As I was saying, my research interests and expertise meet this challenge by creating innovative solutions in two main streams through efficient use of advanced materials and proper implementation of new technologies:
1. Enhancement of Existing Bridges:
Bridges are designed and built to be safe against failure, and to perform satisfactorily during their service life. Over the past few decades, however, they have been deteriorating at an alarming rate due to aging, inadequate maintenance, adverse environmental conditions, and constantly growing transportation demand. Deterioration of bridge infrastructure has recently become a global concern. I address this concern by conducting research studies on the enhancement of the structural performance of in-service bridges through a two-phase plan:
1.1 Phase I – Structural Evaluation and Damage Identification:
In the first phase, I focus primarily on the structural evaluation of the bridges through innovative damage identification techniques (DITs). Implementation of robust DITs is essential for detection of any distress in bridges at the earliest possible time. Implementation of a DIT is referred to as a Structural Health Monitoring (SHM) process. The basic assumption in SHM is that damage changes the dynamic response of bridges. However, one major concern with the structural evaluation of the existing bridges is that information on their response at a reference (undamaged) state is not available for comparison with the response measured at a current (damaged) state in order to determine the damage-induced changes. Therefore, a DIT that does not require a prior knowledge of the reference state of bridges is needed.
I have been working on the development of an innovative reference-free DIT that can overcome the above mentioned difficulties associated with damage identification in the existing bridges. The DIT performs relative wavelet entropy (RWE) analysis on the vibrational signals measured only from current state of bridges. The signals must be obtained at multiple locations on the bridges’ structural components that theoretically correspond to a similar dynamic response. Since structural damage imposes changes in the responses obtained at damaged locations compared to undamaged locations, quantifying this dissimilarity through the RWE analysis can identify the targeted damage.
1.2 Phase II – Strengthening and Rehabilitation:
In the second phase, I use the results of Phase I in order to design efficient strengthening systems for damaged bridges to enhance their structural performance and to protect them against further deterioration. However, utilizing only conventional materials, such as concrete and steel, leads to increased self-weight of the bridges and only decreases the rate of corrosion, but does not prevent it. Therefore, I carry out research on application of advanced composite materials, such as fiber-reinforced polymers (FRPs), for strengthening and rehabilitating the damaged bridges. In addition to being corrosion-resistant, FRPs have high strength to weight ratio, are easy to handle, enhance durability, and reduce maintenance costs.
2. Development of Future Bridges:
Rapid growth of urban population and economy requires the development of smart transportation infrastructure, which is sustainable and resilient. I contribute to this objective through working on the development of smart bridges. In my research, the notion of smart bridges refers to the bridges that are designed based on innovative structural solutions and constructed using advanced composite materials. They also utilize state-of-the-art technologies for SHM purposes in order to enhance the public safety.
2.1 Phase I – Hybrid Structural Systems:
Although applications of FRPs in strengthening of existing structures have been promising, utilizing them as load-carrying elements in new structures has been limited due to their low rigidity. Nevertheless, I have eliminated this restriction in my conducted research by adopting a hybrid approach, in which a conventional material, such as concrete, is combined with a composite material, such as glass-FRP (GFRP), to form a hybrid system. In this hybrid structural system, the conventional material provides stability and rigidity while the composite material enhances strength, ductility, and durability.
Throughout my graduate studies, I have conducted an experimental research study on concrete-filled FRP tube (CFFT) systems. I studied the effects of different parameters on the axial strength of the CFFT elements and the strength of the developed bond between the concrete core and the FRP tube. I was also successful in increasing both axial and bond strengths of the CFFT elements by adding an expansive agent in the concrete mix. This innovative idea also enhanced the structural integrity of this hybrid structural system.
Therefore, the application of hybrid FRP-concrete structural systems in the development of future bridges is of great interest for me. In particular, I have been conducting a comprehensive research on development of an innovative hybrid FRP-concrete bridge truss girder system, which was designed by Dr. Mamdouh El-Badry at the University of Calgary in 2002. The girder system consists of pretensioned top and bottom concrete chords connected by CFFTs. The concrete chords are reinforced with GFRP longitudinal bars and transverse stirrups. The CFFTs are reinforced and connected to the chords by means of long double-headed GFRP bars. The deck slab is connected to the girder’s top chord by means of double-headed GFRP studs. This innovative girder system is lighter in weight and more durable than the conventional I-girders. It can also pass flooding through its hollow web. Hence, it significantly contributes to the objective of developing more sustainable and resilient infrastructure. Building on my previous experience, I plan to expand my research in this area by developing innovative hybrid structural systems to meet our desires for smart bridges.
2.1 Phase II – Smart Structural Health Monitoring (SSHM):
The performance of bridges can be affected by various types of damage caused by excessive loading and extreme events. Therefore, SHM has become essential to enable making decisions on the necessary measures for maintenance and/or repair in order to ensure both safety and serviceability over the life of infrastructure facilities.
I plan to expand my research in the field of SHM by developing a smart SHM (SSHM) system to overcome shortcomings of current systems. The SSHM system will utilize a state-of-the-art sensing system consisting of a variety of sensors, including but not limited to, accelerometers, temperature and humidity sensors, strain gauges, load cells, cameras, and fiber optics. The sensors will be connected to a server through a wireless network and communicate with each other using a platform built upon Internet of Things (IoT) concept. The required power for the system will be supplied by the energy harvested from the traffic-induced vibrations of the bridge using piezoelectric energy harvesters. Therefore, the proposed SSHM system will utilize the bridge’s daily traffic-induced vibrations to monitor the bridge performance and to provide the energy required for the monitoring process. The SSHM will not interrupt the bridge’s normal operation and is applicable even if no data are available from a reference state of the bridge. The undesirable effects of varying operational and environmental conditions of the bridges on the identification of the targeted damage will also be mitigated as the SSHM utilizes an advanced signal processing techniques formerly used in the quantitative analysis of brain electrical signals.