Mianus River Bridge

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Mianus River Bridge
Mianus River Bridge crop of HAER CONN,5-NEWHA,37-3.tif
The bridge in 1977. The 1983 collapse happened in the easternmost southern section (visible right)
Coordinates41°02′12″N 73°35′31″W / 41.03667°N 73.59194°W / 41.03667; -73.59194Coordinates: 41°02′12″N 73°35′31″W / 41.03667°N 73.59194°W / 41.03667; -73.59194
CarriesSix lanes of I-95 / Conn. Turnpike
CrossesMianus River
LocaleCos Cob, Greenwich, Connecticut
Official nameMichael L. Morano Bridge
Maintained byConnecticut Department of Transportation
DesignGirder and floorbeam
Clearance below70 feet (21 m)
Construction start1956[citation needed]

The Mianus River Bridge is a span that carries Interstate 95 over the Mianus River in the Cos Cob section of Greenwich, Connecticut. It is the second bridge on the site. The original bridge collapsed in 1983, killing three motorists. The replacement span is officially named the Michael L. Morano Bridge, after a state senator Michael L. Morano who represented Greenwich.


The bridge had a 100-foot (30.5 m) section of its deck of its northbound span collapse on June 28, 1983. Three people were killed and three more were seriously injured when two cars and two tractor-trailers fell with the bridge into the Mianus River 70 feet (21.3 m) below.[1][2]

Casualties from the collapse were few because the disaster occurred at 1:30 a.m., when traffic was low on the often-crowded highway.[3]


The collapse was caused by the failure of two pin and hanger assemblies that held the deck in place on the outer side of the bridge, according to an investigation by the National Transportation Safety Board.[4] Rust formed within the bearing of the pin, exerting a force on the hanger which was beyond design limits for the retaining clamps. It forced the hanger on the inside part of the expansion joint at the southeast corner off the end of the pin that was holding it, and the load was shifted to outside hanger. The extra load on the remaining hanger started a fatigue crack at a sharp corner on the pin. When it failed catastrophically, the deck was supported at just three corners. When two heavy trucks and a car entered the section, the remaining expansion joint failed, and the deck crashed into the river below.

The ensuing investigation cited corrosion from water buildup due to inadequate drainage as a cause. During road mending some 10 years before, the highway drains had been deliberately blocked and the crew failed to unblock them when the road work was completed.[5] Rainwater leaked down through the pin bearings, causing them to rust. The outer bearings were fracture-critical and non-redundant, a design flaw of this particular type of structure. The bearings were difficult to inspect close-up, although traces of rust could be seen near the affected bearings. An alternative hypothesis has been that so-called "sludge runners" (trucking companies who carry toxic waste) would regularly open their valves while crossing the bridge to dump some of their load and that the resulting chemicals ate away at the metal structure of the bridge.[6]

The incident was also blamed on inadequate inspection resources in the state of Connecticut. At the time of the disaster, the state had just 12 engineers, working in pairs, assigned to inspect 3,425 bridges. The collapse came despite the nationwide inspection procedures brought about by the collapse of the Silver Bridge in West Virginia in December 1967.


The interstate was not fully reopened for six months, and then only with a temporary truss. In total, final repairs cost over US$20 million. During the rebuilding, traffic was diverted onto US-1 and local streets in Greenwich, causing the worst traffic problems the town had ever seen. The Mianus River Bridge was completely reconstructed in the late 1980s. Work included replacing all of the structural steel, rebuilding and expanding the bridge deck to accommodate a wider roadway, and repairing the bridge piers to extend their service life. The replacement span was completed in 1992. It eliminated the pin-and-hanger assemblies that caused the collapse of the original bridge.[7]

Governor William O'Neill afterward proposed a US$5.5 billion transportation spending package to pay for rehabilitation and replacement of bridges and other transportation projects in Connecticut.

The replacement span is officially named the Michael L. Morano Bridge, after a state senator who represented Greenwich.

See also[edit]


  1. ^ "Mianus Bridge Disaster 1983". history.com. Retrieved August 31, 2012. CS1 maint: discouraged parameter (link)
  2. ^ Jeffrey, Schmalz (June 24, 1984). "Year after bridge collapse, questions and pain still linger". The New York Times. Retrieved July 26, 2015. CS1 maint: discouraged parameter (link)
  3. ^ Nguyen, Hoa (August 2, 2007). "Deadly Mianus disaster recalled". The Advocate. Stamford, Connecticut. pp. 1, A4.
  4. ^ Staff (July 19, 1984) "Collapse of a Suspended Span of Inter- state Route 95 Highway Bridge over the Mianus River" National Transportation Safety Board
  5. ^ "Mianus River Bridge Collapse". I-35W Bridge Collapse wiki. May 5, 2008.
  6. ^ Rosoff, Stephen, Pontell, Henry, and Robert Tillman: Profit Without Honor: White-collar Crime and the Looting of America. Pearson: 7th edition 2019, p. 130
  7. ^ http://faculty.up.edu/lulay/failure/MianusRiverBridgex.pdf

External links[edit]