Structural dynamic response of the Glass Truss Bridge
E.M. de Vries Robbé (TU Delft - Civil Engineering & Geosciences)
R. Nijsse – Mentor (TU Delft - Applied Mechanics)
Alessandro Cabboi – Graduation committee member (TU Delft - Offshore Engineering)
F. Messali – Graduation committee member (TU Delft - Applied Mechanics)
Pieter Schoutens – Graduation committee member (Witteveen+Bos)
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Abstract
Bridges are exposed to dynamic forces – such as pedestrians crossing a bridge or the wind force acting on a bridge – which cause vibration of the structure. When a structure is forced at one of its eigenfrequencies it deforms into a corresponding shape leading to major deformations, which, in the worst-case scenario, can lead to collapse of the structure, as happened to the Tacoma Narrows bridge in 1940. It is thus very important to know the dynamic characteristics of a structure. For glass structures no specific limit values are defined, this is why it is interesting to investigate the dynamic behaviour of a glass bridge This thesis aims to predict the structural response of TU Delft’s Glass Truss Bridge when subjected to static and dynamic loads. The studied bridge is a footbridge, connecting the TU Delft campus to the Green Village, and is unique in the aspect that glass diagonals have been used in its construction. Through an iterative procedure of modeling, virtual testing and updating the model of the bridge, the dynamic response of the bridge is predicted. The study shows that the response of the bridge is between the European Guidelines’ limits for (steel) footbridges. Maximum acceleration of the bridge is found at 500mm/s and the lowest eigenfrequency is out of range of that of joggers. The sensitivity analysis shows that the parameters having the most influence on the bridge’s response are the diameter of the glass diagonals and the soil density. Using the outcome of the sensitivity analysis a dynamic testing protocol is recommended that outlines the optimal test setup for modal testing of the bridge. Through the simulated dynamic tests ten of the twenty eigenfrequencies of the bridge are found. For each of these frequencies, the damping is approach and modeshapes are reconstructed based on the imaginary plots of the Frequency Response Functions. The latter show a good correlation with the modeshapes obtained from the model.