Cable-stayed bridges quantitative in-depth stay cable inspections

CableScan® is an innovative Nondestructive Testing (NDT) robotic inspection service that is rapidly improving how the inspection of stay cables on a cable-stayed bridge is performed with this much safer and more in-depth inspection. 

Prior to BVNA’s CableScan® service, traditionally rope-access climbers (inspectors) harness themselves to the bridge stay cable to perform a visual inspection of the exterior of the sheathing that surrounds the structural portion of the stay cable holding up the bridge deck – the strands. The sheathing surrounding the strands are typically either made of High-Density Polyethylene (HDPE) or are metallic in nature. The main purposes of the sheathing that surrounds the strands is to protect the strands from ultraviolet rays from the sun as well as to prevent moisture to penetrate the strands, which causes the strands to corrode or become damaged, thus reducing the structural capacity of the bridge. In randomly selected locations, cable wedging is performed to inspect the interior of the sheathing for possible deterioration or corrosion of the stay cable. Ironically, cable wedging allows for additional moisture to penetrate the sheathing, causing further corrosion and/or deterioration of what inspectors are trying to properly maintain. 

Prior to Bureau Veritas’ CableScan® service offering, many Asset Manager’s and bridge Owners were all asking the same exact question – “While a visual inspection of the exterior of the sheathing is helpful to detect “suspect” locations to perform wedging in select locations, how do we know we are capturing all locations where the strands are experiencing Loss of Metallic Area (LMA)?” 

That’s a great question asked by the industry, and Bureau Veritas is pleased to present a solution to ease the concerns of many bridge Owner’s through the use of CableScan®. As you can see in the video below, the CableScan® robot wraps around the exterior of the stay cable sheathing to wirelessly lower and climb each stay cable of the bridge. As CableScan® wirelessly climbs and lowers the free length of the HDPE stay cable, it performs two major functions: 

  • The equipment “peers through” the HDPE sheathing to the strands to perform Magnetic Flux Leakage (MFL) to detect and quantify the LMA within the strands; 

  • Performs a 360° Close Visual Inspection of the exterior of the sheathing using four (4) HD cameras mounted to the robot. – Exceeding the Close-Visual requirements of National Bridge Inventory (NBI), American Association of State Highway and Transportation Officials (AASHTO), and Federal Highway Administration (FHWA). Furthermore, the full-length video and still photographs of the entire inspection process are provided for permanent inspection records.

CableScan® allows for a real-time evaluation as both the MFL readings and the video feed of the 360° Close Visual Inspection are wirelessly transmitted to the inspection crew on the project site, allowing them to detect any anomalies detected while on the project site so that we may take a photograph of the suspect area detected.  

As a result of Bureau Veritas’ inspection, our Client receives the following deliverables that they require to be able to make the most educated decisions moving forward on how to properly protect their asset:  

  • A detailed and comprehensive inspection report including the location of all anomalies detected and the detected and quantified Loss of Metallic Area experienced by the strands; 

  • The full length HD video of the Close Visual Inspection performed on all stay cables; 

  • HD still photographs of any/all anomalies detected to the sheathing. 

If you are looking for a comprehensive, in-depth, quantitative, repeatable and cost-effective solution to perform the inspection of 100% of the stay cables on your signature bridge, you’ve come to the right place! 

Added benefits:  
  • No lane closures; 
  • No bucket trucks;  

  • No need to make this a nighttime inspection; 

  • No additional damage to stay cable sheathing from bucket trucks hitting them. 

Contact Robert Busch