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Finger joint fits like a glove
The finger expansion joints supplied for the Verrazzano Narrows Bridge in New York have to be tailored to precisely fit the existing steel structure following removal of the old expansion joints – a challenge made all the greater by their extraordinary size
The Verrazzano Narrows, a body of water which separates the New York boroughs of Brooklyn and Staten Island to the south of Manhattan, is the gateway to New York City’s harbor. The bridge that spans the Narrows creates a vital connection for road traffic, carrying about 200,000 vehicles per day. The double-decked suspension bridge has a central span of 4,260 feet (1,298 m), and was the longest suspension bridge in the world from the time its upper level opened in 1964 until 1981. Currently, it has the longest bridge span in the Americas.
All of the expansion joints in the bridge’s upper and lower deck have been replaced or substantially renewed, due to their age and deteriorated condition. The expansion joints are generally of the sliding finger type, and the largest of these accommodate deck movements of 2,700 mm (approx. 9 ft) – an extraordinary movement demand for a finger-type joint. Due to the great length of the individual fingers required to accommodate such movements, they are designed to receive intermediate support at their midspan. In fact, this type of sliding finger expansion joint is no longer used in modern bridge construction – except where required to replace an existing joint of the same type, as in this project.
The largest of the new joints, for movements of 2,700 mm (approx. 9 ft), are the largest-movement finger joints ever supplied by mageba – and the challenge of designing and supplying these exceptional devices has been only increased by the need to design them to precisely match existing geometry and conditions. The work involved also included the refurbishing of the retained elements and connecting steelwork, and conducting of off-site trial assemblies of the joints to ensure that they are properly dimensioned to suit the bridge – to ensure, as it were, that these carefully tailored finger joints fit like a glove.
