Modal analysis is carried out to determine the various mode shapes of the platform requires the combined Jacket and topsides model to be created in SACS using Preceed-Pro and DataGen modules. The steps are as follows: Make a copy of the sacinp file. Rename the new file and make changes in the LDOPT line from NSM to DYN. Further in the LCSEL change the command from ST to DYN. Specify the retained degrees of freedom as 222000. Normally the corner joints of the jacket and deck are specified as retained DOF’S. Retain only permanent loads on the structure. Remove all other Load Data. Convert all NGDL weights from Buoyant weights to Dry Weights. Assuming that superelement is absent take max reactions from the psilst file and create a single pile analysis file called pilinp.* in which these forces are added using the PLSTUB card. Run single pile analysis and get equivalent pile stub properties .Add these pile stub properties to the sacinp file along with its group and section properties. Create dyninp file and specify number of modes to be extracted. With the modified sacinp and the dyninp file run a analysis in extract mode shapes and check dynlst file for frequency and mass participation factor. This factor should be 95% at least. LARSEN & TOUBRO LIMITED STEP BY STEP GUIDE FOR JACKET DESIGN USING SACS SOFTWARE RESEARCH & DEVELOPMENT ENGINEERING & CONSTRUCTION DIVISION LARSEN & TOUBRO LIMITED
