Structural dynamics / tutorial
Auditing an analysis you did not run
Six checks in order, on an output that looks entirely normal.
Teaching basis and review status
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesA subconsultant has issued a modal and response-spectrum analysis of a nine-storey concrete frame. The report is neat, the mode shapes are plotted, and there are no warnings. Run the checks before reading a single member force.
- Nine storeys, 31 m tall, plan 540 m²
- Reported first period 0.38 s
- Reported total seismic weight 47 000 kN
- Reported base shear 18 000 kN
- Reported first-mode effective mass 74%; cumulative over 9 modes 97%
Practice
What first period does the rule T ≈ 0.075H^0.75 predict, in seconds?
Practice
What is the seismic weight per unit floor area, in kN/m²?
Practice
What is the base shear coefficient?
Practice
By what factor is the model's stiffness in error, taking the expected period as 0.985 s?
Ten minutes, four numbers, and the whole submission is established as unusable before anyone opened a drift table. Note also what passing all six checks would NOT have established: only that no fault of these kinds is present, which is a much weaker and more honest statement than 'the analysis is correct'.