Experimental Investigations on the Flutter Derivatives of the Pedestrian-Bridge Section Models
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-0243-7
Structural Engineering
Experimental Investigations on the Flutter Derivatives of the Pedestrian-Bridge Section Models Yu Li
a
and Chen Lib
a
School of Highway, Chang'an University, Xi'an 710064, China School of Architecture, Chang'an University, Xi'an 710061, China
b
ARTICLE HISTORY
ABSTRACT
Received 11 February 2020 Accepted 7 July 2020 Published Online 10 September 2020
Based on a suspension footbridge, the pedestrian-bridge section models were first proposed and designed. Then, the free vibration tests were carried out to study the influence of pedestrians on the flutter derivatives (H1*, A2*, A3*, H4*, and A1* × H3*) which significantly affect the flutter of suspension footbridges. It can be found that: 1) with an increase in the pedestrian density, the H1*, H4* and A1* × H3* increase, which will lead to the decrease in the positive vertical aerodynamic damping, the positive vertical aerodynamic stiffness and the positive vertical and torsional aerodynamic damping, respectively. Meanwhile, with an increase in the pedestrian density, the A2* and A3* decrease, which will lead to a decrease in the negative torsional aerodynamic damping and the negative torsional aerodynamic stiffness, respectively. 2) The arrangement of walking side by side is advantageous to the positive vertical aerodynamic damping and disadvantageous to the negative torsional aerodynamic stiffness. The arrangements of random walking with low-medium pedestrian densities and walking in line with high-medium pedestrian densities are disadvantageous to the vertical aerodynamic stiffness and the positive vertical and torsional aerodynamic damping. Besides, all the pedestrian arrangements have a significant influence on the torsional aerodynamic damping.
KEYWORDS Suspension footbridge Free vibration test Pedestrian-bridge system Flutter derivative Pedestrian density
1. Introduction It is well known that flutter derivatives are the essential parameters for evaluating the flutter stability of bridges, and can be determined through wind tunnel tests such as free vibration tests or forced vibration tests. With less demanding of experimental facilities, free vibration tests are more popular in obtaining the flutter derivatives (Hi* and Ai* (i = 1, ..., 4)) of bridge decks (Chowdhury and Sarkar, 2003). According to the previous studies for the bluff section (Ding et al., 2010; Han et al., 2014; Xu et al., 2014; Andersen and Brandt, 2018), it can be known from the derivation of 2-DOF coupled flutter vibrations that: the direct derivatives (H1*, A2*, A3* and H4*) have a significant influence on the aerodynamic damping and stiffness of the system; the influence of the cross derivatives (H2*, A1*, A4* and H3*) on the system vibration is represented by the combined effects. At present, many scaled section models of vehicular bridge decks are tested to evaluate the flutter derivatives (Scanlan et al., 1997; Sarkar et al., 2009; Baldomir et al., 2013), and several
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