Module 01
What structural dynamics is
Why a structure that passes every static check can still be unusable, and what changes the moment a load arrives quickly enough for the structure's own mass to matter.
What this module covers
- Say what makes a load dynamic, in terms of the structure rather than the load
- Explain inertia as a force, and why it appears in the equation of motion
- Recognise the loadings that commonly cause dynamic problems in practice
- Explain why the same peak load can produce very different responses
- Distinguish a strength problem from a serviceability vibration problem
- Decide, for a given structure and loading, whether a dynamic analysis is needed at all
Lessons
Not how large it is, and not how quickly it changes on its own — but how quickly it changes compared with the structure it is applied to.
Start lesson →The loadings that cause real problems, what each one does, and why most of them threaten usability rather than collapse.
Start lesson →A practical procedure: what to estimate, what to compare it against, and what to do with the answer.
Start lesson →
Module checkpoint
Check what you have taken in
5 questions
Question 1
Two identical loads are applied to two identical structures. One is applied over 5 natural periods, the other over 0.05 natural periods. Which produces the larger response?
Question 2
A mass of 25 tonnes is supported on a structure of lateral stiffness 10 MN/m. What is the natural period in seconds?
Question 3
A beam deflects 5 mm under a load applied slowly. The same load is applied suddenly to a structure with 5% damping. What is the peak deflection in mm? Use DLF = 1 + exp(−ζπ/√(1−ζ²)).
Question 4
An office floor is uncomfortably lively. Which change raises its natural frequency most effectively?
Question 5
A machine runs at 900 rpm on a floor whose natural frequency is 12 Hz. What is the frequency ratio β?