Sustainability in action

A recent project in Germany shows how retrofitting well-designed shock transmission units can greatly enhance the ability of old highway structures to resist modern traffic loading, with little or no impact on structure users or the environment

The Bremer Damm, a highway in the German city of Hanover, is primarily situated on an embankment that elevates it above the surrounding city, facilitating smooth traffic flows by means of bridges along its length. One of these structures, built in 1959, is a 17-span prestressed concrete slab bridge with a total length of 360 m. With design braking forces according to the relevant German design code having more than doubled since the bridge was constructed, it was determined that this shortcoming needed to be addressed – perhaps by demolishing and rebuilding the entire structure.

However, a far easier solution to the problem was developed, primarily involving the use of shock transmission units (STUs, also known as lock-up devices, LUDs). These hydraulic devices to not resist slow-acting effects such as structural expansion/contraction due to temperature changes, but lock up for the purposes of shock transmission when sudden impact-type loading occurs. This temporarily changes the static design, distributing the loading longitudinally through a bridge like this and enabling it to be resisted by different parts of the structure, acting together. STUs are commonly used to protect structures from the sudden large forces that can arise in earthquakes, but are also used to distribute high braking and acceleration forces from road and rail traffic.

RESTON®STU shock transmission units were selected for use, and designed for a longitudinal force of 240 kN and a stroke of 250 mm. The use of these devices – which are virtually maintenance-free – to address the bridge’s structural deficiency was an excellent example of sustainability in action. With a minimum of effort and expense, and no impact on traffic, the service life of the structure could be considerably extended – conserving our built environment, saving natural resources, and minimising pollution from construction and from disrupted traffic.

Engineer: EHS beratende Ingenieure für Bauwesen GmbH
Contractor: Eurovia Beton GmbH
Bridge owner: Niedersächsische Landesbehörde für Strassenbau und Verkehr (Lower Saxony roads and traffic authority)

Design representation of a 3-gap TENSA®MODULAR joint as designed for the Queensboro Bridge

The bridge structures separate traffic flows and provide space beneath for parking etc.

The shock transmission units required by the renovation project enable large braking forces (today over twice the magnitude of those for which the bridge was designed in the 1940s) to be distributed longitudinally through the bridge, overcoming the deficiency

The RESTON®STU devices at each side of the structure span the gaps between the bridge’s otherwise structurally independent sections, at the same axes as its expansion joints

View of one RESTON®STU device as installed

The installation work, carried out by mageba Germany, involved challenging drilling of anchor holes in the reinforced concrete structure, grouting of anchor plates and adjusting of STU pre-setting as necessary