What is the most reliable and appropriate method for evaluating a structure? Well, that is the question we have been facing a lot lately. Clients ask for the affordable, yet precise methods to evaluate the safety and reliability of their capital intensive assets. In order to understand the situation, one needs to understand the economy of the structure under investigation, that is how far our inspection and evaluation methods can intervene with the operation of the structure. For example:
+ How long can we stop the traffic on a major highway? and How it would affect public?
+ How long can we halt the operation of a refinery?
+ What are the limits and restriction when implementing a specific monitoring system?
Another aspect of the economy of condition assessment is the actual value for the client? In technical aspects, our existing test methods might be good enough; however, choosing the right methods that are also financially acceptable for the client remain a huge challenge.
Why Non-Destructive Evaluation
There is a big demand for detecting and characterizing deterioration in bridges. Necessary steps should be taken to retrofit, rehabilitate or sometimes demolish the current infrastructures. Non-destructive evaluation can be used for condition assessment of existing structures. Non-destructive methods are suitable because:
+ They reduce the number of intrusive tests
+ They are generally fast, and repeatable, making them ideal for routine inspection
+ They can predict structural properties with good precision.
The Curious Case of Bridge Structures
Developing and implementing the means for quick and reliable inspection, rapid rehabilitation/retrofit, and performance monitoring of highway bridges is imperative for two reasons:
+ To detect the deterioration during its early stages and to mitigate proper remedies
+ To reduce the traffic interruption while adhering to get in-get out- stay out motto.
The traditional approach for condition assessment of bridge decks has been visual inspection in conjunction with chain dragging and hammer sounding which are very subjective and operator-dependent. Moreover, these methods are unable to detect early stages of delamination and are for all practical purposes, ineffective where the deck is overlaid with asphalt.
The traditional methods provide subjective results that are then used to define the scope of work for rehabilitation of the bridge. It should be clear that planning the rehabilitation or replacement of a bridge based on this subjective information does not facilitate the optimal allocation of resources and can result in costly overruns during construction. This points squarely to the need for a means of obtaining an objective, accurate assessment of the bridge deck inventory.
The Second Strategic Highway Research Program (SHRP 2) has identified various NDE techniques for condition assessment of bridge decks. The report ranks these methods based on their effectiveness in detection and characterization of four major deterioration types: delamination, concrete degradation, reinforcement corrosion, and vertical cracking. SHRP 2 recommends the use of ground penetrating radar (GPR), impact echo (IE), ultrasonic surface waves (USW), half-cell potential (HCP), electrical resistivity (ER), and chain drag/hammer sounding for bridge deck evaluation. Click here to read more
Finally, it is very important to understand that by using NDT techniques, repairs are completed faster, more safely, and with minimal impact on motorists. Moreover, it can shorten period of rehabilitation. We need a strong attention and education to make infrastructures safer.
About the Author
Arezoo is a Civil / Mechanical Engineer with an interdisciplinary background specializing in nondestructive evaluation of reinforced concrete structures and pavements. She has been involved in a number of high profile NDE research projects funded by FHWA, NIST, and NAS. She has coauthored the FHWA SHRP 2 report for NDE condition assessment of RC bridge decks (PDF – Read More). Arezoo has worked in construction industry for OHL USA as a Quality Control Engineer on a grade separation project in Anaheim, California (Learn more). She is a PhD candidate at Rutgers University working on GPR evaluation of bridge decks.