Monday 05.10.2020

Neckar bridge Benningen: The bridge is close to completion

In order to relieve the town center of Benningen as well as the old Neckar bridge and to equalize the traffic junction of the L 1138 Freiberg am Neckar - Marbach, the L 1138 is newly built as a bypass. The core of this approx. 1.20 km long bypass is the construction of a Neckar bridge, which crosses the river in a curved alignment, as well as an adjacent approx. 100 m long retaining wall. The design of the new Neckar bridge had to take into account, among other things, the new generation of 135 m long inland waterway vessels, which require a width of 60 m and a height of 6.3 m above HSW (highest shipping water level) in the area of the Neckar bend.

The 12.4 m wide and 195 m long steel composite bridge initially runs in a turning clothoid in plan before it changes to a constant radius R = 125 m. This is accompanied by a change in cross slope in the area of the beginning of the structure from -2.5 % to +7.0 %. During the preliminary and basic design, particular attention was paid to a harmonious fit into the surroundings, so that a composite bridge with dissolved haunches (with a certain resemblance to the Elbe Bridge Mühlberg) was chosen as the preferred solution. The semi-integral frame bridge with its distinct haunched superstructure and resolved skew stems is also a low-maintenance structure due to its monolithic connection to the foundations on the river piers. In addition, with spans of 54.5 - 86.0 - 54.5 m and an overall height of only 1.9 m in the center of the span, it was possible to design a slender structure (max. slenderness L/45).

In addition to the complex geometry, other special technical requirements had to be taken into account:

  • Horizontally flexible foundations of the river piers to reduce the constrained cut sizes à Conical design of the large-diameter drilled piles Ø1.5 m (two-layer reinforcement with longitudinal bars Ø32) in the upper area with steel pipes to achieve free movement of the pile head
  • Bending-resistant connection of the piles (tightly welded hollow boxes) to the so-called "stub piles" with concrete C60/75 SVB, highly reinforced (approx. 330 kg/m³)
  • Design of the superstructure as a tightly welded box girder with outwardly inclined webs, variable ground plan curvature and variable height

After construction of the foundations and substructures, the first sections of the superstructure were placed on auxiliary supports in the foreland area and welded in place. The river-side haunches, which were cantilevered freely in this stage, were initially connected to the land-side sections by means of auxiliary structures, without any intervention in the Neckar River being required.

For the bridge closure of the steel box girder cross-section, the missing middle section (sections 6+7) with a length of 145 m and cross-section dimensions of approx. 1.5 x 4 meters was moved from the pre-assembly site on the northern bank of the Neckar to its final position on Saturday, June 20, 2020, whereby the Neckar was closed to navigation in this area. A floating crane with a maximum lifting capacity of 200 t was required for the lift-in operation, which transported the 145 t bridge body the last few meters along the Neckar and placed it on the hydraulic presses.

Under the critical eyes of around 200 spectators, including some representatives of LAP, the action proceeded to everyone's relief without any critical incidents - the missing superstructure section fitted in perfectly and was temporarily secured in its position before the welding work in the two joint areas is carried out in the coming days. Subsequently, assembly of the cantilever bracket formwork for the deck slab will begin, which will support the up to 45 cm thick and 3.8 m cantilevered concrete slab in 11 concrete sections during construction. Completion of the bridge structure is expected in early 2021, with traffic opening planned for 2022.

Client:  Regierungspräsidium Stuttgart

Services by LAP:  Basic and tender design, detailed design and site supervision

Photos of the Construction Site:  PERI Vertrieb Deutschland GmbH & Co. KG