Unusual Bridge Building Project

Case Study

“Without the high-performance software of RIB it would not be possible to make such complex calculations with so many system and cross section changes and over 850 load cases with the required accuracy within this time,”: Jürgen M. Sättele.
Assembly by lifting: Section 7 onto pier axis 50 and auxiliary pier 1.

Eckhard Held, Construction Engineer, R&D Structural Engineering, RIB Software AG

Germany’s Bundesstraße 1 (B1) federal highway runs in an east-west direction from the Dutch border near Aachen via the Potsdamer Platz in Berlin to the Polish border at Küstrin-Kietz on the River Oder.

At the Polish border, congestion in the village of Küstrin-Kietz is being eased by a bypass for border traffic. This involves building a new 564.5m composite steel bridge spanning the Berlin-Poland rail link, local roads and a stormwater canal of the Oder.

In November 2006, main contractor Züblin and other construction companies began work on the pile foundations. The steel construction was completed in January 2008 and the subsequent concrete works were finished in June 2008.

Precision job

Holzapfel, Rüdt and Partner, Consulting Engineers VBI in Stuttgart were contracted to perform the structural engineering. Manager Dr.-Eng. Jürgen M. Sättele and his team headed by Hanjo Krimmer, Construction Engineer, provided the exact static calculations required to begin construction work on the 10.5 million Euro bridge building project on schedule. This was no easy task in view of the difficult initial conditions: the bridge which is curved in plan and elevation and has eleven spans with a maximum span width of 73.00 metres goes over a flood protection area which must not be affected. The steel girder system therefore had to be built from both sides. The individual sections made of U-shaped, open steel trough cross section are assembled at the abutments and then pushed in the longitudinal direction of the bridge. The steel sections could only be lifted into position in the middle part.

The bridge is located in a bend with a radius of 800 m. The imposing structure has an overall width of 12.20 m. The course of the cross section is haunched in the area of the railway line. The construction heights vary between 2.40 and 3.40 m. Due to the soft cross section of the trough, a superelevation of the web plates of up to 400 mm is planned. As the two webs have different heights because of the transversal slope, there were differences in deformation and therefore superelevation differences between the webs of up to 30 mm. “We calculated each web separately,” explains Krimmer.

Challenging concreting work

The concreting of the bridge decking was also a complex procedure involving 33 concreting stages. To make optimum use of the cross section, concreting was done according to the step-back technique and, due to the initial conditions at the eastern end of the bridge, partly in a continuous process. The cycle time is a week.

To be able to take up the horizontal component from the concreting loads with the diagonal webs, horizontal tension ties have to be installed. The tension ties also have to be disassembled again to enable the 65-ton formwork carriage to move over the structure. “The load during concreting is immense,” reports Krimmer.

Maximal loads

To minimise the calculation work, the engineers chose a one-bar model – calibrated with a three-bar model for the static calculation. Deformations were calculated with the three-bar calculation model due to the web heights. The assembly of the 1600-ton steel girder system was mapped in simplified form with four construction conditions. The Stuttgart engineers simulated the production of the road slabs accordingly with 19 concreting states. In total, Sättele and Krimmer and their team did the calculation on both models with 28 primary and secondary construction conditions. The concreting conditions were extremely critical for the open cross section of the trough of structural steel S355, as it is torsionally soft at this time.

Another challenge for the structural engineers was the structural bearings, some of which were twisted, the curvature in plan and elevation of the system axis and the relatively heavy formwork carriage. As a consequence of the high load of the steel girder system, flange plate thicknesses up to 110 mm and web plates with closely spaced stiffener plates had to be installed. An equally difficult task was the exact determination of the superelevation curves in the webs, as the web heights on the left and right are different.

Software system for complex calculation methods

For calculation and bond dimensioning in the final state, the engineers at Holzapfel, Rüdt and Partner worked with RIB bridge construction software PONTI verbund. Besides loads of building construction in progress and permanent loads, 850 traffic load cases were used in the one-bar model in 25 structural conditions. Secondary effects also had to be taken into account. Bond dimensioning was designed according to the DIN report for all usual verifications in the limit states of load-bearing capacity, fatigue, suitability for use and bonding agent excluding buckling.

“Without the high-performance software of RIB it would not be possible to make such complex calculations with so many system and cross section changes and over 850 load cases with the required accuracy within this time,” Sättele sums up. “We’ve been using RIB software systems for many years for structural designs and measurements and they are particularly useful for complex construction projects.”

Industries>Architecture, Engineering & Construction>Architects and Engineers>Holzapfel, Rüdt and Partner

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