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When construction has been completed in 2023, the Corpus Christi Harbor Bridge, with its main span of 1661 ft (506 m) and full length of 5818 ft (1773 m), will be the longest cable-stayed segmental concrete bridge in the United States. Perhaps more noteworthy, though, is the extraordinarily long service life of 170 years that has been specified for the new structure. Faced with the challenge of getting the bridge on the right path to achieving this while minimizing long-term costs, its designers and constructors have recognized the critical importance of using the right key components in the bridge’s construction. The bridge bearings and expansion joints required by such long-span structures are typically highly engineered mechanical devices with sliding interfaces, and are thus far more prone to damage and deterioration than the bridge as a whole. Therefore, structural bearings and expansion joints can be expected to be replaced a number of times during the much longer lifetime of the more robust main structure. These key components can thus contribute much more to the total life-cycle costs of a bridge than their initial supply and installation cost at the time of the bridge’s construction would suggest. Consideration of the long-term costs associated with a bridge’s bearings, for example – including for supply, installation, maintenance and especially replacement – demonstrates the great importance of devoting adequate attention and expenditure to the procurement, installation and maintenance of high-quality components (as described in this article in Bd&e magazine). In the case of expansion joints the importance is even greater, considering the additional “user costs” associated with traffic disruption etc. Those costs typically arise during replacement works – with the initial costs of supply and installation of bridge expansion joints having been concluded by leading authorities to be “insignificant” in relation to the costs of joint replacement works when user costs are considered (as described in this paper from the 2012 IABSE congress in Seoul).
Recognizing the importance of minimizing long-term costs and traffic disruption, the Harbor Bridge’s design and construction team has been careful to use only high-quality, suitably selected and specified bearings and expansion joints in the bridge’s construction – components that can be expected to serve a very long service life with little or no need for maintenance or repair. We are pleased and proud that they selected mageba products to help achieve this objective, as supplying long-life low-maintenance products that will minimize impacts on the environment and on structure users is one of the main principles on which mageba is founded.
To support the bridge superstructure, mageba is supplying a large number of RESTON® DISC bearings. These include 12 enormous bearings for the main structure, each measuring up to 75 inches (1.9 m) across, designed for vertical service loads of up to 7,400,000 lb (equivalent to 33,000 kN) while also accommodating significant movements and/or resisting large horizontal loads. The 156 bearings being supplied for the approach structures are designed for lower loads of up to 3,350,000 lb (14,900 kN), but many of these are additionally required to temporarily resist movements during the construction phase and then to allow movements during the service phase, supporting the bridge’s construction method. The polyurethane (PU) rotational disc at the core of this bearing type is extraordinarily resistant to damage and deterioration, only experiencing plastic deformation at twenty times the design pressure.
To accommodate the superstructure’s movements and rotations while providing a driving surface for traffic, mageba is supplying bridge expansion joints of two types – modular and finger. The 8-gap TENSA® MODULAR joints (type LR) being manufactured for the ends of the main structure will accommodate movements of 24 inches (600 mm), while the TENSA® FINGER expansion joints (type RSFD) for the approaches have been designed for movements of up to 16 inches (400 mm). Both types have been designed and tested for exceptional durability. The more complex TENSA® MODULAR joint, for instance, has repeatedly been subjected to an unprecedented level of testing, including in accordance with the most demanding American standards (as described at the IBC Pittsburgh conference in 2013) – most notably in relation to fatigue performance.
Solutions that are heavily focused on sustainability – this is the way the engineering world is moving, and must continue to move, for the sake of our environment and our planet. At mageba, this has been our focus for many years already and will continue to be, for the long-term benefit of structure owners, structure users and society at large.
Bridge designer: FIGG
Contractor: Flatiron/Dragados JV
Owner: Texas Department of Transportation
Representation (proportional) of the life-cycle costs of a bridge’s expansion joints during the bridge’s full service life (typical) – with the initial supply and installation costs having been declared “insignificant” in the context of such life-cycle costs by NCHRP (Report 467) in the USA, and the TRRL in the UK