We recommend using sufficiently large stiffness values on the order of 1e11 kN-m (or kN-m/rad) to model the rigid behavior of concrete systems. Formulation is explained in the Bearing and foundation springs article. Sufficiently rigid stiffness values may be assigned using spring constants, property modifiers, section properties, or any other method which will produce the desired effect. This modeling procedure is typically adequate when rigid stiffness is not too large relative to the stiffness of connecting elements. Otherwise, linear problems may experience numerical sensitivity, and nonlinear problems may fail to converge. Restraints and constraints may be used to avoid these computational issues, but forces will not be generated, and additional problems may result from coupling behavior.
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