Module 20
Dynamic modelling and software-result checking
The faults that analysis software reports without a warning — missing mass, wrong units, accidental mechanisms, absent diaphragm constraints, too few modes, an unresolved time step — and the checks that catch each one.
What this module covers
- Build a dynamic model whose assumptions match the question being asked
- Check a reported period against a hand estimate before looking at anything else
- Verify the seismic mass against the building's weight, independently of the model
- Detect missing diaphragm constraints, accidental mechanisms and unit errors from the output
- Confirm mode count, time step and convergence from the numbers the software reports
- Write a check that another engineer can repeat
Lessons
Mass, stiffness, damping and constraints — the four modelling decisions that decide whether the analysis is about your building.
Start lesson →Six checks in order, what each one catches, and how to write them down so someone else can repeat them.
Start lesson →
Module checkpoint
Check what you have taken in
4 questions
Question 1
A twelve-storey building is 41 m tall. What first period does T ≈ 0.075H^0.75 predict, in seconds?
Question 2
An analysis reports a base shear of 3 900 kN on a building of seismic weight 52 000 kN. What is the base shear coefficient?
Question 3
A building of plan area 480 m² and twelve floors reports a total seismic weight of 52 000 kN. What is the seismic weight per unit floor area, in kN/m²?
Question 4
A modal analysis of a six-storey frame reports a first mode at 3.9 s carrying 4% of the mass. What does that indicate?