Vibration analysis of steel footbridges: Experimental investigation, numerical modeling and theoretical approach

The Academic Center of Agreste, located in Caruaru, in the Northeast of Brazil, consists of pre-cast concrete buildings interconnected by steel footbridge measuring 8.56 meters in length and 2.44 meters in width, along with access ramps to the upper levels, which have an average length of 8.96 meters and a width of 1.67 meters. To enhance the durability of these structures and ensure adequate comfort for users, it is essential to promote regular maintenance and encourage the analysis and installation of vibration control devices, which is the aim of this research. To analyze the mechanical vibrations of the studied footbridge structures, the dynamic behavior was evaluated through three methods. The analytical method was based on the Euler- Bernoulli beam theory. In the experimental phase, the natural frequency and damping ratio were obtained using micro-electro-mechanical systems (MEMS) with a smartphone, utilizing the "myFrequency"app (v. 2.2) for data management, and the structure was excited using the heel drop test. Lastly, numerical analysis was conducted using the finite element method with SCIA Engineer software (v. 22.0). The results indicated that the footbridge achieved a natural frequency of 9.50 Hz experimentally and 12.25 Hz using the analytical and numerical methods, with a damping ratio of 3.70%. For the access ramp, the results were 11.35 Hz, 11.24 Hz, and 14.53 Hz for the experimental, analytical, and numerical methods, respectively, with a damping ratio of 5.04%. Overall, the experimental frequencies were lower than those obtained from the analytical and numerical methods, suggesting variations due to actual support conditions and structural deterioration. These findings emphasize the importance of maintaining the footbridge and access ramps, especially considering the high pedestrian traffic on campus. Furthermore, the research concludes that, although the measured accelerations fall within regulatory limits, it is crucial to conduct further studies to ensure user comfort and the integrity of the structures.