Focus of Doka's formwork has been the construction of the 127 m high main pylon which will dominate the skyline of Toledo, Ohio. The pylon's construction has been highly complex, with a transition in cross-section from an octagonal shape to a "gothic cross". The cross-shaped upper section enables the incorporation of a glass curtain wall on each of the four faces. An advanced array of LED lights will shine in unlimited color combinations through the 56 m tall glass panels.

The bridge is being built for the Ohio Department of Transportation by Fru-Con Construction, a division of Bilfinger Berger. Figg Engineering Group designed the main structure and the project management consultant team is lead by HNTB Corporation. It is the largest project ever undertaken by ODOT and, at US$280 million, the most expensive.

The cable-stayed bridge has a precast segmental concrete deck and a 373 m main section over the Maumee River. It will carry six lanes of traffic on the I-280 highway and will aid the passage of shipping by providing a high level fixed route in place of the existing drawbridge. The roadway will be up to 39,6 m above water level.

Doka formwork has also been used for the 197 octagonal piers, which each stand 38 m high. They have maximum dimensions of 7,3 m by 3,7 m.

European and US technology has been combined in the systems provided by Doka for the project. The project brings together Doka's Steel Girder system - popular in the USA - and the European platform and multiple lift concepts.

Virtually the full range of Doka USA's product line is used, including Top 50 formwork, Framax Xlife, Steel Girder, MF 240 climbing system and SKE 100 self-climbing system.

Doka produced the concepts and drawings for the formwork as well as carrying out the supply and providing an advisory presence on site during the casting operation. All systems were delivered within two months from the order being placed. "It was an enormous amount of formwork to design and build in such a short period, but we did it," says Dave Monnot, account manager.

"This was a strong engineering solution that delivered speedy results at an economical price," says Fru-Con's Warren Hallam. He welcomed being able to use a single supplier to handle all aspects of the work.

The pylon was built using a combination of systems that varied as the cross section changed. A lift of 60 m3 to 69 m3 was completed every 10 to 14 days for the lower octagonal sections. When work reached the upper pylon, the rate increased to a pour every four days.

As well as having a complex shape, further challenges came from the pylon's requirement to support a cradle system weighing more than 6 t. The bridge is one of the first in the world to have this type of stainless steel stay cable cradle system. The cradles keep the cables in separate protective tubes as they pass through the pylon. Tolerances for the pylon formwork were particularly tight as the cable penetration opening had to be accurate to within 1,6 mm.

The first two lifts for the pylon's octagonal lower part were formed with Doka's Steel Girder self-spanning steel form system, using both standard and custom components. The next three lifts had an added complexity as their corners had compound curves, with a vertical radius of approximately 42,98 m and a horizontal radius of 4,8 m. The Doka Top 50 system was used for this area and integrated into the standard steel girder.

The Steel Girder and Top 50 formwork components were fitted to Doka's MF 240 crane-handled climbing system which provides a 2,4 m-wide platform for safe working. MF 240 also makes provision for the formwork to be retracted by 750 mm to allow easy cleaning as well as fixing of the reinforcement.

This arrangement continued up to the eighth pour where the pylon incorporates cantilevered diaphragm deck units, formed using Steel Girder. "That was an amazing pour," recalls Dave Monnot. This level marked a transition from the octagonal form to the upper cross-shaped section. Custom-made steel and wooden units were used for the transition area.

The SKE 100 self-climbing system allowed multiple climbers to be combined to achieve the cross shape of the pylon's upper section. Use of SKE 100 also eliminated the need for a crane to move the formwork and created a safe working environment while enabling climbing to be carried out largely independently of the weather. The system was also able to cope with the difficulties of stripping and rolling back the forms for such complex sections.

The self-climbing system took the pylon to almost its final height, with the top section cast at ground level using Top 50 formwork and positioned by crane.

Six sets of formwork were used for the 197 piers. Rapid progress was achieved, with each set cycling two to three times in the six-day working week. The 197 piers were octagons of varying dimensions, from 2,4 m by 3 m to 2,4 m by 6 m. The wall thickness also varied, as did the height, from 44 m down to just 2,7 m. They were formed using a custom Steel Girder solution and MF 240. The "martini glass" shaped caps were cast using custom formwork.

As there was a wide range of pier heights on the project, Doka looked for ways of adopting some standardization. The MF 240 system could support the Girder form system to a height of 4,9 m. Each pier was give a starter pour to a height of between 2,7 m and 6,7 m, which enabled the remainder to be cast in standard 4,9 m rises using formwork which had already been mounted on the MF 240. Use of the platform-based system enabled material to be carried up to the next level without needing constant access to a crane.