STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

nivassrii · SEFI Member Joined: 16 Mar 2012 Posts: 15

Dear Sefians,

I have to design a raft foundation to support 6no.s of columns of a pipe rack for which I prepared i) One finite element model with primary load cases along with Load combinations and ii) Another finite element model with primary load cases along load cominations as primary load cases using "Repeat Load" command.

The problem I am facing is with the interpretation of results as follows:

Design forces like Base pressures, Bending Moments and Shear stresses obtained from both of these two models differs largely from each other.

Kindly clarify me the following points.

1. How these two cases are different from each other, if possible please explain with a easy understand example.

2. Which of these two shall be considered for the design of raft and why?

3. Can we use the " Repeat Load " for the analysis and design of beam and column members?

Also, please clarify the following too.

1. Whether STAAD considers axial

nivassrii · SEFI Member Joined: 16 Mar 2012 Posts: 15

Somebody please reply...

k.sankarasubramanian · ... Joined: 01 May 2011 Posts: 80

rahul.leslie · Posted: Tue Nov 26, 2013 9:55 am Post subject:

It comes as a surprise to me to find that you ARE getting different answers, while you have NOT MENTIONED of using P-Delta or Non-linear analysis.

Rahul Leslie

veerababudodda · SEFI Member Joined: 16 Sep 2009 Posts: 14

Hi srinu,

The results will be different when you perform non-linear analysis.

The below link explains the difference between repeat load and combined load.

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/3441.aspx

Regards,
Babu

gpsarathyy · ... Joined: 28 Jun 2010 Posts: 487

Dear Sefians,

Using "Repeat load" command and using "Load combinations" should not result in different values. Unless you are using it for P-delta analysis or any non-linear analysis etc., Please check the analysis and results once again before concluding.

sandipdeb · SEFI Member Joined: 21 Jun 2020 Posts: 2

If the structure is undergoing a non-linear analysis such as P-Delta analysis, buckling analysis, or any analysis that involves non-linear behavior (like cables or tension-only members), REPEAT LOAD is necessary to ensure that loads are applied together, considering the load path and sequence of application.

When the order in which loads are applied matters for the analysis, such as staged construction or specific structural behavior under multiple load conditions, REPEAT LOAD ensures the actual application sequence is followed.

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