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Section 1
1-77
1.18.2.2 Imperfection Analysis
Structures subjected to vertical and lateral loads often experience
secondary forces due to curvature imperfections in the columns
and beams. This secondary effect is similar to the P-Delta effect.
In STAAD the procedure consists of the following steps:
See
section 5.37
and
section
5.26.6
1.
First, the deflections and the axial forces in the selected
imperfect members are calculated based on the provided
external loading.
2.
The axial forces and the input imperfections are then used to
compute an additional loading on the selected imperfect
members that are in compression. These additional loads are
combined with the originally applied loading.
3.
The static analysis is now performed with the combined
loading to obtain the final result.
1.18.2.3 Non Linear Analysis (available in limited
form)
See
section 5.37
REMOVED. Contact Technical Support for further information.
1.18.2.4 Multi-Linear Analysis
When soil is to be modeled as spring supports, the varying resistance
it offers to external loads can be modeled using this facility, such as
when its behavior in tension differs from its behavior in
compression. Stiffness-Displacement characteristics of soil can be
represented by a multi-linear curve. Amplitude of this curve will
represent the spring characteristic of the soil at different
displacement values. The load cases in a multi-linear spring analysis
must be separated by the CHANGE command and PERFORM
ANALYSIS command. The SET NL command must be provided to
specify the total number of primary load cases. There may not be