" keyword is identical to that used in the definition file for REPTILE's Grid Point Force Summation mode.
The "ORIGIN" keyword defines the origin (location 0.0) for the shear/moment diagram, and is almost identical to the "SUMPT" keyword in REPTILE's Grid Point Force Summation mode.
The coordinate system is defined identically to REPTILE's Grid Point Force Summation mode.
The "LOC" keyword defines a list of location at which to calculate shears and moments. It consists of the "LOC" keyword followed by a direction in the coordinate system (X, Y, or Z) followed by a list of numerical distances from the ORIGIN along that direction. NOTE: If no locations are specified, REPTILE will calculate shears and moments at every node associated with the elements defined by "ELEMS." This might be convenient for some applications, but it may also result in "jaggies," or noise-like discontinuities in the shear and moment diagrams.
Example Command Lines
REPTILE can be invoked from a batch script (recommended) or from a command prompt (not recommended), but in either case, the command lines look the same. See Getting Started for more information.
The Shear/Moment Diagram mode requires 3 command line arguments:
So a minimal shear/moment command line might look like this:
The Shear/Moment Diagram mode requires 3 command line arguments:
- An Input File (as described above)
- An Output Filename (output is in CSV format by default)
- The XDB File(s) to process (wildcards are allowed)
So a minimal shear/moment command line might look like this:
reptile --vmt -i Input_File.def -o Output_File.csv file1.xdb
Of course, wildcards are allowed for the XDB Files, so if you have a lot of XDB Files, you might do this:
reptile --vmt -i Input_File.def -o Output_File.csv file*.xdb
Now lets say you want to output to a SDIO and perform Load Combinations. First, we need to add a "-SDIO" option which tells REPTILE to generate a SDIO file after it creates the CSV file (See SDIO Output for more info). Note: It doesn't matter where in the command line you put a option like this. Second, instead of giving REPTILE one or more XDB Files, we use the "-COMB" option and give it the name of the file that defines the load combinations (this file will point to the appropriate XDB Files) (See Load Combinations for more info).
So the final command line will look like this:
So the final command line will look like this:
reptile --vmt -i Input_file.def -o Output_File.csv -SDIO -COMB file.comb
OTHER OPTIONS
-SES file.ses
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Writes out a Patran session file that creates groups for each free-body cut.
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-FBDY
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In conjunction with the "-SES" option, this option adds commands to the Patran session file to create a geometric point at the summation point and two vectors to define the coordinate system.
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-FLIP
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Swap the signs of the grid point forces to use the force applied to the element at the node, rather than the force applied to the node by the element (which is the default). Using "-FLIP" will cause the output to match the MSC.Patran "Freebody" convention.
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