Award Date


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mathematical Sciences

First Committee Member

Zhonghai Ding

Second Committee Member

David Costa

Third Committee Member

Hossein Tehrani

Fourth Committee Member

Pushkin Kachroo

Number of Pages



It is well known that suspension bridges may display certain oscillations under external aerodynamic forces. Since the collapse of the Tacoma Narrows suspension bridge in 1940, suspension bridge models have been studied by many researchers. Based upon the fundamental nonlinearity in suspension bridges that the stays connecting the supporting cables and the roadbed resist expansion, but do not resist compression, new models describing oscillations in suspension bridges have been developed by Lazer and McKenna [Lazer and McKenna (1990)]. Except for a paper by Leiva [Leiva (2005)], there have been very few work on controls of the Lazer-McKenna suspension bridge models in the existing literature. In this dissertation, I use the Hilbert Uniqueness Method and the Leray-Schauder's degree theory to study two exact controllability problems of the Lazer-McKenna suspension bridge equation.

The first problem is to study the exact controllability of the single Lazer-McKenna suspension bridge equation with a locally distributed control. Unlike most of the existing literatures on exact controllability of nonlinear systems where the nonlinearity was always assumed to be C^1-smooth, the nonlinearity in the Lazer-McKenna suspension bridge equation is not C^1-smooth, which makes the exact controllability problem challenging to study. It is proved that the control system is exactly controllable. The key step is to establish an observability inequality of the auxiliary linear control problem. The proof of such an inequality relies on deriving a Carleman estimate.

The second problem studied in this dissertation is the exact controllability problem of the single Lazer-McKenna suspension bridge equation with a piezoelectric bending actuator. It is proved that the control system is exactly controllable when the location of the actuator is carefully chosen. The proof of exact controllability is based upon establishing an Ingham inequality for nonharmonic Fourier series.


Actuators; Bridge failures – Prevention; Control; PDEs; Oscillations; Piezoelectric devices; Suspension bridges


Civil Engineering | Mathematics | Transportation Engineering