PSI - Issue 64

Tom Argyle et al. / Procedia Structural Integrity 64 (2024) 1376–1385 Argyle et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 9. (a) temperatures during application of binder course. (b) temperatures during application of wearing course

The trials validated the theoretical models that had been developed and confirmed that the resin remained below its glass transition temperature, and therefore retained its design strength, for the proposed construction sequence. 6. Detailed design Strengthening was undertaken on Swanley I/C East first. This structure three spans of lengths 10.40 m, 26.67 m, 14.68 m. The deck is 12.4 m wide and curved on plan. There is a skew of 9° and a horizontal radius of 259.1 m through the centreline of the structure. The superstructures consist of reinforced concrete solid slab type deck in the back spans and over supports, with a reinforced concrete beam and slab type deck in the central span. The decks are continuous over the intermediate supports, which consist of integral inclined reinforced concrete piers supported on thrust blocks and spread footings. To determine the CFRP rod requirements, a structural analysis was carried out using the software Midas Civil (2020). The bridge was modelled using as a linear elastic grillage, with longitudinal grillage elements placed at the centre lines of the beams, and the spacing of the transverse elements were defined to coincide with the midspan diaphragms. Skew and curvature were also considered in the model. The boundary conditions were assumed fully fixed at the foundations and pinned at both ends of the span. Loadings were applied in accordance with the National Highways assessment standards CS-454 (2020) and CS 458 (2020), to ensure the revised design was compatible with the wider assessment rating of the structure for the Normal Traffic and the necessary Abnormal Vehicles. The CFRP strengthening was designed to the requirements of the National Highways standard CD 371 (2022), and in the absence of a Eurocode design standard covering the strengthening of structures with CFRP, the Concrete Society guidance TR 55 (2013) was used. During the works, it was necessary to retain one of the two lanes open to public traffic, to minimise disruption of the works. As such, the deck would be subject to Normal Traffic across approximately 50% of is width and so a sequenced replacement was required to always maintain sufficient capacity in the structure. The design, therefore, required a minimum number of competent existing steel strengthening plates to be left in place whilst new CFRP rods were installed elsewhere. Once these installed CFRP rods were effective, the remaining steel plates could be removed and replaced. Therefore, a section capacity check was carried out and concluded that one steel plate must be retained in each zone, see Fig. 10. Each zone corresponds to a longitudinal beam in the grillage. A reduction in tensile bond strength of 10% was therefore considered in the design to allow curing of the CFRP epoxy resin in the presence of vehicles vibrations and deck strains as recommended in TR 55.