# D8.E.4 Slenderness Effects and Analysis Consideration

STAAD.Pro uses of the first option. To perform this
type of analysis, use the command `PDELTA ANALYSIS` instead of
`PERFORM ANALYSIS`. The P-Delta analysis will accommodate all
requirements of the second- order analysis described by IS:456, except for the effects of
the duration of the loads. It is felt that this effect may be safely ignored because
experts believe that the effects of the duration of loads are negligible in a normal
structural configuration.

Although ignoring load duration effects is somewhat of an approximation, it
must be realized that the approximate evaluation of slenderness effects is also an
approximate method. In this method, additional moments are calculated based on empirical
formula and assumptions on sidesway (Clause 39.7.1 and 39.7.1.1,IS: 456 - 2000). The rules
of Clause 39.7.1 have been implemented in STAAD.Pro. They
will be checked if the `ELY` and `ELZ` parameters are
specified.

Considering all these information, a P-Delta analysis, as performed by STAAD.Pro may be used for the design of concrete members.

`REPEAT LOAD`command.