|M.Sc Student||Frank Tal|
|Subject||Survey of Global Non-Destructive Testing of Reinforcement|
|Department||Department of Civil and Environmental Engineering||Supervisor||Dr. Yiska Goldfeld|
|Full Thesis text - in Hebrew|
Transportation structures like bridges, under passes, cantilevers etc. represent the key elements in terms of the safety and functionality of the entire transportation system. They are susceptible to combined action of environmental conditions (e.g., temperature, winds, rains, and humidity), service loads (e.g., railway loads, highway loads) and catastrophic events (e.g., earthquakes, floods, and vehicle collision). Therefore, maintaining structural safety becomes a challenging task and structural health monitoring (SHM) is essential to define the structure condition. In SHM, for existing and functional structures, the non-destructive method is the preferred method.
In the non-destructive method there are two separate ways to examine the structure condition. The first is the local method, which examines specific parts of the structure for damage or locations with high probability of damage, which needs to be evaluated. The second method is the global method, which aims at monitoring structural behavior in real-time. It enables evaluating structural performance under various loads and identifying structural damage or estimating its deterioration. Recent advances in sensing, data acquisition, computing, communication and data and information management greatly promoted the applications of global vibration based SHM technology in bridge structures.
The basic concept of vibration-based damage detection is that the dynamic characterization of the structure, notably natural frequencies, mode shapes, and modal damping, in addition to the structural mass, damping, and stiffness can be determined by measuring the deformation of the structure while it vibrates. Changes in the physical parameters like structural damages will cause detectable changes in the dynamic characterization. Due to the fact that the monitoring is mostly focused on finding the dynamic characteristics of the structure in addition to damage detection based on modal parameters, high precision of monitoring results is required.
Today, SHM has been extensively implemented in existing or newly built bridges in Europe, USA, Canada, Japan, Korea, China, and other countries. In Israel, local SHM method has been mainly performed on existing structures.
The purpose of this study is to classify the various dynamic tests applied in reinforced concrete bridges according to studies that were published at the open literature. The various methods of global non destructive tests over structures are divided into three main methods according to the characterization of the dynamic loads that can be applied on the structure. That is, ambient vibration tests, forced vibration tests and free vibration tests.
As part of this this study we aimed to explore the dynamic characteristics of simple concrete beam elements, that is used in bridges, by forced vibration test. The simulation of the forced vibration test has been done by a FE program MIDAS. In order to find the dynamic characteristics, the concrete beams were loaded by several dynamic loads (different frequency, amplitude and position). It was found that damage configurations, such as changing the boundary conditions or changing the modulus of elasticity, could be easily identified by frequency changes or mode shapes deflections changes. While other configurations of damage, such as reducing of the cross sectional area, could not be clearly identified by the method.