Abstract
High-speed rail stations have long-span floor structures stretching over rail tracks and platforms. These long-span floor structures are prone to vibration caused by large crowds. Current floor vibration design guidelines lack specific provisions addressing this type of structures. There is a need to study the crowd excitation and the vibration performance of the long-span floor structures. A field testing study was recently conducted in China’s newly constructed Xi’an North Railway Station, and results of the study is discussed in this paper. The output-only method was used for modal testing, where vertical accelerations were recorded at a grid of fifty locations on the floor panels and analyzed to obtain the natural frequencies, mode shapes, and damping ratios of structural vibration modes. Vibration measurements were taken and analyzed at a variety of load cases, which included operating cases at the floor sections in use to assess vibration performance of the floor structure, and several experimental cases at the floor sections not yet in use to investigate the effects of crowd size and walking and jumping frequency on floor vibration. It was found that under most operating conditions, the floor structural vibration didn’t exceed the commonly accepted design limits. Thus, the vibration control design of the floor structure is deemed satisfactory. Under certain coordinated crowd movements (e.g., walking and jumping at certain frequencies), resonance occurred, and vibration levels exceeded the threshold for acceptance. The crowd excitation frequency has a greater influence than the crowd size on floor vibration responses.
Highlights
Long-span floor structures in public buildings, such as airports and train stations, are prone to vibrations caused by large moving crowds
In order to investigate the effects of crowd size and crowd excitation frequency on the floor vibration, several experimental cases were conducted in Section D (Panels D1 and D2, see Fig. 1) of the concourse floor which was not open for operation at the time of this study
First a rolling two-second root-mean-square (RMS) values were computed from measured records, the computed RMS values were multiplied by square root of two (√2) to get the Equivalent Sine Peak Acceleration (ESPA) values
Summary
Long-span floor structures in public buildings, such as airports and train stations, are prone to vibrations caused by large moving crowds. Due to their unique structural systems and the randomness in crowd movements, current floor vibration design guidelines do not adequately address vibrations of this type of structures. Researchers from Tufts University studied train-induced vibration in buildings and developed an impedance-based predictive model to evaluate vibration transmission in building columns and conducted scaled model testing [13]. They proposed a vibration transmission mitigation method by increasing the thickness of a lower floor slab. The vibration performance of the floor structure was assessed by the measured results, and crowd excitation parameters that affect the floor vibration were analyzed and compared
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