In a response spectrum analysis, we first obtain the individual modal responses to an input response spectrum. Then, different mode combination methods are used to approximate the maximum response of the structure. In Ansys Mechanical, three types of mode combination methods are available, square root of the sum of squares (SRSS), complete quadratic combination (CQC) , and Rosenblueth (ROSE). The SRSS method does not account for the modal coupling between different modes, whereas the CQC and ROSE methods account for the interaction of modes that are close to each other. In this video lesson, we will explore how mode combination methods are specified, and how different methods affect the results.
02:12 - General equation of mode combination methods
02:29 - The coupling coefficient
04:28 - Square root of the sum of the squares (SRSS) method
05:07 - Rosenblueth (ROSE) method
06:18 - Complete quadratic combination (CQC) method
09:40 - How to specify the mode combination method in Ansys Mechanical
Download the accompanying geometry and archived files here. Download Ansys Student for free here.