Holger Glinde from Institute Feuerverzinken explains a new direction for bridge expansion joints in Germany.
Bridge expansion joints absorb the movements and rotations from the bridge superstructure. When they are built-in, only a small part of this complex construction is visible. As well as being subject to mechanical stresses, expansion joints are, most notably, exposed to corrosive environments, particularly chloride contamination from de-icing salts.
Robust and durable hot dip galvanizing provides a good corrosion protection solution.
While other countries have had some working knowledge of hot dip galvanized bridge expansion joints, in Germany, galvanized expansion joints were first used in 2016 following a decision by the North Bavarian motorway authority to introduce them for a bridge over the river Naab (Fig. 1 and 3). The 300 m-long bridge, near Pfreimd, forms part of the A93, which runs from Hof to Regensburg. Why are expansion joints important?
Why are expansion joints important?
Expansion joints are very important for a bridge because they allow:
- A bridge to expand and contract according to temperature changes
- Protect bearings that are holding up the bridge span Protect steel and concrete structures underneath the joints – that are holding up the bridge
- Protect steel and concrete structures underneath the joints – that are holding up the bridge
High-quality bridge expansion joints save money
As opposed to bridges, which are mostly designed with a life span of 100 years, within the additional technical terms of contract and guidelines for civil engineering works (German designation: ZTV-ING), the service life of a bridge expansion joint must be at least 50 years, for traffic category 1 in Eurocode EN 1991-2.
Bridge expansion joints must therefore be renewed at least once during the life span of a bridge. Data from Germany, Italy and Switzerland substantiate that life-cycle costs depend considerably on the quality of bridge expansion joints. A high-quality bridge expansion joint is significantly more economical over time, since fewer maintenance, repair and replacement costs are incurred. In comparison with a standard product, savings of more than 40% can be achieved over a 50-year period, based on life-cycle costs.
Defects from corrosion on bridge expansion joints
Corrosion is the most commonly reported cause of defects on bridge expansion joints. Improving corrosion resistance is thus, a major factor in attaining medium to long-term cost savings for bridge expansion joints. It is very important to keep in mind that components below expansion joints can be prone to high levels of corrosion and these need durable protection as well.
Corrosion is the most commonly reported cause of defects on bridge expansion joints. These defects can be avoided by using hot dip galvanizing as long-lasting corrosion protection; the service life of bridge expansion units can be improved and the life cycle costs can be reduced.