Robotics allow inspection of cable bridges in ways inaccessible to manual inspection, helping improve their safety with prompt repair or replacement and also extend the span of their lives.
Cable Bridge Inspection With Robotics
Robotic technologies are able to rectify limitations of the manual cable inspection methods when it comes to cable bridges. Those are powerful nondestructive testing techniques such as include:
- Wire rope inspection that peers through the steel strands of bridges, monitoring for section loss caused by unplanned stresses and corrosion.
- Such inspection don’t require lane closures or bucket trucks.
- Robotic monitoring leads to fast interpretation and detailed, accurate and quantitative reports, locating even obscure broken wires.
“It’s really a very basic principle: Anything that you want to protect, whether it’s a car or a house, if you neglect it, you’ll likely pay a higher price later on.”
An astute observation by former Federal Liaison at New York State Department of Transportation, Antonio Estevez.
In fact, long years focusing on the country’s infrastructure made him realize a stark truth that is so often overlooked. “One of the lessons learned, from a history of neglecting our facilities, is that if you neglect a bridge, it will cost more in the end,” he said.
Indeed, bridges are expensive and vital national assets that require proper preventive maintenance for longer service life and to ensure public safety. In 1971, the Federal Highway Administration, in the National Bridge Inspection Standards, laid out minimum requirements for inspecting highway bridges. The main instrument to be used was visual inspection, which had to be done every two years. However, federal records indicate that a significant number of bridges go beyond the stipulated two years without safety inspections.
Manual v Robotic Inspection
In recent years, bridge engineering has advanced rapidly, making way for longer and more slender bridges, especially long-span, cable-supported bridges and cable suspension and cable-stayed bridges. The cable system of a bridge is considered an important subsystem which comprises main cables, stay cables and hanger ropes. The strength and durability of these ropes is vital for a safe and secure bridge. In fact, the cable rope is usually composed of high-strength carbon steel which is five to ten times stronger than regular structural steel.
As engineering firms engaged in maintaining bridge cables understand, only a few of the components such as high-density polyethylene (HDPE) cable sheathings, neoprene boots, and elastomeric rings, can be repaired.
Main Tension Elements (MTEs) near anchorages or in free spans which corrode or are fatigue-damaged, are irreparable. Even with no corrosion, excessive heat, or mechanical or chemical damage, a wire rope will fail in the area with the most amount of fatigue and abrasion. Thus, every steel wire rope is set to deteriorate and it will break during service if it is not monitored and taken out in time.
Therefore, preventative maintenance is essential to ensure the safety of cable systems.
Effective preventative maintenance that assesses material and structural conditions of cable systems, requires developing reliable inspection methods. Visual inspection methods that have been practiced through the years, and even today, have limitations, and therefore, are of dubious accuracy.
In the first instance, traditional inspection methods can be unsafe. Wire ropes in use in infrastructure could be seriously damaged, yet invisible to the naked eye, and therefore go undetected. Unanticipated wire breakages lead to unnecessary accidents and damage to life and property. In other instances, wire ropes are replaced on the assumption they are damaged. Subsequently, such impulsively replaced wire ropes have been found to have only slight defects or loss of strength. Thus, regular but needless replacement of wire ropes becomes a costly exercise.
According to German wire rope technology expert Roland Verreet, manual inspections can be unreliable because the rope may be inspected at the wrong locations or because the rope failed from the inside out.
In August 16, 2011, a fatal accident happened on an offshore oil production platform in the Gulf of Mexico region. Platform personnel were using the platform crane to move a generator from the platform on to a motor vessel. Two riggers were on deck, close to the load being hoisted. While the generator was being lifted, the crane’s boom hoist wire rope broke and the generator dropped to the deck, and the boom fell, hitting the generator. The boom broke into three sections. The boom nose fell, and dragged the 850-lb bridle/sheaves, striking and fatally injuring a rigger.
Investigation into the accident found that the crane’s boom hoist wire rope had weakened due to internal and external corrosion, loss of integrity, ductility and strength. There was advanced corrosion apparent in post-accident examination. However, the annual crane inspection carried out six months before the accident failed to identify the corrosion and reported the wire ropes were “OK.”
Overlooking serious signs of failing on wire ropes cannot be ruled out in visual inspections, because the naked eye can miss a lot of red flags.
Robotic Wire Rope Inspection
On the other hand, robotic technologies that have emerged in recent years such as those of Infrastructure Preservation Corp. are able to rectify limitations of the current cable inspection methods. Robotics technologies are generally associated with powerful nondestructive testing techniques for bridge cable systems that are inaccessible with manual inspection methods.
“IPC’s robotic wire rope inspection service inspects the entire cable and issues that are found can be addressed based on their severity,” says IPC President Doug Thaler. “Our robotic devices and services are wireless, light weight, portable and do not require lane closures or bucket trucks and most of all accurate.”
Wire rope inspections are a part of IPC’s CableScan services that provide quantitative condition assessment data to asset owners.
As Thaler describes, the wire rope inspection is done by peering through the steel strands, monitoring for section loss caused by unplanned stresses and corrosion.
Robotic monitoring leads to fast interpretation and detailed, accurate and quantitative reports, locating even obscure broken wires. Wire ropes being a blind spot in safety management, and always of concern in hoisting operations, can be handled without fear, once robotic wire rope inspections and cable assessments are done and reports give the green light.
Knowing when to replace your wire rope is a major boon to the construction industry, and to infrastructure, Thaler adds. What is required is a change in perspective, from relying on outdated visual inspections to transferring preference to modern technology. There is no comparison when it comes to safety of life and property.
It is timely to remember the words of American philosopher Wayne Dyer, who said, “If you change the way you look at things, the things you look at change.”