Sustained Stresses

• High Priority **

Dear Members,

This is regarding calculation of sustained stresses.

1. The sustained stresses are calculated in sustained load case (Lets call this as SL1) and we are also interested to know that the sustained stresses in operating conditions (Lets call this as SL2) are within the allowable limits. To calculate the sustained stresses in operating condition, we take the active support configuration from the operating load case run and carry out the sustained loading analysis. But sometimes the deflections at the support locations (which are there for calculation of SL1 and to be erected at site), which are removed in calculation of SL2, give unrealistic picture. So the stresses calculated also gives unrealistic values.

For example, if pipe is lifting at a resting support location (S1) by 5mm in operating load case, then this support (S1) is removed and sustained stresses, SL2, are checked. Let us assume that the SL2 are exceeding the allowable , Sh. But if the deflection at the support location (S1) for sustained stress run (SL2) is coming to be 10mm down, then it is an unrealistic deflection, as at site, the support (S1) will be present. The pipe will rest on that support in operating condition after deflecting down by 5mm.

How to take care of this situation? How to calculate the sustained stresses correctly for such situations? Since, in reality, the deflection will be only 5mm down instead of 10mm down, the bending stresses will also be lesser, than what is calculated in the analysis of SL2.

I hope I am clear in my question. In case of doubt please feel free to ask.

Regards,

K. V. JOSHI PRDH-A306,
L&T POWAI WORKS,
MUMBAI-400072
INDIA
TEL: 8581401 Ext. 2880
E-mail : kvj@epc.ltindia.com Received on Sun Nov 25 23:28:00 2001