The SAP2000 bridge modeler and CSiBridge create creates rigid constraints (restraints), such as with fixed bearings, by applying large stiffness values to link and spring objects. This allows the software to calculate forces which may not be computed when links are bound by truly fixed DOF. This also avoids instability issues which may arise when constraints are coupled. SAP2000 and CSiBridge provide for coupled constraints, though users should take precaution.
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