Generally speaking, mode combination methods such as SRSS, CQC, and ROSE are intended for the periodic response, where modal responses are out-of-phase with each other. The rigid response effect can algebraically sum modes that are in the high-frequency range. In the transition region, either the Lindley-Yow or Gupta methods define a fraction of the modal response that is rigid. Although extracted modes can cover the frequency range of interest, they may not have enough effective mass, so the missing mass method provides a technique to account for the inertia forces of the mass not included in the modes. Either or both rigid responses and missing mass responses can be included in a response spectrum analysis. In this video, we will explore how the rigid response and missing mass effects are accounted for to obtain more accurate response spectrum results.
1:05 — Understanding in-phase and out-of-phase responses
2:35 — Determination of the nature of response
4:00 — Understanding the response in the Transition region
5:08 — Lindley-Yow method for defining Rigid Response Coefficient
5:36 — Gupta method for defining Rigid Response Coefficient
6:35 — Understanding the Missing Mass Response
8:00 — Visual representation for calculation of the inertia force for the missing mass
Download the accompanying geometry and archived files here. Download Ansys Student for free here.