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As reported in our last Newsflash, mageba recently supplied the lock-up devices (LUDs, or STUs) required in the construction of this impressive and critically important structure. But that is not where our involvement in this project ended; mageba is currently also supplying the bridge’s expansion joints, a number of which have already been installed. The bridge was designed with expansion joints at 23 locations, dividing the two parallel decks into structurally independent sections. The use of modular expansion joints (with up to 18 movement gaps, to accommodate longitudinal movements of up to 54 inches (137 cm)) was anticipated, subject to prequalification and confirmation. The prequalification testing comprised of the performance tests defined in AASHTO Bridge Construction Specifications, Appendix A19, and seismic testing in accordance with the testing protocols of the California Department of Transportation (Caltrans). mageba’s TENSA®MODULAR joint was selected for use subject to successful completion of this very demanding testing. In fact, the seismic testing to Caltrans protocols of an 18-gap specimen of the TENSA®MODULAR joint was unprecedented for any type or make of modular expansion joint, as was the testing of daily opening/closing movements and traffic vibrations per AASHTO Opening Movement Vibration test specifications.
The bridge constructors also specified that all of the expansion joints, in spite of the enormous size of the 18-gap ones in particular, should be delivered from the factory in one piece. By avoiding the need for connecting together of sections on site (involving welding of transverse-running steel surface beams, insertion of rubber seals to span the gaps between the surface beams, and application of corrosion protection to the newly welded areas), a significant contribution can be made to enhancing an expansion joint’s life-cycle performance and resistance to fatigue. Carrying out all this work on a bridge construction site – exposed to inclement weather and construction schedule pressures and perhaps using processes and equipment that vary from their very standardized, highly controlled factory counterparts – can only introduce an element of risk to the quality and durability of the fully installed joint.
In the case of the largest 18-gap joints, each weighing in at 125,000 lbs (57,000 kg), transport to site as a single unit presented a particularly daunting challenge – quite likely an unprecedented one for a bridge expansion joint. First, each joint was transported from mageba USA’s factory in Pennsylvania to the bridge’s location on the Hudson River on a truck with a 12-axle trailer. The exceptional dimensions of each joint – 95 ft (29 m) long and 12 ft (3.5 m) wide – necessitated the provision of a police escort to ensure that the transport could be carried out safely with minimal impact on other traffic. Upon reaching the river, at one end of the uncomplete bridge deck, the expansion joint was lifted by crane onto a raft, floating on the water 160 ft (49 m) below. The raft was then pulled, together with a second, floating crane, into position beneath the edge of the bridge deck at the appropriate deck axis. With the raft adequately secured, the floating crane was used to lift the expansion joint up onto the deck. The joint was lifted right into position in the previously prepared recess in the concrete deck with great efficiency; within 45 minutes of being lifted off the raft, the positioning of the joint had been finalized – a notable achievement for a full-length expansion joint of such dimensions.
Thanks to the bridge constructor’s care in ensuring the quality and durability of the joints selected for use, and in avoiding the need for on-site welding together of sections, the owner of this fine new bridge, and the roughly 140,000 people that will use it every day, can thus have great confidence that the bridge’s expansion joints will perform very well for a very long time.