To establish a proper definition of a rigid material, users must exercise caution regarding two key parameters:
Ensuring that the unit weight of the rigid material is set to 0 is absolutely critical. Failure to do so could lead to the generation of excessive forces due to the self-weight of the rigid section.
To prevent the creation of an ill-conditioned matrix, users must exercise caution when assigning stiffness values, particularly when using high values such as >10000 times E*I or E*A. It is advisable to define stiffness values that are only 100 or 1000 times greater than those of the connected elements.
The below example serves, as an illustration, to grasp the logic behind defining rigid sections by comparing them with other sections within the project:
As observed below, the properties of "Rigid_Section1" are 100 times greater than those of "Column1." Moreover, "RigidMaterial1" has a specified modulus of elasticity of 29000ksi, approximately 6.54 times higher than the modulus of elasticity of “FC_5_1/2ksi” concrete, which is 4428ksi. Consequently, the EI and EA values of the rigid section are 650 times larger than the largest section in the project. Additionally the unit weight of "Rigid_Material1" is explicitly set to 0.
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