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Time-dependent design and assessment of prestressed steel-concrete composite bridges with external FRP tendons

Periodic Reporting for period 1 - TimePresCompBridge (Time-dependent design and assessment of prestressed steel-concrete composite bridges with external FRP tendons)

Reporting period: 2017-10-01 to 2019-09-30

Large EU projects and surveys reveal that the frequency and cost of bridge repairs in Europe have significantly increased due to traffic loads higher than those considered in the initial design, harsh environmental conditions, use of de-icing salts especially in countries with cold climates, poor quality of construction materials, and limited maintenance. Most importantly, the aforementioned projects and surveys highlight that current repair and strengthening methods are costly and time-consuming and result in large socio-economic losses due to disruption of traffic flow such as travel delays, longer travel distances, insufficient move of goods, and loss of business. Therefore, bridge owners and bridge engineers urgently seek to transfer into real-life projects more efficient and less disruptive methods for bridge repair, strengthening and maintenance. External post-tensioning is recognised as a powerful technique in the rehabilitation of existing bridges as well as in the construction of new bridges. For the advantages of noncorrosive property and high strength, fibre reinforced polymer (FRP) composites are being increasingly used for external tendons instead of conventional steel ones. Existing research on externally prestressed steel-concrete composite bridges has focused on the short-term loading. However, the inevitable loss of long-term performance of prestressed composite bridges is of primary concern in practice, especially when FRP tendons are used. Therefore, it is necessary to investigate deeply the long-term behaviour of these bridges and, on this basis, to propose practical design guidelines. In this fellowship, an experimental and numerical study has been carried out to understand the time-dependent performance of composite girder bridges with FRP tendons. Long-term tests were performed. Moreover, a novel computer programme capable of performing time-dependent analysis was developed and used to conduct an extensive numerical investigation.
An experimental and numerical study was carried out to investigate the long-term behaviour of prestressed steel-concrete composite girders with external FRP tendons. A novel finite element model for predicting the short-term and long-term behaviour of prestressed steel-concrete composite girders with external steel and FRP tendons were developed. The time-dependent effects considered in the proposed model included concrete creep, concrete shrinkage and tendon relaxation. Comprehensive aspects of behaviour of prestressed composite girders subjected to short-term and long-term sustained loads were investigated. Long-term tests were performed, and extensive parametric numerical investigation was carried out by using the proposed model. The results show that the long-term prestress loss of girders with FRP tendons was considerably higher than that of girders with steel tendons and that increasing the quantity of reinforcing steel led to a decrease in long-term downward deflection. The long-term behavior of prestressed composite beams was dominated by concrete shrinkage. In addition, the influence of prestress level on the moment at the center support of continuous prestressed composite girders was marginal due to the presence of secondary moments. The study also shows that the influence of secondary moments on moment redistribution was less pronounced in prestressed composite girders with AFRP tendons than in prestressed composite girders with CFRP or steel tendons. Based on the experimental and numerical study, practical design equations were developed to calculate the time-dependent deflection at service sustained loads and moment redistribution in prestressed composite girders. The results of the research work have led to 5 articles published in leading international journals, while some of the results were presented in international conferences (ICCE-26 and MECHCOMP 2019).
The progress against the background of the state-of-the-art is the development of a robust analysis and design method for steel-concrete composite bridges that are prestressed with external steel and FRP tendons and are subjected to long-term sustained loads. Specific progress is summarised as follow: development and validation of a specialized software for time-dependent analysis of composite girders with external steel and FRP tendons; evaluation of the long-term performance of externally prestressed composite girders through laboratory tests and parametric analyses using the specialized software; development of a practical time-dependent design method for prestressed composite girders with external steel and FRP tendons in the context of Eurocode 4; and evaluation of the competitiveness of externally prestressed composite bridges in practice by considering both performance and cost. The expected results of the project timely respond to the sustainability and socio-economic needs of modern societies. The European society will significantly benefit from the fellowship and the project will increase the competitiveness and attractiveness of the European Research Area.