North America (Change)

The Windsor-Detroit trade corridor is the busiest commercial land border crossing between Canada and the USA as well as an important trade and transportation route. Some 7,000 trucks cross the Windsor-Detroit border each day, totalling about 2.5 million trucks each year. In 2017, this represented over US$106.5 billion in bilateral trade. Currently, vehicular crossing is allowed via the Windsor-Detroit Tunnel and the Ambassador Bridge, neither of which provides direct highway connections.

The Gordie Howe International Bridge will provide an essential additional crossing option through six new lanes of traffic, ensuring effective and safe fl ow of people and goods between the two nations. The project involves a 2.5km long bridge, a port of entry in each country and the Michigan Interchange connecting to Interstate 75. Together, these four components will provide direct highway connections between the two countries, thereby reducing costs associated with shipping and reducing greenhouse gas emissions and other pollutants resulting from idling vehicles. Key features, such as a multi-use path for pedestrians and cyclists, LEED Silver rating for buildings and a community benefits plan, will result in positive environmental and community impacts as well. The bridge is named the Gordie Howe in recognition of the legendary hockey player, a Canadian who led the Detroit Red Wings to four Stanley Cups.

The idea for the new crossing has been under study since 2000, but it was in July 2018 that the owner, Windsor-Detroit Bridge Authority (WDBA) announced that Bridging North America (BNA) had been selected as the preferred proponent to design, build, finance, operate and maintain the Gordie Howe International Bridge project through a public-private partnership. BNA is a partnership of Fluor, ACS Infrastructure Canada and Aecon Group. Aecom is BNA’s design engineer/engineer of record.

After signing a US$5.7-billion fi xed-price contract, BNA started construction in 2018, presenting a 74-month construction schedule to complete the four components of the project with the bridge expected to be in service by the end of 2024. WDBA is a not-for-profit Crown corporation of Canada responsible for the delivery and operation of the Gordie Howe International Bridge. Parsons, as owner’s engineer (OE), has worked with WDBA to determine project requirements and to evaluate proponents, and is now overseeing design and construction.

All proponents were required to present design options for the main bridge spanning the Detroit River that were either cable-stayed or suspension. The design submitted by BNA is a 2.5km long bridge, comprising a 1,562m long cable-stayed bridge plus approaches. The towers are 219m tall and are built on the ground because of commitments made through the environmental study process to limit impacts to commercial users of the Detroit River and to limit impact on the natural environment. This resulted in the 853m-long clear span, breaking the record for the longest main span of any cable-stayed bridge in North America. This is only 3m shorter than the main span of Normandy Bridge, from which the Gordie Howe International Bridge design concept is inspired.

The depth of the bedrock is approximately 30m at the site of the cable-stayed bridge, the top layer consists of limestone, followed by dolomitic and dolostone rock types. Artesian conditions at the interface of overburden and bedrock were confirmed by geotechnical investigations, as well as the presence of hydrogen sulphide in the groundwater.

Another environmental challenge of the site is it is prone to maximum one-hour mean speed up to 42m/s and three-second gusts of up to 60m/s at deck level. The site is in a stable continental region, recording low levels of seismicity in historical times, with only 22 events having been reported within 100km of the site. Potential ship impact forces are high, making it one of the governing load cases for tower design.

WDBA and the OE defined the design requirements for the bridge. One driving requirement is a dual-track design approach where the most stringent of a series of US design standards and of Canadian design standards are applied to the whole length of the bridge. Namely, the CHBDC S6-14 edition for the Canadian track, and AASHTO LRFD 8th edition for the US track. A project-specific, live-load study was conducted while developing the design requirements to defi ne live load configurations and combinations used in design, comprising commercial vehicle lanes and mixed vehicle lanes to represent the unique traffic pattern for border crossing. Another key element of design requirements for the bridge, driving most construction specifications developed by the designer, is a 125-year required service life for all permanent elements which shall be demonstrated by the designer with a detailed durability plan, involving the use of Stadium for service life modelling. Other unique features include a requirement for all steel tension members and connections to be designed with redundancy provisions for the future installation of an active stay-deicing system involving real time meteorological monitoring, and wind tunnel testing.

The cable-stayed bridge deck is 37.5m wide and consists of steel edge girders, steel floor beams, and longitudinal redundancy girders, all composite with a concrete deck slab. Precast concrete deck panels are transversely post-tensioned along the entire length and longitudinally post-tensioned near the ends of the bridge as well as in the centre of the main span. The deck system is enclosed into a box shape by the bottom soffit system and two aerodynamic claddings on the side. A total of 216 stays, organised in two planes, connect the outside edges of the deck to the two reinforced concrete A-shaped towers. The top of each tower rises up to 219m above the footings, and the tower head as well as its legs are hollow sections, except a portion of the legs around deck level.

The stay cables are parallel-strand system with individually sheathed and filled 7-wire 150mm2 strands, varying in number from 38 to 122, encased in an outer extruded HDPE sheath. Tower stay anchors are steel boxes inside the box-shaped concrete tower head, and deck anchors are pipe-shaped anchors attaching to the exterior sides of the steel edge girders. At grade level, a 49m long post-tensioned tie-beam connects the two tower leg footings, balancing the horizontal reaction forces coming from the inclined tower legs. Tower foundations are composed of 12 drilled shafts per tower (six per footing), 3m in diameter.

Each backspan is supported by two concrete side span piers and one concrete anchor pier. Two hollow reinforced concrete columns form each of the backspan piers, where each column is founded on one single 3m diameter drilled shaft. Only at the US tower the deck is permanently fixed longitudinally through restraint between tower leg corbels and steel longitudinal bearing brackets attached to the steel deck system. At the Canadian tower, lock-up devices will allow slowly induced longitudinal movements such as temperature variations, but will lock and provide fixity under wind, seismic or other dynamic load movements. As a result, the modular joint on the Canadian end of the cable stayed bridge needs to accommodate about twice what is required of the US modular joint.

The bridge will be equipped with an inspection gantry which can ride along the bottom soffit from one end to the other. Access ladders and platforms will allow inspection inside and outside the piers, while elevators will allow access inside the hollow portions of the towers. Aesthetic lighting on the bridge will be developed in conjunction with an artist and considered to be a public art commission.

The project required the bridge to be protected from unacceptable damage due to aberrant vessels operating in the river, taking account of the seawalls and auxiliary structures. Equivalent forces used in analysis for design purpose are a full vessel collision force of 160MN applied on the seawalls at ±30° from the centreline axis of the navigation channel, half the vessel collision force (80MN) applied perpendicular to the seawalls and a ship collision force on the superstructure with mast of 2.2MN.

The other governing load for tower foundation design is wind. Wind loads on the cable-stayed bridge were established by wind tunnel testing conducted by RWDI and were used to determine construction phases. Work at the site is progressing with deep foundations for the cable-stayed bridge nearing completion. At the start of drilled shafts construction work, crews on each side of the river performed a full-size test/technique shaft to verify, not only geotechnical and structural capacity, but also means and methods.

Tower footing construction work is under preparation, with concrete sample panels being cast and inspected to ensure uniformity of the tower aesthetics, and with construction mockups being prepared for footings and tower legs that will allow verification of key construction means and methods, as well as of materials and techniques used for patching and small repairs. Construction of the two towers is scheduled for completion in 2022, while construction of the backspan superstructure is expected to finish in 2024. BNA has elected to build the backspan superstructure using a series of temporary bents. This will allow start of construction of the deck prior to the towers being completed. Overall completion of the bridge and opening is planned for the end of 2024.

Zaher Yousif is senior director, bridges and roads, Windsor-Detroit Bridge Authority; Matthew J Chynoweth is chief bridge engineer and director of Bureau of Bridges and Structures, Michigan Department of Transportation; Martin Furrer is programme director at Parsons