Forces & Moments

Dr. Frame can display forces and moments in various ways. Color convention, decomposition options, and other display options are discussed here.

Color Convention

Dr. Frame uses the following color convention to distinguish between various classes of forces and moments:

Applied forces & moments (red)

Internal forces & moments (light blue & dark purple, respectively)

Support reactions (green)

Distributed load resultant (light blue)

Decompositions

Vector quantities can be expressed and viewed in any of several reference frames. This is manifested in the inspector tables by a set of popups and i/o cells as shown below:

By default, vector quantities will appear in such tables expressed in terms of the background x-y grid. One can edit magnitude and directions or components directly (directions will be normalized automatically), while for member-based objects, the Vector Basis popup can be used to choose a normal-shear decomposition relative to the associated member when appropriate.

Similar options exist for screen display via the Options>Vector Decomposition menu (or via the '1', '2', and '3' keys):
No decomposition ('1')
x-y decomposition ('2')
normal-shear decomposition ('3')

Other Display Options

Dr. Frame has various other display options available via the Options>Forces & Moments menu (or via quick keyboard commands as indicated):

  • Numerical values can be hidden or shown for forces ('4' key) and moments ('5' key) individually. This can be useful for avoiding screen clutter, among other things.
  • Forces can be drawn either proportional to their magnitude, or with fixed length. Toggle via the period ('.') key.
  • The plotting scale for forces can be adjusted with the Scaling Tools.
  • The effective moment about any desired point can be displayed ('6' key). See the section Working with the Moment Center Tool for more details.
  • Dr. Frame will attempt to draw all joint loads on the "outside" of the structure if the "Forces Out" option is selected. Type 'o' to toggle this option on and off.
Default (forces "in")
Forces out
  • Distributed load resultants can be superimposed as statically equivalent forces. Toggle via the Options>Force & Moment Display>Show Distributed Force Resultants or pressing the '7' key.

In addition to these commands, various scaling controls are available on the scaling tool bar/palette to control label offset distances, moment arc radii, etc. The Working with the X-ray Tool section describes these capabilities in detail.

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