Question
For underground structures that use compression-only point springs, singular error occur.
Answer
For correct analysis, it is necessary to define the simultaneous loads as a single load case so that the loads act simultaneously during the analysis.
The above model is an example that uses compression-only spring supports to consider the compressive characteristics of the soil supporting the structure.
In this case, when subjected to positive hydraulic pressure or asymmetric horizontal soil pressure, the compression-only spring supports experience tensile forces and they will lose their function as springs.
However, since structures are not subjected to only positive hydraulic pressure or asymmetric horizontal soil pressure but rather multiple loads including self-weight act simultaneously. Therefore, it is meaningless to consider the occurrence of tensile springs for individual load cases. Also, when using load combinations, the results of individual load cases are combined, which also results in meaningless outcomes. For appropriate analysis, it is necessary to define the simultaneous loads as a single load case so that the loads act simultaneously during the analysis.
To do that, select Load tab > Static Loads (Type) group > Using Load Combinations.
The load combinations should be converted to load cases so that the loads act simultaneously on the structure.
At this point, the individual load cases used in the load combinations should be deleted to prevent the occurrence of Singular Errors due to boundary conditions.