I. Principle of Vibration Parameter Measurement of Bailey Bridge
The vibration characteristics of a Bailey Bridge are similar to the human pulse, reflecting the structural health condition. The measurement of mode shapes, frequencies and damping ratios follows three steps:
Sensor Arrangement: Install accelerometers at key positions of the bridge deck to capture the vibration responses of each point.Excitation Methods: Ambient vibration (vehicle passage) or artificial excitation (hammering method) can be adopted.Data Synchronization: All sensors must be time-synchronized to ensure accurate phase relationships.
II. Acquisition Methods of Core Parameters
The three key parameters constitute the "physical examination report" of the bridge:
Frequency Measurement: Identify the hertz value corresponding to the peak through spectrum analysis.Mode Shape Identification: Normalize the amplitude of each measuring point and plot the spatial vibration form.Damping Ratio Calculation: The half-power bandwidth method is commonly used to measure the width of the resonance peak.
III. Notes for Field Operation
The following obstacles may be encountered in field measurement:
Insufficient number of sensors will result in distortion of mode shapes.Ambient noise may mask the real frequencies.Temperature changes affect material stiffness, leading to frequency drift.Outliers must be eliminated during data processing to avoid "false positive" judgments.