Experimental Investigation on the Nonlinear Coupled Flutter Motion of a Typical Flat Closed-Box Bridge Deck.

Guangzhong Gao,Feng Wang,Ledong Zhu,Jianming Hao,Hua Bai

doi:10.3390/s20020568

Guangzhong Gao, Feng Wang + Show 3 more

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https://doi.org/10.3390/s20020568

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Abstract

The nonlinear post-flutter instabilities were experimentally investigated through two-degree-of-freedom sectional model tests on a typical flat closed-box bridge deck (width-to-depth ratio 9.14). Laser displacement sensors and piezoelectric force balances were used in the synchronous measurement of dynamic displacement and aerodynamic force. Beyond linear flutter boundary, the sectional model exhibited heave-torsion coupled limit cycle oscillation (LCOs) with an unrestricted increase of stable amplitudes with reduced velocity. The post-critical LCOs vibrated in a complex mode with amplitude-dependent mode modulus and phase angle. Obvious heaving static deformation was found to be coupled with the large-amplitude post-critical LCOs, for which classical quasi-steady theory was not applicable. The aerodynamic torsional moment and lift during post-critical LCOs were measured through a novel wind-tunnel technique by 4 piezoelectric force balances. The measured force signals were found to contain significantly higher-order components. The energy evolution mechanism during post-critical LCOs was revealed via the hysteresis loops of the measured force signals.

Highlights

Flutter is the most dangerous aeroelastic instability for modern long-span bridges
When wind velocity exceeds beyond linear flutter boundary, there is a possible existence of nonlinear post-critical limit cycle oscillation (LCOs) due to the aerodynamic nonlinearity
Sectional model tests were performed in TJ-1 Wind Tunnel, which is a sucking-type open-circuit wind tunnel located in Tongji University

Summary

Introduction

Flutter is the most dangerous aeroelastic instability for modern long-span bridges. Flutter instability is conventionally treated as a linear eigenvalue problem by classical linear flutter theory [1]. According to the linear theory, flutter instability occurs when the real part of a complex eigenvalue becomes negative and the vibration manifests as an exponential increase of vibration amplitude with time. Classical linear theory is based on a small-amplitude assumption and ignores any possible aerodynamic nonlinearity under large amplitude; the predicted flutter is an exponential-divergent type instability, which is called ‘hard’ flutter, since the vibration amplitude suddenly increases to infinity beyond linear flutter boundary [2,3]. Experimental and numerical evidences suggest that the aerodynamic nonlinearity under large amplitude will introduce a secondary stabilizing effect and the flutter performance manifests as a soft-type nonlinear flutter instability [2,3,4,5,6,7,8,9,10,11,12,13,14]. The occurrence of flutter instability is strictly prohibited by the Sensors 2020, 20, 568; doi:10.3390/s20020568 www.mdpi.com/journal/sensors

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