Highway Accident Report

Adopted-. July 19,1984
COLLAPSE OF A SUSPENDED SPAN
OF ROUTE 95 HIGHWAY BRIDGE
OVER THE MIANUS RIVER
GREENWICH, CONNECTICUT
JUNE 28, 1983

NTSB Number: HAR-84/03
NTIS Number: PB84-916203


SYNOPSIS

At 1:30 a.m., e.d.t., on June 28, 1983, a 100-foot-long suspended span between piers 20 and 21 of the eastbound traffic lanes of the Interstate Route 95 highway bridge over the Mianus River in Greenwich, Connecticut, collapsed and fell 70 feet into the river below. Two tractor-semitrailers and two automobiles plunged Into the void In the bridge and were destroyed by impact from the fall, Three vehicle occupants died, and three received serious injuries.

The suspended span which collapsed was attached to the bridge structure at, each of its four corners. To support the weight of the northeast and southeast corners of the suspended span, each corner was attached to the girders of the cantilever arm of an adjacent anchor span by a pin and hanger assembly. The pin and hanger assembly includes an upper pin attached through the 2 1/2-inch-thick web of the girder of the cantilever arm and a lower pin attached through the 2 1/2-inch-thick web of the girder of the suspended span. One and one half-inch-thick steel hangers connect the upper and lower pins-one on the inside and one on the outside of the web.
Sometime before the collapse of the suspended span, the Inside hanger in the southeast corner of the span came off of the inside end of the lower pin. This action shifted the entire weight of the southeast comer of the span onto the outside hanger. The outside hanger gradually worked Its way farther outward on the pin, and over a period of time, a fatigue crack developed in the top outside end of the upper pin. The shoulder of the pin fractured off, the pin and hanger assembly failed, and the span collapsed into the river.

The National Transportation Safety Board determines that the probable cause of the collapse of the Mianus River bridge span was the undetected lateral displacement of the hangers of the pin and hanger suspension assembly in the southeast corner of the span by corrosion-induced forces due to deficiencies in the State of Connecticut's bridge safety inspection and bridge maintenance program.

RECOMMENDATIONS

As a result of its investigation of this accident, the National Transportation Safety Board made the following recommendations:

-to the Connecticut Department of Transportation:

Reopen the paved-over drains on the Mianus River bridge and any other bridge in Connecticut which may have paved-over drains, institute a program to modify the bridge drainage systems so that they provide for proper runoff of surface water and to require require regular cleaning and maintenance of drainage systems. (Class II, Priority Action) (H-84-31)

Establish and enforce a policy of reviewing and evaluating proposed modifications of bridge drainage systems to preclude reducing the effectiveness of the systems. (Class II, Priority Action) (H-84-32)

Require the cleaning of critical elements of bridges and access routes thereto immediately before or in the course of major bridge safety inspections. (Class II, Priority Action) (H-84-33)

Improve the quality of review of bridge inspection reports, and provide for face-to-face reviews of reports on a selected sample of bridges by reviewers and inspectors. (Class II, Priority Action) (H-84-34)

Revise Bridge Inspection Form BRI-18 (Ed. 1-81) to provide for the recording of information regarding:

(1) specified critical elements with individual ratings supported by a narrative explanation;

(2) observations and measurements of alignment of members; and

(3) use of specialized equipment to gain access to the bridge area being inspected or the reasons why specialized equipment was not used. (Class II, Priority Action) (H-84-35)

Prepare individual Inspection and maintenance manuals for large or complex bridges within Connecticut. (Class III, Longer Term Action) (H-84-36)

After consultation with the Bridge Safety and Inspection Section, install as necessary, handholds, safety belt connections, handrails, catwalks, and safety wires on existing bridges to assist inspectors in safely moving through the superstructures and gaining access to critical elements of the bridge. (Class III, Longer Term Action) (H-84-37)

Review the bridge safety inspection manuals and bridge maintenance manuals and voluntary standards of the American Association of State Highway and Transportation Officials and Incorporate those which affect bridge safety into the Connecticut Department of Transportation bridge safety inspection procedures and bridge maintenance practices. (Class II, Priority Action) (H-84-38)

Require that a representative of the Bridge Safety and Inspection Section review the plans for new bridges for safe and effective inspectability and maintainability before acceptance of the design. (Class 14 Priority Action) (H-84-39)

-to the Federal Highway Administration:

Develop a detailed and comprehensive integrated bridge inspection procedure using all available source materials, including but not limited to the Federal Highway Administration's "Bridge Inspector's Training Manual" and the American Association of State Highway and Transportation Officials' "Manual for Bridge Maintenance (1976)" and "Manual for Maintenance Inspection of Bridges (1978)." (Class II, Priority Action) (H-84-40)

Amend 23 CFR 650.303 to include an -integrated bridge inspection procedure in its entirety or to Incorporate such a procedure by reference. (Class III, Longer Term Action) (H-84-41)

Develop a model bridge inspectors field handbook in a convenient checklist format which encompasses all the elements of an integrated bridge Inspection procedure to be prescribed by 23 CFR 650.303 if amended as recommended by the Safety Board. (Class II, Priority Action) (H-84-42)

Establish a bridge inspection enforcement program that will assure compliance with 23 CFR 650.303 If amended as recommended by the Safety Board. (Class II, Priority Action) (H-84-43)

Develop and disseminate procedures for Inspection of hidden elements of pin and hanger assemblies which do not involve the dismantling of the assemblies. (Class III, Longer Term Action) (H-84-44)

Prescribe objective dimensional standards for the alignment of bridge spans to facilitate detection of misalignment caused by deterioration of pin and hanger assemblies. (Class II, Priority Action) (H-84-45)

In cooperation with the States, identify bridges that have a pin and hanger assembly design using bearing stresses above those allowed by the 1983 Interim Specification--Bridges, 1983 of the American Association of State Highway and Transportation Officials, and designate them for frequent Inspection. (Class II, Priority Action) (H-84-46)

Augment the current inventory and rating methodology of the National Bridge Inspection Standards, which emphasizes an overall rating for planning large-scale replacement or rehabilitation funding, to require inspections and ratings of sufficient depth and detail to address all elements critical to safety. (ClassII, Priority Action) (H-84-47)

Require that the design of any Federal-aid bridge include an analysis of inspectability and maintainability. (Class II, Priority Action) (H-84-48)

Conduct detailed inspections of the Mianus River bridge and other representative bridges having a skewed and nonskewed suspended span design with pin and hanger assemblies to determine whether there is a significant difference between the two designs in terms of the movement of hangers on pins due to either dead or live loading and whether such movement is acceptable. (Class III, Longer Term Action) (H-84-49)

Require each State to develop an individualized Inspection procedure for each bridge under State Inspection jurisdiction that has critical elements whose failure will almost certainly result in a catastrophic failure of the bridge. (Class II, Priority Action)(H-84-50)

Prescribe criteria for in-depth inspections of pin and hanger assemblies based on objective measures of the risk of hidden deterioration, such as the time since the last inspection, and/or whether the pin and hanger assembly is dismantled. (Class II, Priority Action) (H-84-51)

Prescribe an objective standard for repair or replacement of pin and hanger assemblies according to measured conditions of misalignment, distortion, or changes In the position of elements of the assembly. (Class II, Priority Action) (H-84-52)

Change the format of the "Bridge impector's Training Manual" to provide for page-change updating, to key the manual to inspection forms, to prescribe mandatory examinations and inspector evaluations of Individual critical elements as well as overall conditions, and to describe an optional methodology for effective on-site inspection. (Class II, Priority Action) (H-84-53)

Include in the annual bridge Inspection program audit a review of the State's bridge inspection training programs. (Class II, Priority Action)(H-84-54)

-to the American Association of State Highway and Transportation Officials:

Modify Article 1.7.27 of the "Standard Specifications for Highway Bridges (1977)" and succeeding "Interim Specifications" to describe forces which might result in lateral movements of members on pins to be considered in designing pinned assemblies. (Class II, Priority Action)(H-84-55)

-to the U.S. Department of Transportation:

Direct the DOT Inspector General to review the Federal Highway Administration's bridge inspection audit program for its sufficiency in establishing State compliance with the National Bridge Inspection Standards. (Class II, Priority Action) (H-84-56)

-to the American Institute of Steel Construction:

Review the pin cap detail shown in the AISC Manual of Steel Construction to determine if it should be deleted from the manual or if qualifying conditions should be attached to its use. (Class II, Priority Action) (H-84-57)

-to the National Committee on Uniform Traffic Laws and Ordinances:

Modify Section 12-220 of the Uniform Vehicle Code to require the use of hazard warning signals whenever a motor vehicle becomes a hazard to motorists on a highway. (Class III, Longer Term Action) (H-84-58)