Modal analysis is a vital technique in structural dynamics used to identify a structure’s natural frequencies, mode shapes, and damping characteristics, thereby providing insights into its dynamic behavior under different loading conditions. Medha SMH Rail, after developing new monorail vehicles for the Mumbai Monorail, aimed to study the modal responses of the structural beam during operation. A Finite Element Model (FEM) of the beam had already been developed, and experimental modal analysis was undertaken by NV Dynamics to correlate the FEM results.
The experimental study was carried out on a straight monorail beam section and its supporting columns under two conditions: no - load (empty beam) and loaded (with a monorail car). Sixteen response locations were identified, eight on the beam and four on each pier, along with two driving points located at the beam’s midpoint and quarter point for impact hammer excitation. Vibration transducers were installed at all response and driving points and all transducers were connected to synchronized multi-channel data acquisition systems. Signal checks for reciprocity and linearity were performed to ensure reliable data before testing. Once the data confidence was established the modal tests were conducted.
The modal and vibration analysis successfully determined the structure’s natural frequencies, damping ratios, and mode shapes. Experimental results closely matched the FEM predictions, validating the model and confirming the beam’s dynamic behavior. Additional vibration data from monorail pass-by tests further verified the results, ensuring the monorail’s structural safety and operational efficiency under real-world conditions.
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