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Trunk H ighway 61 (TH 61) runsalong the scenic north shore of LakeSuperior in Minnesota. The highwaycrosses the Gooseberry River withinGooseberry Falls State Park, whichattracts 580,000 visitors annually. Builtin 1922, the old bridge over the river

consisted of a 150 arch shaped decktruss with 60 beam spans at both ends.A third arch was added, in 1937, toaccommodate a 30 roadway with 5 side-walks on both sides, which act as viewingplatforms for waterfalls located west andeast of the bridge. A visitor center islocated near the north end of the bridgeand there is also an additional roadsideparking at the south end, both of whichmake the area around the bridge heavilycongested with pedestrian traffic andcause safety concerns.

By 1990, the bridge was badly deteri-

orating. An arch type bridge was chosenfor replacement in order to maintain thelook of the old bridge from both theupper and lower falls, where it frames theriver gorge scenery. The new bridgewould be built in conjunction with a newvisitor center located away from the road.

The new bridge consists of a 154main steel arch span supporting a 14deck slab with three concrete slab spanson both ends varying in length from 16to 24. The cross-section for the mainspan consists of 2 box shaped fixed arch-es 42.5 deep by 29.5 wide. In order tomaintain bridge access for pedestrianviewing of the waterfalls, and at the sametime reduce pedestrian traffic on thehighway, an 8 walkway was provided atdeck level on one side of the bridge withanother 8 walkway suspended below thebridge on the other side. These walkwaysconnect with trails that run throughoutthe park. Tubular steel sections wereused for the pier columns, spandrelcolumns, the struts that brace the archesand the tension members which suspendthe walkway underneath. A slab span sys-tem which runs between the pier andspandrel cap beams was chosen to reduce

superstructure depth and to be more aes-

Modern Steel Construction / July 2000

T runk H ighway 61 over

Gooseberry RiverLake County, Minnesota

Merit Award: Medium Span

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thetically pleasing. The new pedestrianrailing was designed to look similar to theold rail for historic reasons. During theGreat Depression, rock walls located atthe south abutment of the old bridge hadbeen built by the Civilian ConservationCorps. These walls were saved and thenew abutment, directly adjacent to the

old, was constructed with a rock facing tomatch the old wall.

TH 61 is the only road along thenorth shore to Canada and no practicaldetours are available. This coupled witha tightly confined area made stage con-struction a requirement. Due to the steepslopes and an environmentally sensitivearea the contractor was constantly chal-lenged during construction.

Modern Steel Construction / July 2000

Project Team

OwnerMinnesota Department ofTransportation

DesignerMinnesota Department ofTransportation

Steel FabricatorThe D.S. Brown Company-Lewis Engineering Division

Steel DetailersThe D.S. Brown Company-Lewis Engineering Divisionand Tensor Engineering Co.

Steel Erector

M.A. Mortenson Company

General ContractorsM.A. Mortenson Company