Understanding Response Spectrum Mode Combination Methods - Lesson 2

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.

Video Highlights

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

Simulation Files

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