Bentley 2006 User Manual

 

STAAD Commands and Input Instructions 

 Section 5

 

 

direction spring goes slack, the X and Z springs at the same joint 
are made inactive as well. 
 
The procedure for analysis of Tension-only or Compression-only 
springs requires iterations for every load case and therefore may be 
quite involved. 
 
Since this command does not specify whether the spring is in the 
positive or negative direction from the joint, it is assumed in 
STAAD to be in the negative direction.  For negative displacement 
the spring is in compression and for positive the spring is in 
tension. 
 
If a CHANGE command is used (because of a change in list of 
tension springs, supports, etc.), then the SET NL command must 
be used to convey to STAAD that multiple analyses and multiple 
structural conditions are involved.  
 
Example  

 
Notes 
 
1)  A spring declared as TENSION only or COMPRESSION only 

will carry axial forces only.  It will not carry moments. 

2)  The SPRING TENSION / COMPRESSION commands should 

not be specified if the INACTIVE MEMBER command is 
specified. 

3)  Do not use Load Combination to combine these cases.  

Tension/Compression cases are non-linear and should not be 
linearly combined as in Load Combination.  Use a primary 
load case with the Repeat Load command. 

4)  The following is the general sequence of commands in the 

input file if the SPRING TENSION or COMPRESSION