Peri's LGS delivers bridge ahead of schedule

The Skanska-NDI Joint Venture has used formwork manufacturer Peri's weather protection system to help deliver a new bridge across the Vistula River, Poland three months ahead of schedule.

The bridge, which is known as MA-91 (Most Autostrady Nr 91), is the 91st constructed since the project started in Gdansk in October 2005.

Located 1 km south from Grudziadz it is part of Poland's A1 Autostrada, itself part of the priority E75 North-South Trans European Network (TENs) corridor linking Vardø in Norway to Sitia on the Greek island of Crete via Finland, Poland, the Czech Republic, Slovakia, Hungary, Serbia and Macedonia.

The 568 km long Polish section of the E75 will eventually run from Gdansk through Torun, Lódz, Czestochowa and Katowice to Gorzyczki, where it will cross the border into the Czech Republic and connect with the D1 motorway.

The bridge and access roads total just under 2 km, while the bridge is 400 m-long. The access road from the north is about 1 km-long and the access road from the south is about 600 m. Peri's LGS (lattice girder system) is installed at the access road in the south.

Here the bridge is being constructed incrementally using a 25 m-long formwork system. Individual sections are concreted together, hardened and then raised a few millimetres before being pushed into place.

The LGS temporary weather protection system, which is based on the Peri Up modular scaffolding system, spans the complete working area and allows weather-independent construction of the individual sections for the bridge's superstructure, one of the main factors that influenced the Skanska-NDI Joint Venture into renting it. The benefit has been round the clock working that has seen the JV shorten the construction period by three months.

Concrete construction

For the concreting work of the bridge's hollow box profile, a construction time of 12 months was planned for. With work starting in November 2009 and the casting crew had to endure temperatures as low as -25°C during the winter months.

To protect against these extremes the JV looked for a low-cost way of protecting its work force. Working with Peri's engineers in Płochocin, Poland and Weissenhorn, Germany the JV decided to use the LGS.

There are four structures in total. The two smaller, permanently installed "tents" are used for reinforcement work preparations, while the two, larger movable "tents" span the formwork and concreting areas.

However, to ensure unhindered material deliveries and concrete installation, Peri's design means the LGS is moveable. The girder supports are equipped with rails and extend over a length of 55.5 m, twice the LGS.

Special requirements

Finding space for the LGS on the cramped site was just another problem to overcome for the JV, especially as the available space between the formwork for both lanes of the bridge was very limited.

Load transfer of the support construction of both weather protection roofs had to be guaranteed via a common central support: a challenge for the planning as the high loads can cause large deflections to the construction, which could make moving the roofs on the rails difficult.

It therefore meant ensuring that resulting loads and deformations were accurately calculated during the planning phase and execution. The wind loads could be transferred through serial components. In order to secure LGS against lifting, the support plates were ballasted and, in part, anchored in the bottom slab.

With Keder track and sheeting, the LGS's scaffold construction resulted in very light and translucent roofs. The solution also included a side and gable covering. Overlapping of the sheeting at the joints ensured a tightly-fitting enclosure, which at the same time could be easily opened, and with the extremely low outside temperatures, the "tents" were also heated.

Thanks to the LGS, the site team was able to continue all working operations without any stoppages. This resulted in enormous time savings, helped by the fact that the LGS could be moved by just two or four people without the need of additional equipment, such as a crane.