ABSTRACT
The Ha’penny Footbridge is a historic cast iron structure in Dublin City Centre and a well-known Irish landmark. The main objective of this research was to establish a comprehensive picture of the dynamic behaviour of the bridge. This information and the associated model could then be used in future structural health monitoring (SHM) and damage detection, with the aim to aid in the structure’s preservation and prolong its serviceability. The methodology of this study began with the creation of a preliminary finite element (FE) model using the computational software MATLAB (The MathWorks Inc). This model was designed to assess the free-vibrational response of the structure in three dimensions from first principles, including its natural frequencies and mode shapes. The modes obtained from this preliminary analysis were then used to assist an operational modal analysis (OMA), carried out using strain gauges fitted to the structure. The results of this analysis were used in order to update and calibrate the FE model. The result of this research and experimentation was an accurate representation of the bridge within acceptable limits. The FE model developed using MATLAB was found to have improved accuracy when compared to a previous model created using a FE software package in 2001. The calculated damping ratios of the structure were found to be low and so the installation of a permanent SHM system was recommended. In addition, it was recommended that the structure be fitted with an increased number of strain gauges to allow for strain measurements to be gathered in multiple directions.
