Urs Meier

Carbon Fiber-Reinforced Polymers: Modern Materials in Bridge Engineering

This paper begins with a discussion of the large variety of modern materials recently employed or soon to find application in bridge construction. Since a comprehensive coverage of the subject exce...

CFRP BONDED SHEETS

Since 1984 in the static and fatigue loading tests at the EMPA laboratories, carbon-fiber reinforced plastic (CFRP) sheets have successfully been employed for the post-strengthening of flexural beams with a span up to 7 m. The results of this comprehensive research program show that the calculation of flexure in reinforced concrete elements post-strengthened with untensioned or with tensioned carbon-fiber reinforced epoxy-resin sheets can be performed analogous to conventional reinforced or prestressed concrete. In both cases long time fatigue tests on 7 m girders displayed an outstanding fatigue performance of this strengthening technique. A new approach also allows an increase of shear strength of the post-strengthened systems. In 1991, for the first time real structures were strengthened with CFRP in Switzerland e.g. the multispan box beam Ibach bridge near Lucerne with a total length of 228 meters and the City Hall of Gossau St. Gall. 1992 followed the historic wooden bridge near Sins which was strengthened for heavy trucks.

COMPOSITE MATERIALS IN BRIDGE REPAIR

This paper seeks to demonstrate how advanced polymer matrix composite materials developed for high-performance aircraft can offer major advantages for repairing ageing infrastructures. It focuses on the development and first applications of advanced rehabilitation, retrofitting, strengthening, and field monitoring technologies for civil engineering structures based on unique combinations of corrosion-resistant fibre-reinforced polymers and integrated fibre optic structural sensing.

Connecting high-performance carbon-fiber-reinforced polymer cables of suspension and cable-stayed bridges through the use of gradient materials

SummaryCarbon-fiber-reinforced polymer (CFRP) cables offer a very attractive combination of high specific strength and modulus (ratio of strength or modulus to density), outstanding fatigue performance, good corrosion resistance, and low axial thermal expansion. The high specific strength permits the design of structures with highly increased spans. The high specific modulus translates into a high relative equivalent modulus. This factor is very important in view of the deflection constraints imposed on large bridges. A relative high modulus coupled with a low mass density offer CFRP cables already an advantage for spans above 1000 m. Since 1980 EMPA has been developing CFRP cables for cable-stayed and suspension bridges that are produced as assemblies of parallel CFRP wires. The key problem facing the application of CFRP cables, and thus their widespread use in the future, is how to connect them. A new reliable anchoring scheme developed with computer-aided materials design and produced with advanced gradient materials based on ceramics and polymers is described. Early 1996 such CFRP cables with a load-carrying capacity of 12 MN (1200 metric tons) have been applied for the first time on a cable-stayed road bridge with a 124-m span. Each cable is built up from 241 CFRP wires having a diameter of 5 mm.

Fatigue crack propagation in 0°/90° E-glass/epoxy composites

The mode of fatigue crack growth is described for a 0/90° E-glass/ epoxy laminate under cyclic tension-tension loading. Crack growth appears to occur in a stepwise fashion with the crack remaining stationary for many cycles before each step of growth, whereupon a ligament of longitudinal ply at the crack tip is broken. A simple theory is described which assumes that the ligament at the crack tip is fatigued according to the S-N curve of the unnotched material. Using an assumed stress field and cumulative damage law, the number of cycles for initial growth from a notch and the rate of crack growth thereafter are predicted, and good agreement is demonstrated with experimental data.

Structural tensile elements made of advanced composite materials

This report outlines the merits of advanced fibrous composites for use in structural tensile elements, before presenting methods for structural reinforcement with cables and strips, giving examples of state-of-the-art applications, and analysing future trends.

Rehabilitation and retrofitting of existing structures through external bonding of thin carbon fibre sheets

This paper seeks to demonstrate how advanced polymer matrix composite materials developed for high-performance aircraft can offer major advantages for rehabilitation and retrofitting of existing civil engineering structures through external bonding of thin carbon fibre/epoxy (CFRP) sheets. Criteria for design of the use of this material are suggested. Retrofitting with CFRP sheets has been shown in cost comparisons with classical rehabilitation methods superior in most cases. (A) For the covering abstract see IRRD 869077.

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

The application of carbon fiber 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 fiber 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.

On the behaviour of hybrid aluminium/CFRP ☐ beams at low temperatures

Abstract In this paper results are presented of a theoretical and experimental investigation into a hybrid structural component in which a principal aluminium structure (Al) is reinforced with unidirectional carbon fibre-reinforced plastic (CFRP) laminates. The Al/CFRP ☐ beam was subjected to a temperature change of Δ T = −100°C, which is approximately the temperature change from initial room temperature (23°C) to the failure temperature of about −74.3°C. The dimensions of the beam in question were 30 mm × 30 mm × 210 mm. The thickness of the aluminium ☐ beam and the CFRP laminates was 2 mm and ≈1.1 mm, respectively. Due to the large difference in thermal expansion coefficients between aluminium (α A = 23.4 × 10 −6 °C −1 ) and high-modulus CFRP (in the fibre direction: α 1 C = −1.46 × 10 −6 °C −1 , E 11 C = 305GPa), stress concentration near the free edges causes delamination in the structure. The evidence indicates that the most important stresses, which are responsible for the mixed mode failure of the hybrid beam, are the interlaminar shear and interlaminar normal stresses. Furthermore, analytical two-dimensional models were developed to calculate these stresses, and these were compared with the results of a three-dimensional finite element model consisting of solid elements. Reasonable correlation was found between the results of the models presented. The strains were measured by strain gauges at different locations of the beam, and are compared with the theoretical analysis.

Box Girders under Extreme Long-Time Static and Fatigue Loading

This paper discusses aspects of the extreme long-time behavior of filament wound E-glass fiber reinforced epoxy box girders. Theoretical and experimental data are compared and show good agreement. The performance of these GFRP box girders during 25 years of static loading and 100 million fatigue cycles is excellent.