Croton Dam Spillway Bridge

The Croton Dam Spillway Bridge is a steel arch bridge over the spillway of the Croton Dam in Westchester County, New York.

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History

The construction of the New Croton Dam in the early 20th century included the building of an open-spandrel steel arch bridge over the dam spillway. ¹ The bridge was intended to provide access for dam construction and maintenance, but it later became a public road. ⁵ A $40,500 contract ⁵ for the bridge’s construction was awarded to the Baltimore Bridge Company on December 6, 1904, ³ and the bridge was completed by the end of 1905. ⁵ Initially, the design for the bridge was not specified, but a steel arch structure was ultimately chosen over a modified Pennsylvania through truss design. ²

Over time, the original bridge deteriorated due to exposure to roadway salt and spillway spray, leading to its replacement with a simplified arch design built of Corten steel in 1975. ^{2 5} Unlike the original bridge, which distributed load weight from the roadway to the abutments via the spandrels, loads in the new structure were concentrated at the center. The construction of the replacement bridge faced numerous difficulties, including poor working conditions caused by spray from the spillway and water accumulation in the box arch rib sections before welding. ⁵

An inspection of the replacement bridge conducted by Hardesty & Hanover revealed several issues, including inadequate seismic capacity, poor deck-bearing details, and insufficient anchorage at the arch bases. ⁵ The bearing plates showed upward displacements at the skewbacks, with arch base displacements up to 14 inches. There were also issues with the welds breaking and separating, and minor corrosion. Lastly, the seismic capacity of the bridge was inadequate due to a lack of anchorage at the arch bases and poor deck-bearing details.

It was initially thought that the structure could be rehabilitated. ⁵ To reach the original bridge load capacity, longitudinal stiffeners could be welded on the arch ribs and eliminate web bucking concerns, but they would be costly and difficult to install and introduce additional locations for the accumulation of moisture and debris. The siding bearings could also be replaced with multi-rotational bearings at deck level, and the arch bases could be secured, improving seismic performance. The welds could also be repaired.

But it was discovered that after the renovation contract was awarded and as crews were accessing the arch bases to field measure for the installation of the anchor bases, the bases were found to have displaced significantly further since the initial inspection. ⁵ An emergency inspection was conducted, which led to the bridge’s immediate closure. Consequently, an accelerated replacement project was initiated, with a design that mimicked the original 1905 bridge but utilized modern materials and design standards. ^{2 5} The design was completed by Hardesty & Hanover, with all permits and approvals obtained in a three-month compressed schedule. ⁵ The new plan included spandrel columns to distribute deck loads and prevent displacement of the arch bases, lateral seismic restraints at the deck level, and new anchorages at the skewbacks.

The bridge replacement contract was awarded to Kiewit Constructors, Inc., and work began in August 2003. ^{4 5} Initial fieldwork proceeded while shop drawings were prepared and steel fabrication by High Steel Structures, Inc. commenced. The new Croton Dam Spillway Bridge was completed in 2005 ² at a cost of $4.6 million. ^{4 5}

In that same year, the New York City Department of Environmental Protection put forward a proposal to implement a permanent road closure on the top of the dam in response to the terrorist attacks on September 11, 2001. The proposed closure would allow for pedestrian and emergency vehicle access while prohibiting motor vehicle traffic. Subsequently, a temporary barrier was installed and later replaced by permanent barriers upon the completion of a renovation project at the Croton Dam in 2011.

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Gallery

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Information

• State: New York
• Route: N/A
• Type: Steel Arch
• Status: Active - Automobile
• Total Length: 200 feet (1906); 200 feet (1975); 208 feet (2005)
• Deck Width: 20 feet (1906); 22 feet (1975); 23.6 feet (2005)
• Roadway Width: 19 feet (1906); 19 feet (1975); 20.4 feet (2005)
• Navigational Clearance:

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Sources

1. “New Croton Dam Spillway Bridge.” Hardesty & Hanover.
2. Fahn, Charlotte. “NEW SPILLWAY BRIDGE AT CROTON DAM TO EVOKE HISTORIC DESIGN.” Friends of the Old Croton Aqueduct, Spring 2004.
3. “New Highway Bridges at New Croton Reservoir.” Report to the Aqueduct Commissioners. 31 Dec. 1906, pp. 12, 55-56, 105.
4. “New Croton Dam Spillway Bridge.” National Steel Bridge Alliance.
5. Nyman, William E. “New Croton Dam Spillway Bridge.” Hardesty & Hanover, 2005.