A pin and hanger assembly is used to connect two plate girders of a bridge. These assemblies are used to provide an

expansion joint A expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials. They are commonly found between sections of buildings, bridges, s ...

in the bridge. One beam (the ''anchor span'') is set on a pier with a short section

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

ed out toward the next pier. The other (the ''suspended span'') begins underneath the anchor span, and has its far end resting on the next pier. The beams have holes directly above each other. The two holes are connected using ''hangers'', a pair of connecting plates sandwiching the bridge girders. A pair of large steel pins through the plates and girder webbing provide the hinges, holding up the suspended span while allowing it to move longitudinally. Large washers are bolted to each end of the pin to retain the hangers. Exceptionally long spans may have two sets of girders cantilevered from opposite bridge piers with a third set of girders suspended by pin and hanger assemblies from both cantilevers.

Safety concerns

Pin and hanger assemblies are considered

fracture critical A fracture critical bridge is a bridge or similar span that is vulnerable to collapse of one or more spans as a result of the failure in tension of a single element. While a fracture critical design is not considered unsafe, it is subject to speci ...

bridge components, meaning that the assemblies are non-redundant and failure of these systems could cause part or all of the bridge to collapse. The collapse of the Mianus River Bridge in

Connecticut Connecticut ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the south. ...

exposed potential flaws with pin and hanger bridges that could lead to catastrophic failures, if left unchecked. Because of this, state departments of transportation incur costly expenses on bridges with pin and hanger assemblies, as they require constant inspection and maintenance. As a result of these safety concerns, and advances in bridge design to allow longer spans, pin and hanger assemblies are no longer used on new bridges in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Retrofitting

Attempts have been made to increase the safety of bridges with pin and hanger assemblies by adding some form of redundancy to the assembly. Retrofits that add redundancy to pin and hanger assemblies include adding a "catcher's mitt"a short steel beam attached to the bottom of the cantilevered girder that extends out beneath the suspended girder to "catch" the suspended girder should the pin and hanger assembly fail. Another redundancy is connecting the cantilevered and suspended girders at the pin and hanger assembly with welded blocks and

tie rod A tie rod or tie bar (also known as a hanger rod if vertical) is a slender structural unit used as a tie and (in most applications) capable of carrying tensile loads only. It is any rod or bar-shaped structural member designed to prevent the separ ...

s. Replacement options include bolted splices ( gusset plates) plus shear connectors; a link slab; a ship-lap joint; and a new pin and hanger assembly with improved materials.{{cite book , last1=Linzell , first1=Daniel , last2=Balakrishna , first2=Chandana , title=Steel Pin and Hanger Assembly Replacement Options , date=January 2017 , publisher=A Research Report Sponsored by Mid-America Transportation Center University of Nebraska-Lincoln Nebraska Department of Roads , location=University of Nebraska-Lincoln, USA , page=iii, 40-55 , edition=Report M042: Final Report: 26-1121-4031-001 , url=https://matc.unl.edu/assets/documents/matcfinal/Linzell_SteelPinandHangerAssemblyReplacementOptions.pdf , accessdate=17 August 2018

References

Structural connectors