Multi Linear Spring Support
To assign the multilinear attribute to the support which is basically a plot of displacement vs corresponding spring stiffness at that displacement. One should start with the most negative displacement and the corresponding stiffness and then go to the most positive value of displacement and its corresponding stiffness value.
The non-linear behavior of the soil (such as when its behavior in tension differs from its behavior in compression) can be modeled using multi-linear supports. Please note here that these supports presents a non-linear condition so, they will initiate an iterative analysis to be separated by the CHANGE command and PERFORM ANALYSIS command. The SET NL command must be provided to specify the total number of primary load cases and convergence check cycle. General Format: Support 100 Pinned 200 400 FIXED BUT KFY 40. MultiLinear Springs 200 400 Spring -1 40 -5 50 … Multilinear springs should not be used in the following conditions: Modal dynamics Buckling analysis Imperfection analysis PDELTA analysis NONLINEAR analysis Advanced cable analysis Direct analysis Models with tension/compression members and/or supports Models with inclined supports