What is a viaduct?
A viaduct is a bridge that carries a road, railway or cycle path over another traffic route or over a valley. In Dutch it is also called a viaduct. The difference from an ordinary bridge lies mainly in what is underneath: a bridge usually spans water, a viaduct spans land or traffic. If a waterway is carried over a road, it is called an aqueduct.
In civil engineering a viaduct counts as a civil engineering structure (in Dutch kunstwerk), just like bridges, tunnels and locks.
Construction
In outline, a viaduct consists of:
- Abutments: the supports at both ends, which carry the deck and form the connection with the embankment.
- Piers or intermediate supports: intermediate supports on longer viaducts.
- The deck: the carriageway, often made of prestressed concrete beams or a concrete box section, sometimes of steel.
- Bearings and expansion joints: the deck must be able to expand and contract with temperature. Bearings allow this movement and expansion joints (such as a finger expansion joint) bridge the gap in the road surface.
Historic railway viaducts are often built of masonry with a series of arches. Modern viaducts are usually built in concrete, often with precast beams.
What to look out for
- Headroom: the clear height under a viaduct determines which traffic can pass underneath. When rebuilding or repaving under an existing viaduct, this height must not be reduced unintentionally.
- Maintenance and inspection: expansion joints, bearings and concrete cover are the known weak points. Leaking joints let moisture and de-icing salt onto the concrete below, with a risk of reinforcement corrosion.
- Noise and vibration: for homes close to a viaduct, noise protection is often a point of attention in the permit process.
Related terms
- Bridge
- Aqueduct
- Abutment
- Pier
- Arch bridge
- Civil engineering structure
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