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National Highways has sanctioned the use of a new Swiss variant of expansion joint that has not been used in the UK before.

A large expansion joint on the River Nene viaduct, between junctions 12 and 13 of the A14, needs to be replaced having reached the end of its working life. The new joint is designed to reduce noise, make future maintenance easier and enable motorists to continue using the road while the repairs are carried out.

The work, to be undertaken by highways specialist Route One Infrastructure, is expected to take three months but to keep the road open as much as possible, innovative bridging plates are being installed spanning the excavated area, which can be raised to allow access for overnight working and lowered for traffic to flow in the daytime.

Without using these temporary bridging plates, which are winched and locked into place during the works, the route would need to be closed to all traffic 24/7 for several weeks.

One of the features of the new expansion joint is a quick release system so it can be replaced overnight should the need ever arise, significantly reducing disruption. It also has noise reducing plates to lower the noise created by vehicles driving over it.

The joint is a modified Tensa Modular LR-LS system, including the use of noise reducing sinus plates, manufactured by Mageba in Switzerland.

These types of bridge joint are used on long span bridges in the UK and across Europe, known as part 8 joints, in reference to the associated European Technical Approval Guidelines (ETAG) chapter.

The joint is designed by the manufacturer in accordance with Eurocode design standards for bridges as implemented by National Highways鈥� Design Manual for Roads and Bridges.

As explained by National Highways, the joint consists of a number of transverse lamella beams that support the rubber seals between, given the joint it鈥檚 watertightness. These lamella beams are supported from longitudinal beams supported between the bridge deck and the abutment that are designed to provide movement and rotation in all three directions. The joint uses specially designed low friction and highly durable bearings between the both the beams and the bridge interfaces to accommodate all deck movement without transferring horizontal forces into the structure.

The joint spans a 400mm gap, with a maximum design longitudinal movement of 243mm, preset at 50mm between rails at 14C for installation. All of the joint steel components are hot dipped galvanised to 140 microns minimum thickness prior to assembly for very high corrosion protection.

The Nene Viaduct joint has two particular modifications that make it different from usual:

• the addition of sinus plates above the lamella beams to both reduce noise and improve ride quality (avoiding the familiar clunk of driving over expansion joints).
• an integral 鈥楺uick-Ex鈥� system that allows the joint to be removed and replaced without affecting the remainder of the bridge structure.

The 鈥楺uick-Ex鈥� removal system comprises a 鈥榮econd skin鈥� provided at interfaces with the receiving structure, with the modular joint bolted into this additional steel interface. The second skin is cast in contact with the receiving structure.

During future replacement or maintenance of the joint, the second skin will remain in position as a casing, allowing the joint to be removed by unbolting. This add-on 鈥淨uick-Ex鈥� system has not been used in the UK before and is supported by innovation funding. The initial costs are approximately 10% of the joint fabrication and purchase costs, with no additional increase in associated installation costs.

The joint is fabricated in steel and cast in concrete into the original concrete bridge deck. In addition to the above, careful consideration has been undertaken in the design of the joint to address steel fatigue issues arising from the cyclic loading nature of road traffic that have previously plagued the durability of this type of joint.

The system was proposed by Mageba, the joint manufacturer, which is keen for this to be adopted UK-wide given the potential savings for future maintenance in both traffic disruption and installation costs for replacement joints.

The joint is a replacement for a modular reinforced rubber pad join with central bridging plates and side bearing elements of vulcanized rubber on steel plates, which required significant ongoing maintenance and caused difficulty in obtaining replacement components as these became obsolete.

The new joint has a design working life of 50 years, with the minimum period before major maintenance of 25 years and minor maintenance of 10 years. Minor maintenance is expected to be limited to the replacement of seals and similar minor elements that do not require significant disruption to traffic to replace.

Work on the scheme will start on Friday 29^th August, starting on the eastbound carriageway, and then switch to the westbound carriageway until the scheme is completed in December.

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