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Section 1
1-75
very "flexible" member, viz., when k1>>k2, or k1+k2
≅ k1,
A=1 and hence, 1/(1-A) =1/0. Thus, huge variations in stiffnesses
of adjacent members are not permitted. Artificially high E or I
values should be reduced when this occurs.
Math precision errors are also caused when the units of length
and force are not defined correctly for member lengths,
member properties, constants etc.
Users should ensure that the model defined represents one single
structure only, not two or more separate structures. For example,
in an effort to model an expansion joint, the user may end up
defining separate structures within the same input file. Unintended
multiple structures defined in one input file can lead to grossly
erroneous results.
1.18.2 Second Order Analysis
STAAD offers the capability to perform second order stability
analyses.
See
section 5.37
1.18.2.1 P-Delta Analysis
Structures subjected to lateral loads often experience secondary
forces due to the movement of the point of application of vertical
loads. This secondary effect, commonly known as the P-Delta
effect, plays an important role in the analysis of the structure. In
STAAD, a unique procedure has been adopted to incorporate the
P-Delta effect into the analysis. The procedure consists of the
following steps:
See
section 5.37
1) First, the primary deflections are calculated based on the
provided external loading.
2) Primary deflections are then combined with the originally
applied loading to create the secondary loadings. The load
vector is then revised to include the secondary effects.