| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Report |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Jan. 2017 10.01.00.09 |
Problem:
What is the actual displacement of each node in a modal analysis using AutoPIPE?
Solution:
There are no actual displacements, it just a shape with any amplitude, positive or negative.
Modal Displacements or mode shapes (one and the same) can be Normalized or Mass Normalized to 1. Mass Normalized is more common process and therefore used in AutoPIPE. There are no modal stresses.
Modal analysis is a requirement for all dynamic analysis in AutoPIPE, such as response spectrum, time history, force spectrum and harmonic loads. These analyses will have true displacements and true stresses. Modal displacements are not true displacements and that is why they are commonly normalized to 1 or mass normalized.
Mode shapes or resonance shapes or natural vibration shapes are real and when a system is excited it most likely will vibrate in one or a combination of many mode shapes. It all depends on the loading pattern and loading frequency.