20 Years of Experience with Structural Health Monitoring of Objects with CFRP Components

Abstract

The application of carbon fi ber reinforced polymers (CFRP) in bridge construction was before 1991 unknown. Therefore the bridge owners did not want to rely only on the laboratory experiments made in the 1980ties. They asked for structural health monitoring. This was also in the interest of the involved R&D community. The used devices range from "old fashioned" demec gauges for off-line measurements to classical foil resistance strain gauges, self-sensing systems for unidirectional CFRP wires, and also sophisticated integrated fi ber optical sensors with Bragg gratings. In the most important applications different independent systems were used in parallel. Twenty years are for devices which are exposed to outdoor weathering a fairly demanding time span. Therefore the surprisingly high reliability of most of these systems is a largely appreciated result. Applications on post-tensioned reinforced concrete bridges, stay cables, and pretensioned powerline pylons will be discussed.

The life times of polymer composites in construction

“…This project was as far most interesting as in this case the nominal post-tensioning stress in the cable cross sections is as high as 1610 MPa. More similar pilot projects have been presented in [5,6]. Parallel with the seasonal temperature fluctuation there is a fluctuation of the cable force ( Figure 6).…”

“…The CFRP cables with their anchorage heads have been equipped by the Empa with conventional sensors and also with state-of-the-art glass fiber optical sensors which provide permanent monitoring to detect any stress and deformation. Since 1996 the CFRP cables of the stork bridge are fully matching all the high expectations [6].…”

Prestressing concrete members with fibre‐reinforced polymer reinforcement: State of research

“…The major problem encountered by using FRP tendons for prestressing is how to provide a proper, reliable anchorage. 30,37 Susceptibility of composite tendons to transversal point loads and the possibility of interlaminar shear cause that the design of an anchorage system which can sustain the full static and fatigue strength is challenging. Furthermore, galvanic corrosion which occurs on the interface between carbon fibres and steel elements is problematic as well.…”

Reliability of long-term monitoring data

“…Therefore, it was of high interest to monitor the wire strains not only in the free part of the cable, but also within the anchor head. To transfer safely such high strains to the anchor head it was designed to linearly decrease the strain in the wires [1]. FBGs inside the head allowed this design to be verified (Fig.…”

“…Due to heavier vehicles and denser traffic, infrastructure is exposed to higher loads than they were designed for. New materials like CFRP and other composites have to be tested for their longterm behavior [1][2][3]. And for economic reasons the service life of bridges should be extended [4,5].…”