Mianus River Bridge
|Mianus River Bridge|
|Official name||Michael L. Morano Bridge|
|Carries||Six lanes of I-95 / Conn. Tpk.|
|Locale||Cos Cob neighborhood of Greenwich, Connecticut|
|Maintained by||Connecticut Department of Transportation|
|Design||Girder and floorbeam|
|Clearance below||170 metres (560 ft)|
The Mianus River Bridge carries Interstate 95 over the Mianus River in the Cos Cob section of Greenwich, Connecticut. The bridge suffered a 1983 collapse, killing several motorists. The replacement span is officially named the Michael L. Morano Bridge, after a state senator who represented Greenwich.
The bridge had a 100-foot (30.5 m) section of its deck of its southbound span collapse on June 28, 1983. Three people were killed when two cars and two tractor-trailers  fell with the bridge into the Mianus River 70 feet (21.3 m) below; three were seriously injured.
Casualties from the collapse were few because the disaster occurred at 1:30 a.m., when traffic was low on the often crowded highway.
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. The hanger on the inside part of the expansion joint at the southeast corner was forced from the pin that was holding it, and the load was shifted to the only other pin in the joint. The problem was caused by rust formation within the bearing on the pin, exerting a force on the hanger which was beyond design limits. The extra load on the remaining pin 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. 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.
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 that accommodated two northbound lanes of traffic instead of the usual three. 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.
See also 
- "Mianus Bridge Disaster 1983". history.com. Retrieved 31 August 2012.
- "Part Of Bridge On Route I-95 Falls Into River In Greenwich,; Killing 3.". New York Times. June 29, 1983. "A 100-foot section of a Connecticut Turnpike bridge collapsed here early this morning, hurling four vehicles into the Mianus River, killing three people and critically injuring three others. 'I thought I heard an explosion,' said Gordon Gilman, whose home is on the river bank. 'I looked out the window and I saw a truck and a car coming off the bridge and going into the water. Then I could hear moans. I could hear people moaning.' Connecticut officials said they could not explain the collapse, and Gov. William A. O'Neill and the National Transportation Safety Board ordered investigations."
- Hoa Nguyen, "Deadly Mianus disaster recalled"], The Advocate, Stamford, Connecticut, August 2, 2007, pp 1, A4