A detailed assessment of the condition of an object.
The case study described here is related to the detection and monitoring of possible wire breaks. The capacity of the bridge is largely determined by the capacity of the stay-cables. The capacity of the stay-cables on their turn depends on the number of wires of the strands that are still intact. Regular inspection showed that, due to corrosion caused by rain, wires of the stay-cable can break and that wires have broken in the past. When multiple wires break, this affects the capacity of the strand. To ensure a sufficient capacity of the strands, frequent inspection of the strands takes place. This inspection is done visually, and is only done by examining the outer layer of the strands in the last three meters of the strand. On top of this, after detection of the first corrosion a climate chamber is built around the ends of the strands, thereby making it almost impossible for water to intrude. By keeping the water out, in combination with sustaining correct humidity and temperature, it is tried to prevent additional corrosion and thus additional wire breaks. In addition to the visual inspection also acoustic monitoring takes place. This monitoring system is installed in order to detect a wire break, based on the assumption that a wire break will lead to a high amount of (acoustic) energy in the strand. Apart from the acoustic monitoring system some additional measurements and monitoring has taken place in the past: 1) bypass are placed at a few strands. These bypasses consist of two clamping parts that are clamped onto the strand using bolts. Two steel bars are attached to this clamp and to the anchorage, thereby taking over a part of the force in the strand. The forces in these bolts, as well as the forces in the two steel bars, are continuously monitored. 2) force measurements are performed in the past, to determine the force in the stay-cables. To this end the taut-string method is applied. For those measurements the stay-cable is brought into vibration, and the vibration of the cable is measured using accelerometers. 3) multiple strain gauge measurement campaigns have taken place in the past.
Initiation of assessment
Required reliability check, Structural deterioration
Predominant verification type
Predominant verification scale
Ultimate limit state, Proxy limit state
Repair, Strengthening or upgrading