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*TO DO:* * Migrate Body vs. Equalequal constraint-test Test problem 1 from migration1d to Constraint test problems.
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An *equal constraint* is applied to [joints|kb:Joint] such that theirequal displacement isoccurs equal along eachthe translational DOF specified. ThereNo iscoupling no couplingoccurs between translation and rotation, whichdifferentiating differentiates an equal constraint from a [body constraint|kb:Constraint]. Equal constraints are useful for modeling expansion joints and locations where two elements connect to form a hingeslot-pin connection, as is described in the [Modeling pinned connections between crossing members|tutorials:Modeling a pin connection between crossing members] tutorial.

Body constraints should be used, rather than equal constraints, to To fully connect [meshes|kb:Meshing] which do not share common joint locations, body constraints should be used, rather than equal constraints. Otherwise, the constraint may restrain the system against certain types of behavior, thus stiffening the model, and generating moment unrealistic moment values. This will affect analysis and may lead to the reportreporting of a lack constraintof forcesequilibrium notamong inconstraint equilibriumforces.

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h2. Why do equal constraints affect analysis when body constraints should be applied?

*Extended Question:* The {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc:CSI Analysis Reference Manual] (Equal Constraint, page 59) states that equal constraints may unrealistically stiffen the structure when applied between meshes which do not share common joints. Is an explanation and an example available?

*Answer:* Please refer to the [Body vs. equal constraint|migration1d:Body vs equal constraint-test problem 1] test problem for response.

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