Portland State University. Department of Civil & Environmental Engineering
Date of Award
Doctor of Philosophy (Ph.D.) in Civil & Environmental Engineering
Civil and Environmental Engineering
1 online resource (xii, 125 pages)
Nondestructive testing, Structural health monitoring, Reinforced concrete construction -- Testing, Frequency response (Dynamics)
Concrete is widely used for civil infrastructure structures and they experience deterioration and degradation due to aging, increases in the traffic loads, harsher environmental conditions, use of deicing chemicals, etc. Therefore, evaluating the integrity of reinforced concrete structures has become of increasing interest for infrastructure owners and managers. A number of non-destructive testing (NDT) and structural health monitoring (SHM) methods have been developed in recent decades to aid in evaluating structures and provide input for asset management. One family of these methods uses the dynamic response of a structural member: stress waves (high frequency) and structural vibrations (low frequency). Both the high and low dynamic response frequencies were studied in this PhD dissertation for NDT and SHM purposes resulting in three novel tools.
First, an ultrasonic coda wave comparison (CWC) method was developed, which is a new method to monitor stresses in reinforced concrete members. An ultrasonic wave, representing the high frequency dynamic response (stress wave), was used in this method. Magnitude-squared coherence (MSC) was used to estimate the similarity between two recorded ultrasonic waveforms: a reference waveform under initial stress and one taken at a certain level of applied stress. Through a series of laboratory experiments and an in-service bridge test, the method was found capable of capturing minute changes in the internal stresses in a concrete member.
Second, the modal parameters of the structural vibration response (low frequency) of a reinforced concrete girder was investigated as a means to detect service-level flexural cracking. In addition, this investigation emphasized the important effects of elastic support conditions on the modal parameters. The experimental testing of a large-scale reinforced concrete girder suggests that elastic supports have a significant effect on modal parameters. Also, natural frequencies of higher modes (higher that three) can be used to detect flexural cracks, unlike the natural frequency of the first and second modes that might give a wrong indication of cracking.
Finally, a nonlinear vibration index (NVI) method is proposed to detect degradation and delaminations in a reinforced concrete bridge deck. The novelty of this method is that it is reference-free, i.e. no measurements from the undamaged state are required. The approach was simulated numerically using a finite element model and evaluated on an in-service concrete bridge deck. The results show that the proposed NVI method has the ability to detect degradation and delaminations. The availability of visual inspection data, concrete cores, and depth of removed concrete from ultra-high-pressure hydro-blasting provided further confirmation of the method.
Hafiz, Ali, "Evaluation of Low and High Frequency Dynamic Response for Condition Assessment of Reinforced Concrete Structures" (2019). Dissertations and Theses. Paper 5122.
Available for download on Friday, August 14, 2020