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123456789_123456789_1123456789Case Study and Research
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Suspension Bridge Aerodynamics and Active Vibration Control

Truc Huynh, PhD


Suspension Bridge 

Model Examples

Model description


Geometry model

Analysis model

Landscape model

ICDAS Basis of Design


Additional features

Rendering & Animation 

Case Study and 

Trial Version


1. Introduction

The Tacoma Narrows Bridge failure in 1940, although it

was not the first bridge to be destroyed by wind, gave

rise to serious initial research on aerodynamic stability

of suspension bridges..


This research is a part of the above PhD emphasized
the following issues


- Natural Mode shapes and Frequencies

- Wind Loads on Bridges and Flutter

- Suspension Bridge Flutter for Girder with Separate 

  Control Flaps

Buffeting Response of Suspension Bridge

2. Natural Mode shapes and Frequencies

The natural mode shapes and frequencies of
suspension bridges are the first items to be computed
in design and analysis of the aerodynamics of
suspension bridges.

The following notations of the bridge mode shapes are 


SV  : Symmetric vertical mode

ST  : Symmetric torsional mode

ASV : Asymmetric vertical mode

AST : Asymmetric torsional mode

The key input to configure a suspension bridge using FEM
is the cable sag fm in the main span centre and the cable
sag fs (vertical) in the side span centre. The relation
between fm and fs can be approximately obtained by eq.

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Figure: Principle of deck girder with separate control flaps, [00,0]


Hm and Hs are the cable horizontal

forces (one) of the main span cable

and the side span cable, respectively.

Lm and Ls are the lengths of the main

 span and the side span, respectively.

mg is the girder mass and mc is the

cable mass (one), assumed to be to

equal in the main span and the side



Once the final configuration of the
suspension bridge is obtained through
iteration, the natural mode shapes
and frequencies can be performed.

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123456789_123456789_1123456789When the total horizontal cable force is acting on a single
joint at the pylon top, the longitudinal movement of the
pylon top (the flexural stiffness of each pylon leg) will
have influence on the torsional modes of the bridge.

In the ST mode, one main span cable vibrates downwards
and its corresponding pylon tops vibrate towards each
other in longitudinal direction due to the cable inextensibility
 in the quasi-static state. In the contract, the other main
span cable vibrates upwards and its corresponding pylon
tops vibrate away from each other, Figure 2.5


The increased constraining effects of the pylons of the

bridge in ST modes can increase the torsional frequency

considerably and indicate a more stable system.

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123456789_123456789_1123456789A numerical example for suspension bridge span 1000+2500+1000m is employed, with and without active vibration control.
The Akashi Kaikyo Bridge and the Great Belt Bridge are investigated for the key data of the example, Figure 2.2 to Figure 2.4.

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ICDAS  •  Hans Erik Nielsens Vej 3  •  DK-3650 Ølstykke  •   
E-mail: th@icdas.dk   •  Tel.: +45 29 90 92 96  •  CVR no.: 34436169