This example demonstrates how non-linear cable members can be
modelled in STAAD. In this example, members 1 and 3 are
cables.STAAD PLANEEvery input has to start with the word STAAD. The
word PLANE signifies that the structure is a plane frame (2-D)
structure.SET NL 4This structure has to be analysed for 3 primary
load cases. Consequently, the modeling of our problem requires us
to define 3 sets of data, with each set containing a load case and
an associated analysis command. To accommodate these requirements,
it is necessary to have 2 commands, one called SET NL and the other
called CHANGE. The SET NL command is used above to indicate the
total number of primary load cases that the file contains. The
CHANGE command will come in later (after the PERFORM ANALYSIS
command).UNIT KIP FTUnits for the data to follow are specified
above.JOINT COORD1 0 0 0 ; 2 10 0 0 ; 3 20 0 0 ; 4 10 15 0Joint
coordinates of nodes 1 to 4 are specified. As the structure is a
plane frame, the Z coordinates are all the same, namely, 0.0.MEMB
INCI1 1 4 ; 2 2 4 ; 3 3 4The connectivity of the members (the 2
nodes between which each member is connected) is specified
above.UNIT INCHMEMB PROP AMERICAN1 3 PRIS YD 1.0 ZD 1.02 TA ST
W8x18The cable members are defined as having a rectangular cross
section (1.0 inches X 1.0 inches). The vertical member is assigned
a W8X18 section from the American steel table.MEMBER CABLE1 3
TENSION 50.0The cables are subjected to an initial tension of 50.0
kips.CONSTE STEEL ALLPOISSON STEEL ALLThe material constants,
namely, Modulus of Elasticity, and Poisson's ratio, are specified.
The value assigned happens to be the built-in default value for
steel.SUPPORT1 3 PINNED2 FIXEDNodes 1 and 3 are Pinned supported.
Node 2 is fully restrained.LOAD 1JOINT LOAD4 FX 0.01Load case 1
happens to be a 10 pound force along the global X direction at node
4.PERF CABLE ANALY SAGMIN 0.0 PRINT STATIC CHECKIn order to
instruct STAAD to analyse structures having cable members using the
non-linear analysis approach, the command required is PERFORM CABLE
ANALYSIS. The SAGMIN parameter is specified as having a value of
0.0 to account for full sag E reduction. The static equilibrium
report is sought using the keywords PRINT STATICS CHECK.CHANGEThe
CHANGE command restores the original structure to prepare it for
the analysis for the next primary load case. LOAD 2JOINT LOAD4 FX
40.0Load case 2 consists of a 40 kip force along the global X
direction at node 4.PERF CABLE ANALY SAGMIN 0.0 PRINT STATIC
CHECKCHANGEThe ANALYSIS instruction is specified for the 2nd load
case.LOAD 3JOINT LOAD4 FX 46.3Load case 3 consists of a 46.3 kip
force along the global X direction at node 4.PERF CABLE ANALY
SAGMIN 0.0 PRINT STATIC CHECKCHANGEThe ANALYSIS instruction is
specified for the 3rd load case.LOAD LIST ALLIn a multiple analysis
sequence like the one above, by default, only the last specified
load case is "active" at any given stage. The above command
restores all load cases to the "active" state for further
processing.PRINT JOINT DISPPRINT MEMB FORCESPRINT SUPPORT
REACTAnalysis results, namely, Joint Displacements, Support
Reactions, and Member Forces are requested.FINISH
