Xi engineers deployed geophones and accelerometers to determine that the high levels of vibration occurred at 7 Hz and were caused by frequency matching between two of the four agitators and a structural resonance of the building. A finite element (FE) computer model was built of the agitator building and calibrated using the measured data.
The FE models were used to calculate the cyclic stress and fatigue life for structural steel elements of the agitator building. Stress hotspots were identified in a number of steel beams close to the base of the agitators. The analysis was used to recommend where structural support should be improved.