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Title:Damage assessment in reinforced concrete using contactless ultrasound
Author(s):Ham, Su Yun
Director of Research:Popovics, John S.
Doctoral Committee Chair(s):Popovics, John S.
Doctoral Committee Member(s):Weaver, Richard L.; Lange, David A.; Oelze, Michael L.; Rydén, Nils
Department / Program:Civil & Environmental Engineering
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):ultrasonic
concrete
Abstract:The poor state of the deteriorating national infrastructure makes essential the need for implementation of non-destructive evaluation (NDE) and structural health monitoring (SHM) for existing concrete structures. Conventional contact-type ultrasonic testing (UT) methods offer efficient and useful approaches to characterize internal defects in concrete structures in a nondestructive fashion. However, the large testing areas normally associated with concrete structures make conventional ultrasonic methods extremely labor- and time-intensive. Contactless, or air-coupled, UT systems offer a solution to this limitation. In this thesis, high-performance contactless UT systems are studied, developed, implemented and verified in order to characterize several different type of damage (delamination, distributed microcracking, and rail seat deterioration) in concrete structures. The work comprises new hardware system design and testing approach development. The hardware, comprising the modified sensors and the automation/robotic scanning system, are designed and assembled by the author. The performance of the system is optimized with respect to generated pulse frequency content and energy, signal to noise ratio, and rapid data collection and scanning. Dynamic finite element method (FEM or FE) simulations of mechanical wave-based NDE methods are developed and described in order to support the system construction, theory verification, and experimental work. The FE models simulate generation and detection of air-coupled transient waves in air and wave interactions at the interface between concrete and air from internal defects and random scatterers. Next, three NDE applications with different types of damage are reported. New experimental and analytical approaches are introduced and deployed for each case, where the fully contactless UT system is used for each. The first study deploys multichannel analysis of surface waves (MASW) measurements interpreted through Lamb wave mode analysis; 3-D images are generated that make use of the Lamb wave mode jump condition in order to identify the presence of underlying delamination defects. The next application incorporates ultrasonic backscatter measurements to characterize distributed microcracking damage in concrete. Two different backscatter measurement schemes – time domain energy subtraction analysis (ESA) and spectral variance analysis (SVA) – are developed and applied through numerical simulation and experiment. The experiments are deployed using concrete samples containing well controlled artificial damage and imparted cracking damage. Both coherent and incoherent wave analyses are performed to study scatter characteristics. The backscatter energy measurements are sensitive to the presence of distributed microcracks as compared with conventional UT approaches. Also backscatter approaches provide statistically significant distinctions between damage levels in concrete. The collected backscatter data are also applied to image and identify localized regions of damage. In the third application, surface waves are used to interrogate interfacial damage related to rail seat deterioration (RSD) in concrete rail ties. Results from the UT tests on concrete tie samples are reported, where experimental results provide clear distinction among different RSD levels. Close proximity and large-offset scan configurations, which is appropriate for application to rail structures in situ, are proposed. Finally, future efforts toward additional implementation to actual bridge, nuclear power plant, and rail-field tests are proposed based on the work reported here.
Issue Date:2015-11-19
Type:Thesis
URI:http://hdl.handle.net/2142/89196
Rights Information:Copyright 2015 Su Yun Ham
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12


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