NDT for need based maintenance of bridge cables, ropes and pre-stressed elements

Abstract

This has given life cycle management of infrastructure an increasingly important role. Reliable inspection and monitoring tools are therefore in demand. A reliable prognosis of the condition and behaviour of a structure is an important basis for an effective service life management. Furthermore, traffic loads and loads due to changing environmental conditions increased during the last years and will increase in the future. Repair and maintenance have to be performed, which requires reliable concepts and measurement of data, which is preferably gained through non-destructive methods. Furthermore, infrastructural constructions often have to be reconditioned when they are in use i. e. they cannot be torn down and rebuilt. Therefore, reliable diagnosis of the state of 'hot spots' is required. Within the frame of the Franco-German project FilameNDT steel wires of external tendon ducts and prestressing strands, prestressing rods, and stay cables are investigated. With regards to this field of application, practical relevance can only be gained when easily applicable and long ranging methods are used. The evaluation of extended structural elements using non-contact movable systems {bulk wave and guided wave application [Piezo, electromagnetic acoustic transducers (EMAT)], magnetic flux leakage (MFL), Micromagnetic methods} and those of localized elements based on elastic guided wave propagation are complementary since they can be applied according to the various accessibility conditions of the tested objects. Inspection and monitoring scenarios were developed, hot spots were identified, and lab tests as well as field tests were carried out. A real cable stayed bridge in the Saarland region is available for monitoring within the frame of the project. Results from local investigations using guided waves and from monitoring field tests with micromagnetic sensors are presented and discussed. The results show the scenarios where the non-destructive methods are applicable and how the results can be used for structural health monitoring and maintenance concepts

Ultrasonic health monitoring in structural engineering: buildings and bridges

“…Electromagnetic acoustic transducer probes for cable monitoring torsional wave modes (left) and longitudinal wave modes (right) (from Kurz et al . ).…”

“…The problems with using PZT devices as embedded sensors and using EMATs with non‐metallic (concrete) structures remain. Bridge cables have been monitored with EMAT sensors for NDT‐based maintenance . Two types of EMATs were used to generate torsional and longitudinal waves, as shown in Figure .…”

Technological developments as an answer to bridge management challenges

“…The acoustic emission (AE) technique is based on the release of stored elastic energy as elastic waves due to sudden micro-fracturing in a rigid body. In the last decades several developments focused on the detection of wire rupture of suspension and stay cables and prestressing tendons [16][17][18].…”

“…It is potentially attractive for the inspection of anchorages embedded in massive concrete blocks. This technique is already used in industrial applications and is continuously improved by an active community in the world [17,[19][20][21].…”

The state of the art in structural health monitoring of cable-stayed bridges

“…However, the assumption on chord may not reflect the actual cable boundary conditions and nonlinearity of cables caused by sag. Kurz et al [42] analyzed the existing NDT methods and commented on suitable methods for different scenarios of cable elements. Methods for the accessible parts include magnetic inspection and AE monitoring.…”