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How to inspect some of the oldest, tallest or most complex bridge structures in the world? We take a look at five of the most iconic bridges to see how they may be protected and inspected with different technologies
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According to the American Society of Civil Engineers, there are over 617,000 bridges across the United States, 42% of which are at least 50 years old and 7.5% of which are considered structurally deficient, meaning they are in “poor” condition. And this is only in the U.S!
Globally, the situation varies, but all countries have one thing in common – aging infrastructure!
Check out the five of the most iconic bridges around the world and how they may be protected and inspected with different technologies...
The Golden Gate Bridge, built in 1937, is a magnificent suspension bridge connecting San Francisco to the Pacific Ocean. The 894,500-ton bridge was designed and created in just four years and is considered to be an engineering wonder due to its complex engineering design and construction. The steel bridge is suspended by two primary cables passing over the tops of the towers and are fixed into concrete anchorages at each end.
The American Association of State Highway and Transportation Officials (AASHTO) recommends that a bridge must be inspected every two years. As reported in the San Francisco Chronicle, discussing the Golden Gate bridge inspection report 2018, licensed engineers and inspectors “scaled the length of the 81-year-old bridge's towers and concrete foundation, taking photos and scribbling notes on paper during the inspection over the course of three weeks.”
Fortunately, there are now more efficient ways to conduct visual inspections. Instead of using pad and paper to record findings, intelligent software like INSPECT can keep everything together, capturing defects with AI assistance, viewing them in AR and storing all inspection data, photos and notes together safely in one place.
The condition of the bridge's steel or concrete is not always visible and requires a multi-technology approach for testing structural health both above and below sea level. Below sea level are the large concrete foundations of the Golden Gate Bridge which support the two main towers. Inspection of these is done with specialist sonar equipment lowered deep under water as well as under water inspections with a dive team.
Above sea level, the iconic bridge consists of two steel towers and bridge deck, concrete piers, anchorages, and massive concrete blocks which hold the galvanized carbon steel wire supporting cables. The bridge deck can be scanned at highway speed with multichannel mobile mapping technology delivering 3D visualization in real.-time. The steel cables can be inspected with specialist metal hardness testers. The concrete blocks, piers and anchorages can be inspected using stepped frequency continuous wave ground penetrating radar (GPR), ultrasonic pulse echo, and rebound technology.
Powered by intelligent software, these non-destructive technologies can provide deep data insights into the condition, health and defects in the Golden Gate Bridge in real-time and give severity indicators for preventive maintenance decisions.
Tower Bridge is one of the UK´s most famous bridges, built back in 1886. The construction took a total of eight years to complete with more than 11,000 long tons of steel used for the towers and walkway framework, plus over 70,000 long tons of concrete for the two piers to support the structure. The framework was then clad in Cornish granite and Portland stone to protect the steel.
In the UK, bridges are required to undergo visual inspections every two years and a closer inspection every six years. Any concerning findings must be followed up with deeper inspections using specialist technologies to see into the stone or concrete and detect corrosion. We can see in an inspection report from March 2021 that in the last visual inspection for Tower Bridge there were no priority findings, some work required and some minor rust present.
This likely came as a relief after the extensive repairs and refurbishment the bridge has received over the years. During major repairs in 1991 and 1992, further corrosion was discovered leading to reinstatement of the structure as originally built, to restore the bridge´s strength and maintain its safety.
What´s difficult to see from the report is where exactly the rust is located and what the predictive maintenance timeline may be for the areas marked as ‘early signs of deterioration’ or ‘moderate defect/damage’, ‘some loss of functionality could be expected’.
But it doesn´t have to be guesswork. With software like INSPECT, not only can all findings be documented in a few clicks, but everything is also geolocated to the exact position. For structures that require regular inspections like the Tower Bridge, knowing exactly where the defects are can save hours of time for the next inspectors or maintenance team. Furthermore, INSPECT provides a single source of truth, with data from past and current inspections stored safely together. This avoids the common issue of data loss from paper reports or having several reports from different times all stored in different places. This can include not just the visual inspection data, but also the data from deeper inspections with various technologies.
Unlike the other bridges on this list, Tower Bridge is a combined bascule and suspension bridge which draws open to let ships pass through around 800 times per year. It also happens to be the largest drawbridge in the world. This means that inspections of Tower bridge, especially deeper inspections, can be a long and complicated process.
The base of each of the primary towers contains the hydraulics and counterweights for opening the 1200 ton bascules that make the roadway over the bridge. In 2021, these bascules failed to close after letting a ship pass through, leaving hundreds of motorists and pedestrians stranded at each end as they waited for it to be fixed. The high functionality of Tower Bridge combined with its age, requires a multi-technology, thorough approach to inspections to gain the full picture.
For example, to access, map and monitor the active corrosion in the concrete, advanced Half-Cell technology is an efficient solution. To test the concrete strength and uniformity, rebound technology, Ultrasonics Pulse Velocity and Ultrasound Pulse Echo work well as portable and accurate methods.
The durability of the concrete is also influenced by its water permeability. For structures like bridges that are located in and above water, checking the permeability can be an extremely valuable health indicator. To measure the permeability of the concrete on Tower bridge, a permeability tester can be used to give an accurate indication.
For the roadway, subsurface GPR can be used to access and map the road layer profile. The metal components can be inspected with specialist flaw detection technology and non-destructive hardness testers.
Data from the visual and multi-technology inspections can then be used to create an accurate timeline for predictive maintenance.
The Millau Viaduct in France is the world´s tallest viaduct bridge. Also one of the newest bridges in this roundup, the construction of Millau Viaduct started in 2001 and took just under four years to complete. Made from around 127,000 cubic metres of concrete, 19,000 tons of steel for reinforcing the concrete, plus 5,000 tons of pre-stressed steel for cables and shrouds, the builders of this multi-cable stayed bridge have claimed that the bridge should last for at least 120 years. The Millau features 7 concrete piers to support the four-lane motorway with hard shoulders, held in place with 154 steel cable stays.
Since the Millau Viaduct is one of the newer bridges, it’s also built with several technological features such as movement and motion sensors including accelerometers, anemometers, extensometers, and inclinometers. Due to its sheer height, these sensors help to locate potential points of issue or wear-and-tear that could shorten the bridge’s lifespan. Visual inspections for the Millau viaduct are usually conducted with a drone.
Another interesting point about this bridge is that it’s had detailed structural monitoring right from the beginning, providing valuable insights and data that older bridges don’t have. Since opening, it has had several detailed periodic inspections, plus annual inspections with specialist equipment in addition to the drones.
However, as we discussed in a recent interview with Marcel Poser, collecting vast amounts of data isn’t the end goal for inspections, especially when much of it could be classed as ‘bad’ or unusable data. The goal is to collect deep, informative, actionable data, preferably in real-time.
In the case of the Millau Viaduct, the sensors are critical for monitoring the bridge as it withstands tremendous seismic, climate and geographic challenges. This data is continuously monitored at the operations control room. Combining the structural monitoring with periodic inspections is a good example of using a multi technology approach to preventive maintenance. For a structure of this magnitude, extra care is needed to organize and manage the large quantities of data collected from all the different sensors and inspections.
As the Millau Viaduct has been monitored throughout its construction, the benchmark values were able to be established for future monitoring and maintenance. This shows the value and importance of recording all information and defects of a structure into a digital birth certificate. Furthermore, the viaduct also has specific provisions in place for preventive maintenance with all sides of the structure accessible.
The multi-cable stayed bridge is also equipped with sensors and devices for things like wind speed measurement, average air and deck temperatures, steel deck humidity, and detection of slippery phenomena. Other specialist technologies can be used to check the health condition, strength and integrity of the bridge’s concrete or steel.
Data from the drone, structural monitoring and inspections are all used together to accurately pinpoint any problems that require deeper inspections. For example, rebound technology can be used to check the concrete strength and uniformity of the piers in any questionable areas. Ultrasonics can be used to detect voids, honeycombing, or defects and one of the main strategies for inspecting bridges like this is combining ultrasonic pulse echo and GPR to monitor tendon duct health.
The Ponte Di Rialto bridge is a single span design by Antonio da Ponte, Swiss-born Venetian architect, and was completed in 1591 after three years of construction. It is the oldest bridge over the Grand Canal in Italy and has become one of the main attractions of Venice. The Rialto Bridge is made from Istrian stone, with two ramps boasting a row of quaint shops leading up to the central portico.
Over the centuries, the Ponte Di Rialto Bridge has received many inspections and restoration works. At the time of its build, many architects doubted the structure would last, but thanks to inspections, careful restoration and extra reinforcement, the bridge still stands strong. The most recent major restoration took place in 2015, treating all of the bridge´s structural components for the first time in over 400 years. The 364 columns showed fractures and were reset in molten lead for longevity. The preliminary survey showed no emergencies required special attention.
With intelligent inspection software, it´s possible to determine whether the surface condition findings in the visual survey are in the green (no action required), in the yellow (preventive maintenance needs to be planned), or in the red (emergency attention required). Any cracks can be identified and segmented with artificial intelligence and reports can be generated on the spot, building up a digital history of this famous structure.
During the restoration, workers were required to relay the gas, electric and telephone cables which powered the 24 shops on the ramps. When utility and power lines are buried under stone or concrete, ground penetrating radar (GPR) can be used to accurately locate them before any drilling or repairs. In particular, Stepped Frequency Continuous Wave GPR is most effective for achieving both depth and high-resolution object detection in real-time for this type of bridge.
To determine the homogeneity and strength, detect subsurface defects, or measuring the thickness, Ultrasound Pulse Echo is used as an effective solution, revealing valuable and historic data in augmented reality or heatmap displays.
The Sheikh Zayed Bridge in Abu Dhabi UAE is described as the world’s most complex bridge structure. Designed by the renowned female architect, Zaha Hadid, for the Abu Dhabi government, construction of the Sheikh Zayed Bridge started in 2003 and took seven years to complete. In total, the bridge is 842 meters long with 11 deck span sections, two four-lane roadways, an emergency lane and a pedestrian walkway. There are three major arches (the central arch reaches 63 meters high) with four main piers, plus two sets of supports. The Sheikh Zayed bridge (sometimes called the Hadid Bridge) is intended to be an iconic structure with an engineered lifespan of 120 years. Particular care was also reportedly given to ensure the bridge was built so there would be no weakness in the concrete that would allow corrosion to attack the steel reinforcement.
In the UAE and around the world, there has been a big shift in traditional bridge inspections over the past decade. For example, up until 2009, the Dubai Road and Transport Authority (RTA) used a paper and pen system for bridge or asset inspections and management. This cost considerable time for inspection engineers and made maintenance decisions more challenging.
As technology has moved on, bridge maintenance systems in the UAE are now mostly digital, and paper and pen has been swapped for the iPad or mobile for visual inspections. Now inspection data can be collected and reported easily from the location, no need to travel back to the office to compile everything, no risk of data loss. Furthermore, intelligent software like INSPECT can be used to create a 3D digital twin of the bridge to visualize it in its entirety with the accompanying findings from inspections and monitoring.
Many modern bridges are now constructed with built in sensors and imbedded corrosion monitors which, for large assets liken the Sheikh Zayed bridge, can help save time on visual inspections. However, physical visual inspections are also important, even for modern bridges.
The inspection engineer can take data from the monitors and use the information to assist with the visual inspection and pinpoint any problems. They can also capture high resolution images which are Geolocated on the map and stored securely with the rest of the asset’s records for post-inspection analysis. With INSPECT, the bridge can also be given a severity rating based on the findings so that decision makers have access to the right information at the right time. Advanced technologies are also utilized with just a few clicks on visual inspections using AI defect detection to identify and segment cracks on the concrete.
During construction, the Sheikh Zayed bridge had its own dedicated computer program to accurately predict the step-by step and long-term geometry changes. However, there are many components to this unique bridge that may still require deeper inspection. For example, the notorious arches of the Sheikh Zayed bridge were designed to resemble sand dunes to be fitting with the landscape but are not just for effect. They are bent box girders that are constructed of steel and linked together by blocks of concrete, reinforced with steel cables.
In total, almost 500 tons of high-quality concrete, 5000 tons of pre-stressed steel and 2000 tons of foundational steel were used. GPR is the most widely used and efficient technology for inspecting concrete and detecting what’s beneath the surface including defects and rebars. Detailed structural imaging with defect detection and determining the strength and homogeneity of the concrete can be done with ultrasonic pulse echo. Half-cell testing may also be used to check for chloride induced corrosion due to the close proximity of the sea water.
Other than being a signature structure of Abu Dhabi, the Sheikh Zayed bridge is an extremely functional bridge and is heavily used by vehicles with approximately 1600 cars passing through every single hour. With the 8 total lanes plus emergency lanes, road safety is a big priority. Checking the safety of every detail including the road markings is an important task.
With the bridge’s complex lighting system, ensuring good night and day visibility of the road markings can help save lives and protect the structure from accidents. The road marking visibility can be tested safely and efficiently with the use of dynamic retroreflectivity testers attached to a vehicle. This way, the road can remain open and there is no risk to the engineer performing the tests.
With so many types of bridge structures and various different technologies to inspect them, it has traditionally been a challenge to manage all the data from each source. Now, the data from all the various technologies, the reports, the drawings, photos and any other documents can be accessed from one secure Workspace. This is a breakthrough for bridge management, saving time and costs in both the short and long-term, and more importantly ensuring good health of the structure to prevent any disastrous events.
There is still a great need for awareness around preventive inspections around the globe. The technologies have changed dramatically to become user friendly, ergonomic, and even democratized so that it more accessible. Having digital inspection records and accessible reports of bridges health has proven invaluable for making preventive maintenance decisions before repairs become too much to manage.
To protect our built world and our global bridges, large and small, periodic inspections with the right equipment and preventive maintenance strategies are the only ways to achieving this colossal goal.
Want to see more how the technologies work to make bridge inspections more productive and cost effective? Check out how some of our customers are using INSPECT for visual inspections of large bridges and how GPR, ultrasonics and other technologies can be used for accurate and efficient concrete health checks.