We have been working on improving inspections, aiming to make them more reliable and save labor, and these improvements have already been implemented. The hanger ropes of suspension bridges are important members that hang stiffening girders on the main cable. Excluding the Kurushima-Kaikyo Bridges, the hanger ropes used for suspension bridges use painted steel strands, and it was necessary to temporarily remove and disassemble the rope in order to check for corrosion inside the rope.
Therefore, we developed the "Total Magnetic Flux Method," a non-destructive inspection technology by which the decrease in cross-section area due to corrosion can be better estimated by measuring the number of lines of magnetic force present when the rope is strongly magnetized and comparing them to a sound area, which enables a reduction of the labor required for maintenance management.
In the steel deck, which directly bears the load of vehicles, fatigue cracks may occur due to the repeated load.
Early detection is important because these cracks lead to serious damage that affects the load-carrying capacity of the bridge. However, cracks in steel material covered with paint are difficult to discover through visual inspection from a distance.
Therefore, using infrared thermography, we developed a non-destructive inspection method using the phenomenon in which heat transmitted from the road surface is cut off in areas where there are cracks (temperature gap).
Fatigue crack non-destructive inspection (temperature gap method)
In accordance with the PDCA cycle (Plan → Do (Execution) → Check (Evaluation) → Action (Improvement)), inspection and repair results accumulate in a unified system; this is utilized as a database, leading to the implementation of more efficient management.
Inspection and repair information management system (JB IRIS)
The inspection and repair information management system (JB IRIS) registers maintenance data and repair data for structures such as bridges, tunnels, culverts, slopes, etc. into a unified system, and we are striving for safe and comfortable maintenance management of the Honshu-Shikoku expressways by utilizing this system to create repair plans based on judgments made on the structures' soundness and their inspection results.
PDCA cycle in inspection management work
Pavement Management System (JBPMS)
The pavement management system (JBPMS) registers pavement road surface configuration data, inspection data, and repair data into a unified system; along with evaluating the pavement's current conditions (pavement maintenance rate), we make estimations of pavement deterioration based on these data, and we are striving for safe and comfortable maintenance management of the Honshu-Shikoku expressways through the establishment of repair and investment plans.
Pavement Management System (JBPMS)
For the HSBE Bridge Project, we have developed and adopted a new painting specification, focusing on ensuring corrosion protection performance and long-term durability from the time of construction, using an inorganic zinc-rich paint with protective corrosion prevention for base coat and paint excelling in weather resistance (UV light protection) for finish coating.
As it is necessary to extend repainting cycles for reduction of repainting cost, it is desirable to develop more durable coating system or coating materials.
Estimation on the wear of coating vary by weatherproof performance of the surface paint, which is also critical for determining the repainting cycles.
We therefore developed high-durability fluorine resin paint (finish coating) to focusing on the loss of gloss leading to coating deterioration. The paint has been used in repainting on the Seto-Ohashi Bridge since 2011.
