The frequency and cost of bridge repairs in Europe have increased significantly. This is due to higher traffic loads than those expected during initial design, harsh environmental conditions, use of de-icing salts, poor construction material quality and limited maintenance.
Novel ways of designing and retrofitting steel-concrete composite bridges
External post-tensioning is a recognised robust retrofitting method for the rehabilitation of existing bridges and construction of new ones. “To exploit the advantages of non-corrosive property and high strength, fibre-reinforced polymer (FRP) composites are being increasingly used for external tendons instead of conventional steel ones,” explains Theodore Karavasilis, coordinator of the EU-Funded TimePresCompBridge project. Tendons are steel cables or wires used in prestressed concrete structural elements like beams. Existing research on externally prestressed steel-concrete composite bridges has focused on short-term loading. This research was undertaken with the support of the Marie Skłodowska-Curie programme. “However, the inevitable loss of long-term performance of prestressed composite bridges is of primary concern in practice, especially when FRP tendons are used,” observes Karavasilis. Prestressed concrete is a type of concrete used in construction that is considerably compressed during production to strengthen it.
Assessing effectiveness of external FRP tendons
Project partners developed a robust analysis and design technique for steel-concrete composite bridges that are prestressed with external FRP tendons. They evaluated flexural performance and quantified secondary moments in two-span prestressed steel-concrete composite beams. A parametric numerical investigation examined the effectiveness of strengthening a continuous steel-concrete composite beam with external tendons of different cross-section areas. In addition, TimePresCompBridge investigated secondary moments in continuous prestressed composite beams that have different tendon layouts under symmetrical and unsymmetrical loads. Results indicate that external prestressing not only significantly increases the ultimate load-carrying capacity, but also improves the moment redistribution ability of continuous steel-concrete composite beams. Moreover, the analysis shows that important secondary moments are present in continuous prestressed composite beams throughout the loading history. “Therefore, it’s necessary to consider secondary moments in the strength design of these types of bridges,” notes Karavasilis. The researchers evaluated the use of external FRP tendons instead of steel ones for prestressing steel-concrete composite girders. They performed numerical simulations on single- and two-span prestressed composite girders. In particular, carbon fibre-reinforced polymer (CFRP), aramid fibre-reinforced polymer (AFRP) and conventional prestressing steel tendons were compared for prestress levels ranging from 0 % to 60 %. “Results demonstrate that the behaviour of girders with CFRP and steel tendons is similar, while AFRP tendons result in lower ultimate load and higher deformation capacity,” adds Karavasilis. “TimePresCompBridge has responded to the need to design new bridges that are more economical, use less material and have longer lifespan, and to upgrade and maintain our bridges with minimal traffic and business interruption,” concludes Karavasilis. As a follow-up to the project, the consortium is currently evaluating the competitiveness of prestressed steel-concrete composite bridges with external FRP tendons in real life by considering both structural performance and cost.
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