After a major earthquake every building manager asks the same two questions: Is the building safe? Is it usable? Visual inspections take hours, sometimes days, and do not always reveal damage inside the structural system. A structural health monitoring system answers these questions from the building's measured behaviour during the earthquake.
How it works
Accelerometers in the building continuously record small vibrations from wind and traffic on normal days. From these records the building's dynamic signature is identified: modal frequencies, mode shapes and damping ratios. When an earthquake occurs, the system triggers a record, and then:
- modal properties before and after the earthquake are compared,
- inter-storey drift ratios are computed from the measured motion,
- results are compared with threshold values for the building's performance level, and a condition report is produced.
Our team's study in Earthquake Engineering & Structural Dynamics (2024) shows that tracking frequency changes alone is not enough to tell whether a tall building is damaged after an earthquake. Combining frequencies with inter-storey drift ratios estimated through an optimised nonlinear simplified model allows even floors without sensors to be assessed. The study proposes new threshold values for deciding a building's performance level and validates the method on a real earthquake-damaged building.
What about floors without sensors?
Sensors are not needed on every floor. A structural model updated with measurements estimates the motion of non-instrumented floors. Our team applied this approach to three tall buildings in Istanbul: a Timoshenko-beam model updated with measurements estimated the motion of non-instrumented floors, enabling precise drift-based condition assessment. The study also includes modal identification before, during and after an Mw 5.7 earthquake (Bulletin of Earthquake Engineering, 2022).
Where it matters most
Motusmec's software
Motusmec's in-house monitoring software, developed with TÜBİTAK-TEYDEB support (Project No. 2220006), collects vibration records from structures remotely and wirelessly, determines dynamic properties through modal analysis and performs condition assessment quickly after a possible earthquake. Its modules: dynamic identification, condition assessment, fatigue life estimation and video/image processing. Alongside long-term trend reports, it produces automatic event reports after critical events.
Frequently asked questions
Does the system need to be installed before the earthquake?
Yes. Detecting damage requires knowing the building's dynamic properties in its undamaged state, so sensors are installed while the building is healthy and a baseline is built from everyday vibrations.
Does this replace visual damage inspection?
No, it complements it. Measurement-based assessment quickly shows which buildings to inspect first and the overall performance level of a building; it is used together with on-site engineering inspection.
Do we need sensors on every floor?
No. A model updated with measurements estimates the behaviour of floors without sensors. The number and location of sensors are designed for the building's geometry.