Question
'Singular Error' occurs when analyzing a simple beam with pin and roller at the ends.
Answer
First, it is necessary to decide whether a 3D or 2D structural analysis is to be performed in the 'Structure Type'. Then, you should apply the appropriate boundary conditions accordingly.
1. Structural analysis of a structure with 2D boundary conditions in 3D.
The above model is a simple beam in which the structure, load, and reaction force acting on it are in the same plane. While modeling the beam with hinge and roller at the ends, an error can occur when you constrain only the displacement in the X-axis and Z-axis direction and rotation along the X-axis. However, since Midas Civil performs 3D analysis by default if the rigid body motion is not constrained by additionally fixing displacements in the Y-direction and rotation about the Z-axis, the structure becomes unstable and a singular error occurs.
As a result, since the program recognizes the structure as a 3D structure by default, you need to fix additional Y-directional displacement and Z-axis rotational displacement.
Alternatively, if you select the proper 2D plane in Structure> Type> Structure Type, unnecessary boundary conditions are automatically constrained and you only need to define boundary conditions associated with 2D analysis. For example, if you select the X-Z plane, Dy, Rx, and Rz are automatically constrained.
2. Analyzing a 3D structure with 2D boundary conditions
Above model is a 3D frame model with loads and reactions not in the same plane as the structure. Although it is a 3D model, there are cases where the model is analyzed by selecting the X-Z plane in Structure > Type > Structure Type.
In such cases, the Y-directional displacement and Z-axis rotational displacement are automatically constrained in the model, so the analysis can be performed without any problems, but abnormal results will appear.