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STRUCTURAL ANALYSIS AND DESIGN - FORUM

P-DELTA ANALYSIS 

Posted bychaz 

on Tue, Dec 4 2012 8:53 AM 

  Technical Reference Manual 

  5.37.2 P-Delta Analysis Options 

  Used to perform a second-order analysis, considering either large- or small-delta effects—or

both—on the structure.

1.  P-Delta analysis with Small & Large Delta effects or Large Delta effects only. With this

option the global forces are adjusted with every iteration

PDELTA (n) ANALYSIS (CONVERGE (m)) ( { LARGEDELTA | SMALLDELTA } ) (PRINT  print-

options)

Where:

n = no. of iterations desired (default value of n = 1).

m = the maximum number of iterations used to check convergence, even if

convergence has not been achieved. Do not  use CONVERGE when n is specified.

SMALLDELT is the default 

  Based on the above section of the technical reference manual, how to perform second order

analysis considering both small delta and large delta effect on STAAD.Pro???

  second order analysis, large delta, P-delta analysis, small delta 

 

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Posted byKris Sathia 

on Tue, Dec 4 2012 10:51 AM 

  In versions of STAAD created during the past 3-4 years, the following command will ensure that

both effects are considered.

  PDELTA 30 ANALYSIS SMALLDELTA

  If you have a version of STAAD created during the past 6-12 months (V8i SS3 and SS4), the word

SMALLDELTA is not needed, as in the following example.

  PDELTA 30 ANALYSIS

  But no harm in including it.

P Delta and Linear Anaylsis 

Posted byAnonymous

on Mon, Dec 13 2010 5:18 PM 

  I am wonderinf if there a way to do both a P Delta analysis and a linear analysis together and

have the two different results displayed next to eachother so I can compare them

  Thanks for any help offered

 

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Posted bySKLose 

on Tue, Dec 14 2010 6:13 AM 

  Here is a hypothetical example. In this example, Load 1 is the vertical load. Load 2 is the lateral

load.

  To obtain the combined effect of these, one with a simple linear analysis, and the other with a

PDelta, create two combination cases.

  Load 11 is the combination for examining the PDelta effect. Since this does not satisfy the

principle of superposition, we combine the two cases using the REPEAT LOAD syntax.

  Load 12 is the linear combination for linear elastic analysis that does not include the Pdelta effect.

Since this satisfies the principle of superposition, the combination can be done using the "LOAD

COMBINATION" syntax.

  LOAD 1 GRAVITY LOAD

  SELF Y -1.0

 

LOAD 2 LATERAL LOAD

  JOINT LOAD

  3 TO 6 FX 1.5

  PERFORM ANALYSIS

  LOAD 11 GRAVITY + LATERAL

  REPEAT LOAD

  1 1.0 2 1.0

  LOAD COMBINATION 12 GRAVITY + LATERAL

  1 1.0 2 1.0

  PDELTA 30 ANALYSIS SMALLDELTA

  Load case 11 will be analysed by solving the expression {d} = [Kinv]{P1 + P2}

  Load case 12 will be solved by algebraic addition of {d1} and {d2} where {d1} and {d2} are the

displacements for cases 1 and 2 respectively. The resulting displacements are used to compute

member forces and support reactions.