Contributed Case History: Building Bridges with Steel Girder Formwork
A girder bridge is considered the most common and most basic bridge type. In its simplest form, a log across a creek could even be considered a girder bridge. In today’s bridges the long spans allow for a direct connection between two areas without disturbing the area and the wildlife below. The long concrete spans can reach from one side of a river to the other side allowing for minimal disruption below and resulting in a beautiful, functional bridge. Building these concrete bridges requires specialized forms that can accommodate any challenges brought on by the long spans and provide a quick, safe, working solution.
On the Indian Street Bridge and Donald Bridge projects, a girder form system proved to be the optimal solution for building these complex bridge designs. With its self-spanning feature, the girder from system allowed for speedy assembly and disassembly, and quick cycle and reconfiguration times when forming the various shaped pier columns and caps.
Indian Street Bridge
The 3,100-ft. long Indian Street Bridge was designed to provide additional access between the cities of Palm City and Stuart to ease traffic congestion. The new bridge will cross the South Fork of the St. Lucie River in Martin County, as a direct connection between the two cities.
The bridge design has intricate piers with 18 multi-span hammerhead caps. The columns have a wide reveal on the face and large chamfers that continue into the cap. The multi-span hammerhead caps have the reveals die into them with the chamfer transitioning into the cap and feathering.
The 120-ft. long caps and designs called for innovative techniques to be used onsite. To support the formwork off the jacks, Doka used a rocker to distribute the loads instead of a typical spreader beam. Another challenge was to design a form for the custom chamfers and reveals that met the requirements of the project and were also efficient to strip. The reveals and chamfers not only were feathered in design but also had a radius face adjoining intersecting angles.
The Steel Girder forms proved to be the optimal choice because they can span large distances without any additional support or shoring. Additionally, the forms are modular and can be ganged and picked in large sections.
Currently the contractor is involved in setting reinforcing steel and placing concrete for bridge footings, columns and caps, as well as continuing the superstructure construction and setting the beams.
Doka worked closely with Archer Western Contractors to ensure that the formwork solutions chosen would work with the intricate details of the design and to adapt to all changing conditions.
Bridge construction began in April 2011 and completion is expected in April 2013.
To improve safety, mobility and capacity for the traveling public, a replacement bridge and approaches were commissioned in Golden, British Columbia, to widen the current stretch of the Trans-Canada Highway from two lanes to four.
The contractor, Flatiron Constructors Canada Ltd., was tasked with forming two four lane bridges. The first was a new four-lane 300-meter long bridge over the Columbia River and the second was a new four lane 130-meter long bridge crossing the active Canadian Pacific Railway. Both structures required the flexibility of a self-spanning system since traditional shoring towers could not be used. The Doka Girder form system offered the ability to span the fast flowing river while forming the four pier caps high above the river itself. There were two different types of pier caps to be formed on the bridge structure. The pier caps ranged in size from 1.42 m deep x 1.90 m wide x 24.43 m long to 2.7 m deep x 3.05 m wide x 24.40 m long. The system was then reconfigured to form the Canadian Pacific Railway Bridge using two pier caps of 1.83 m high x 1.50 m wide x 41.80 m long.
Flatiron faced environmental concerns of the surrounding area including a fishery, wildlife, and sensitive land. The Doka Girder system allowed for a minimal impact as it was suspended above the water crossing, not through it. The Canadian Pacific railway crossing also was required to be built adjacent to an active critical railway corridor that could not be disturbed. This limited access was a challenge and extra planning was needed to provide for the ability to construct without shoring towers due to the water and active railway.
The flexibility of the girder system allowed Flatiron to erect and strip the forms in smaller sections, which saved on the added cost of using a much larger crane. The safety of their employees, clients, subcontractors and the public was Flatiron’s number one core concern. Flatiron adhered to all Doka safety procedures as outlined and also attached a lifeline to the bottom of the Doka Girder panels to allow access to underside of pier caps, providing 100% fall protection.
“For the Donald Bridge Project the versatility of the Doka pier cap formwork system was beneficial as the access below the pier caps was restricted by the Columbia River and steep work area and transport the assembled system to the pier. The modular system allowed for quick erection as well as efficient removal of the formwork system,” said Rick Morrison, Project Manager, Flatiron Constructors Canada.
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