Ouput-only vibration analysis of buildings in operational conditions

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Currently, owing to advances in sensing techniques and analysing procedures, the most popular experimental modal test for large structures is ambient vibration testing. Ambient vibration analysis leads to the essential structural characteristic of buildings called modal properties: mode shapes, natural frequencies and damping ratios. These information are essential to keep track of future changes in the integrity of a structure, serve as its baseline and help monitoring health of structures. Ambient vibration test is performed during normal operation of the structure, therefore there are different source of vibrations: wind, micro-tremors, human activities. Existence of these numbers of vibration sources requires very careful analysis of the recorded weak signals to be able to accurately derive modal properties. Current existing frequency and time domain methods have shortcomings with regard to analysis of noisy signals, closely space modes and damping ratios. They are complex to be used by engineers, and also their advantages and disadvantages are not clearly specified. The goal of the proposed project is to develop a new mix frequency / time domain method to improve the modal identification process. The goals of this project are summarized as follow: i) Detailed literature review of exiting methods to clearly identify their pros and cons. ii) To develop new algorithm that can deal with ambient signals with higher noise, allowing to use less sensitive low-cost sensors. iii) The developed algorithm should be able to handle the closely-spaced modes more efficiently. iv) To develop a simple method for on-site verification of time records so that the technician can re-conduct the test if a problem is detected. This technology transfer is essential for Sensequake Company and engineering community around the world.