Bridge Inspections For A Safer Infrastructure
The Advancement Of Bridge Crack Detection TechnologyNovember 16th, 2017 Author: Doug Thaler
Bridge crack detection utilizing nondestructive testing methods to date has been an unrealized and an unrealistic way to manage concrete and bridge assets globally.
The primary method of detecting bridge cracks is manually with an inspector physically looking at the bridge surface while dangling from a boom truck and measuring the crack with a caliper like device. Sketches in a notepad are then rendered by hand. There are many issues with this method. First it is subjective in nature and the results will vary from one inspector to another.
Additionally, the cost of manual inspections are high. Bridges typically go over waterways or highways, roads need to be closed while inspections are taking place. The department of transportation needs to be called out to direct traffic while the inspectors work. In many cases boom trucks need to be utilized to lift the inspector up to the bridge. This not only creates a huge expense but puts the inspector at risk.
For the purpose of maintaining the bridges and seeking out required repairs and timely decision making a physical inspection is just not an accurate inspection method. The use of more current technology like impedance based structural health monitoring, radar and electrical impedance were tested by the TRB (Transportation Research Board) and were also found not to work or to be practical for crack detection.
Crack detection methods to date all have their drawbacks. According to a study put out by the Transportation Research Board. All of the methods studied were either not possible in the field or not accurate enough to be viable. To quote see below taken from one of their papers.
“Discrete Crack Detection To find an alternative to the detection of individual cracks by visual inspection, a significant amount of effort has gone into development of automated analysis software for pattern recognition of cracks in digital images
When a crack is detected, it is then characterized by a set of parameters including location, length, width and direction (Mahler and Kharoufa, 1990). There are two major considerations in the sensitivity of this process: one is the probability of detection and the other is the probability of false positives. An algorithm with a low probability of detection will miss a significant number of cracks. An algorithm with a high number of false positives may detect a high percentage of actual cracks, but may also mistake other features for cracks.
After a crack has been detected and characterized, it may then be assigned to a particular class. The problem with diagnostic classifications is that more than one cause of damage may produce the same crack appearance. Microcrack Measurement Techniques Conventional methods for measuring microcracks include optical microscopy, scanning electron microscopy and radiography. These have been reviewed by Slate and Hover (1984).
They are all destructive, requiring the drilling of cores from the concrete followed by sectioning of the specimens, and the results are two-dimensional.
More recently three-dimensional methods using computed tomography based on conventional X-ray or synchrotron radiation have been introduced. These can image entire specimens. The true crack area can be measured, rather than its two-dimensional projection. However, the overall size of the specimen is limited to less than 100 mm (4 in.) in thickness for useful resolution.
Moreover, these cannot be applied in the field.
Ultrasonics Other methods for measuring microcracks are based on ultrasonics (Kesner et al., 1998; Jacobs and Whitcomb, 1997). These methods do not count individual cracks, but rather measure a bulk ultrasonic property of the concrete, usually attenuation. This can then be calibrated against radiographs to give microcrack density (Kesner et al., 1998). Ultrasonic methods offer the possibility of making measurements in the field on real structures.
Their drawback is that features other than microcracks in the concrete can contribute to attenuation. Acoustic Emission Acoustic emission describes a field of testing that has been popular recently in crack detection because of its non-invasive nature (Ouyang and Shah, 1991; Ohtsu, 1994; Ohtsu, 1996). Recent research has indicated that it is possible to quantify cracking using acoustic emission. The sensors detect acoustic activity when the specimen undergoes cracking, and they are amplified.”
IPC (Infrastructure Preservation Corporation), Clearwater Florida has created the solution to Bridge Crack Detection and Bridge Crack Measurements including progression analysis over years, with IPC’s Bridge Crack Measurement Service.
IPC is able to detect and measure concrete cracks down to .005mm and works from a distance of 1000 feet.
What does this mean for the industry?
It means that bridge inspections needing a bridge crack analysis and bridge crack progression monitoring can now be quantitative in nature with real results being transmitted to a laptop. Results are recorded to determine not only current issues in a bridge but map the bridge deterioration and crack progression over time.
IPC can map the actual location of the crack, the length and the width of a current crack. Cracks can be overlayed on a 3d CAD image of the asset to better determine the urgency of attention required by the asset manager. IPC does this utilizing Non destructive testing methods with no lane closures, boom trucks or additional expenses incurred for the engineering firm or the Department Of Transportation. In fact IPC’s Concrete Crack Testing Service and save 35% or more during one inspection cycle.
The value of having the bridge progression analysis over many years can save millions in knowing how severe an assets deterioration is how quickly the progression of deterioration is occurring and help in budgeting its maintenance and repair schedule.
For more information on IPCs bridge crack detection system contact [email protected] IPC is leading the way in creating new nondestructive testing methods that can create condition assessment reports to help manage infrastructure assets worldwide.