Offshore structure seismic design in STAAD PRO

Question

Hi, 
 Can anyone tell how to do seismic design in STAAD PRO for offshore structure i.e. Pipeline End Manifold (PLEM)? 
 Which seismic code to be consider in STAAD PRO for Burma/Myanmar region? 
 Is there any options to input the seismic parameters manually without assigning the STAAD PRO in-built seismic codes? 
 
 I appreciate your help in advance. 
 From 
 Lim

Sudip Narayan Choudhury · Answer

Firstly, it is better to admit my very little understanding of Offshore Structures. I understand that PLEM are structures which ensures proper tie in Subsea Pipelines. If you want to design this in STAAD.Pro, you need to model it first. And I guess that the PLEM is generally composed of I sections/Channels - and thus should not be difficult to model in STAAD. The loading of the pipes should be considered appropriately. 
 
For the Design Code, there are no dedicated Offshore Design Codes in this region and the recommendations of the API code are generally adopted. Claude 2.3.6 (API) of the code gives some guidance on how the seismic loadings should be considered. 
 
In case you are defining a spectra, you can specify custom data in STAAD. You can also generate synthetic time histories from the spectrum data, which I believe can be used to analyse the Offshore structures. You can also generate the Floor Response Spectra which would be important for the analysis. 
 
The Soil-Pile system can also be modelled using appropriate spring stiffness values. STAAD, however, will not be able to calculate the equivalent spring stiffness automatically. 
 
However - there are a couple of things that STAAD will not be able to do. 
 
1. Consideration of the acceleration of the platform under water. STAAD does not consider the "added" mass effect. 
 
2. The Hydrodynamic Drag effects under the motion of the structure would not be considered. 
 
Suggestion: 
 
It is better to use software like SACS which is specialized for Offshore structures to analyze the Offshore Structures. Also, please cross check the above comments with an Offshore Structural Expert.