Product(s):	SACS
Version(s):	23.00.
Area:	Dynamic Response

Problem

What type of Seismic analysis are possible in SACS, by using the output of dynpac module? Can SACS include dynamic wind, wave, and current load in time history seismic analysis?

Solution

For dynamic seismic analysis of multi degree of freedom SACS has 2 types of approaches.

• Response Spectrum Approach:

This is a widely accepted method. This analysis provides the peak responses for each mode. Practically peak responses to all modes are very rare and hence empirical modal combinations are used to consider the total responses. Similarly, peak modal responses for three orthogonal axes are unlikely to occur simultaneously. Hence, responses due to all directions together is determined by spatial combinations.

• Time Domain Approach:

This analysis provides more realistic results since it follows a given accelerogram, unlike response spectrum where peak values are considered. This is very helpful in case of nonlinear structural responses or impact loads. The variation of forces with time should be defined for all the points. SACS development team has prepared a workflow to combine seismic responses with wave responses for SACS V23. 

The basic workflow is:

• Extract Mode Shapes.
• Perform Time History Seismic Analysis and extract force time history. (Seismic analysis must be time history analysis)
• Perform Wave Response Analysis with seismic force time history.
• Run Dynamic Superelement (if exporting responses for integrated wind turbine analyses).