The input
ELASTIC FOOTING 0 0 DIRECT Y SUBGRADE 0
is not correct. When you are trying to use the Elastic footing option to generate the springs, you need to specify non zero values Length and width of the footing and also for the subgrade modulus. The software calculates the spring stiffness based on these values. All of these show as zero values in the input above. You may refer to the section 5.27.3 of technical reference manual titled Automatic Spring Support Generator for Foundations for more details on this type of input.
Specifying the springs directly using FIXED BUT is fine too. FIXED BUT FX FZ would mean that the nodes are not restrained at these supports against translations in global X and Z. Consequently, if there are applied forces at these nodes then these nodes can translate in these directions and tension can develop in the structural elements associated with these nodes.
ELASTIC FOOTING 0 0 DIRECT Y SUBGRADE 0
is not correct. When you are trying to use the Elastic footing option to generate the springs, you need to specify non zero values Length and width of the footing and also for the subgrade modulus. The software calculates the spring stiffness based on these values. All of these show as zero values in the input above. You may refer to the section 5.27.3 of technical reference manual titled Automatic Spring Support Generator for Foundations for more details on this type of input.
Specifying the springs directly using FIXED BUT is fine too. FIXED BUT FX FZ would mean that the nodes are not restrained at these supports against translations in global X and Z. Consequently, if there are applied forces at these nodes then these nodes can translate in these directions and tension can develop in the structural elements associated with these nodes.