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STAAD Commands and Input Instructions
Section 5
5-158
5.27.4 Multi-linear Spring Support Specification
When soil is modeled as spring supports, the varying resistance it
offers to external loads can be modeled using this facility, such as
when it becomes stiffer as it is compressed. Another application of
this facility is when the behavior of soil in tension differs from its
behavior in compression.
General format:
MUL
TILINEAR SPRINGS
joint-list SPR
INGS d
1
s
1
d
2
s
2
…… d
n
s
n
where (di si) pairs represent displacement and spring constant
pairs (si is zero or positive), starting from the maximum negative
displacement to the maximum positive displacement.
See Section
5.27.5 also
The first pair defines the spring constant from negative infinity
displacement up to the displacement defined in the second pair.
The second pair define the spring constant when the support
displaces in the range from the displacement defined in the second
pair, up to the displacement defined in the third pair. This
continues for each displacement and spring constant pair until the
last pair which defines the spring constant for displacements
greater than the displacement in the last pair to positive infinity.
Example
UNIT …
SUPPORT
1 PINNED; 2 4 FIXED BUT KFY 40.0
MULTILINEAR SPRINGS
2 4 SPRINGS -1 40.0 -0.50 50.0 0.5 65.0