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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 79
Edited by: B.H.V. Topping and C.A. Mota Soares
Paper 227

Semi-Active Fuzzy Logic Control of Suspension Bridge Flutter

S. Pourzeynali+ and T.K. Datta*

+Department of Civil Engineering, Engineering Faculty, The University of Guilan, Rasht, Iran
*Department of Civil Engineering, Indian Institute of Technology, New Delhi, India

Full Bibliographic Reference for this paper
S. Pourzeynali, T.K. Datta, "Semi-Active Fuzzy Logic Control of Suspension Bridge Flutter", in B.H.V. Topping, C.A. Mota Soares, (Editors), "Proceedings of the Seventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 227, 2004. doi:10.4203/ccp.79.227
Keywords: semi-active control, fuzzy logic controller, suspension bridge, flutter.

The long-span suspension bridges due to their large flexibility, lightness, and inherent low damping are much prone to aerodynamic flutter instability. Flutter is a wind-induced aerodynamic instability in the bridge deck at a critical wind velocity leading to an exponentially growing response. Flutter phenomenon, normally causes the catastrophic failure of the total bridge (Tacoma Narrows disaster, 1940).

The control of flutter by TMD systems has been studied by many researchers. Nobuto et al. [1], studied the effectiveness of the TMD control system on a sectional model of the bridge deck. Two TMDs were placed on the leading and trailing edge of the deck and their frequencies were tuned to resulting flutter frequency. The obtained improvement of the critical flutter wind speed was about 14%. Another TMD study is carried out by Pourzeynali and Datta [2], in which a combined vertical and torsional TMD system is applied to increase the critical flutter wind speed. The proposed TMD system has two degrees of freedom, which are tuned close to the frequencies corresponding to vertical and torsional symmetric modes of the bridge, which get coupled during flutter. The maximum improvement of the critical flutter wind speed is obtained about 2.03 times the uncontrolled flutter speed for 5% TMD damping ratio.

Wilde and Fujino [3] proposed an active aerodynamic control method of suppressing flutter of a very long-span bridge. The control system consists of additional control surfaces attached to the bridge deck, which are used to generate stabilizing aerodynamic forces.

Although in recent years, there have been many studies on the control of coupled flutter of long-span suspension bridges as reported above; most of them use passive control devices. Recently few studies are made on the active/ semi-active control of suspension bridge flutter. In particular, use of fuzzy rule base for semi- active control of suspension bridges is not reported before.

In this study, a semi-active tuned mass damper (STMD) system with variable damping is used to control the flutter instability of long span suspension bridges. For this purpose, a combined vertical and torsional model of tuned mass damper (TMD) system is used. This system has two degrees of freedom, which are tuned close to the frequencies corresponding to vertical and torsional symmetric modes of the bridge, which get coupled during flutter. The variable damping of the system is chosen through a fuzzy logic controller (FLC) system using the displacement and velocity at the center of the bridge, at which the TMD is placed, as the inputs. The transient response of the bridge due to a given initial condition in presence of the wind self-excited forces is controlled so that critical flutter wind speed for the bridge is enhanced.

The equation of motion of the suspension bridges is obtained by multi-mode finite element method in time domain using the energy approach and applying the Hamilton's principle. For this purpose, the entire bridge is discretized into two- dimensional beam elements, each consisting of two nodes at its ends. At each node four degrees of freedom are considered, in which in final equation the degrees of bending rotation and warping displacement are condensed out.

The methodology is applied to increase the flutter wind speed of the Thomas Suspension Bridge. Also, a numerical study is conducted to investigate the effectiveness of the semi-active control scheme, from which the following results are obtained:

  1. Semi-active TMD control system with variable damping is an effective method to control the flutter conditions of the suspension bridges.
  2. The proposed method is very effective in suppressing the transient response of the bridge within a few seconds.
  3. The rule-base matrix has the most significant influence on the proposed control system.

Nobuto, J., Fujino, Y., Ito, M., "A study on the effectiveness of TMD to suppress a coupled flutter of bridge deck", In J. struc. Mech. and Earthquake Engrg., Tokyo, Japan, No. 398/I-10, 413-416 (in Japanese), 1988.
Pourzeynali, S., Datta, T.K.,"Control of Flutter of Suspension Bridge Deck Using TMD", in International journal of Wind and Structures, Vol. 5, No. 5, 407-422, 2002.
Wilde, K., Fujino, Y., "Aerodynamic control of bridge deck flutter by active surfaces", in J. of Engrg. Mech., ASCE, 124(7), 718-727, 1998. doi:10.1061/(ASCE)0733-9399(1998)124:7(718)

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