Wind Tunnel Testing of Bridge Decks

Abstract

The studies done in this thesis was connected to an early stage implementation of a new test method for ?nding aerodynamic properties of bridge deck sections at the Norwegian University of Science and Technology (NTNU), Department of Structural Engineering. This method is based on wind tunnel measurements of cross sections using a forced vibration principle where the bridge motion is forced by a custom made test rig. The rig performing the forced vibration tests is the ?rst of its kind at NTNU, and can produce motion in three degrees of freedom (horizontal, vertical and rotational), both separately and simultaneously. The forced vibration method is gaining popularity as it introduces a variety of possibilities in terms of aerodynamic testing.

The main goal of these studies was to develop a process of building bridge section models compatible with the forced vibration test rig and suited for early stage testing of cross section design. Furthermore, it was an objective to do wind tunnel testing of the crafted section models, and to analyze the output from the testing in terms of data quality and aerodynamic properties. The objectives were pursued in a four stage process. Theory studies and a series of calculations and material tests led to the design of two bridge sections strong and sti? enough to withstand the wind tunnel loading. The building process was performed at the department lab where all the design solutions were implemented. A series of forced vibration test were performed in the wind tunnel at NTNU, Department of Energy and Process Engineering (EPT), and the outputs from the tests were post processed and analyzed.

The work done resulted in a procedure of building models using the equipment available at the department and the materials found suitable. This includes a com- prehensive study of the individual material properties as well as the properties of the model as a whole. The possible designs of choice were thoroughly assessed, and this led to a choice of two section model concepts. A rectangular shaped section served as a reference model which was easy to build, while a Twin section became the main model of interest in this thesis. Aerodynamic properties of the models were extracted from data obtained by wind tunnel testing, and a quality assessment con- cerning the performance of the model was completed. Further, a comparing study of the results from the Twin section was performed with a similar bridge concept called Brusymfonien.

The section models developed in this thesis were found compatible with the forced vibration rig for the purpose of extracting aerodynamic properties. However, further work is required to increase the accuracy and achieve more stable results. Most important in this matter was shown to be the overall sti?ness of the models