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STAAD Commands and Input Instructions
Section 5
5-156
information on this input format. The actual spring constant used
will be the subgrade modulus (f3 entered above) times the
influence area (computed by Staad) times the
s
i
values entered in
the curve (so the curve stiffness values will likely be between 0.0
and 1.0).
SPRINGS d
1
s
1
d
2
s
2
…… d
n
s
n
Example
SUPPORTS
1 TO 126 ELASTIC MAT DIREC Y SUBG 200.
1 TO 100 PLATE MAT DIREC Y SUBG 200.
YR -.01 .01 PLA MAT DIR Y SUBG 200 MUL
SPRINGS -0.51 40.0 -0.50 50.0 0.5 65.0
The first command above instructs STAAD to internally generate
supports for all nodes 1 through 126 with elastic springs. STAAD
first calculates the influence area perpendicular to the global Y
axis of each node and then multiplies the corresponding influence
area by the soil subgrade modulus of 200.0 to calculate the spring
constant to be applied to the node. In the 2
nd
example, the nodes of
plates 1 to 100 are assigned spring supports, generated using a
subgrade modulus of 200 units.
Notes:
A closed surface is generated by the program based on the joint-list that
accompanies the ELASTIC MAT command. The area within this closed
surface is determined and the share of this area for each node in the list is
then calculated.
Hence, while specifying the joint-list, one should make sure that these
joints make up a closed surface. Without a proper closed surface, the area
calculated for the region may be indeterminate and the spring constant
values may be erroneous. Consequently, the list should have at a
minimum, 3 nodes.
The internal angle formed by 2 adjacent segments connecting 3
consecutive nodes in the list should be less than 180 degrees. In other