Llantysilio Chainbridge restoration

Chain bridge restoration project at Llangollen, Wales, UK. Ramboll

Chain bridge restoration project at Llangollen, Wales, UK. Ramboll

Contact

Laura Matthews. Ramboll

Laura Matthews

MEng (Hons), Principal Engineer
Fay Newham. Ramboll

Fay Newham

CEng, MICE, BEng, IHBC, Project Associate
Ramboll. Andy Marginson.

Andy Marginson

BSc (Eng), Head of Bridges, North

Thought to contain the oldest wrought chain links in the world, this bridge project has transformed a derelict and unsafe site into a safe, functional structure that is a major tourist attraction.

After painstaking restoration works designed by Ramboll and carried out by Shemec Ltd, the historic chain bridge crossing the River Dee between Berwyn and Llantysilio re-opened to the public in 2015 after safety concerns forced it to close in the 1980’s.

Linking communities

The bridge links two communities and is jointly owned by Llangollen Town Council and Llantysilio Community Council. A pathway from Berwyn railway station, now part of the Llangollen Railway, leads under a subway and down to the bridge and to the Chainbridge Hotel on the other side.

Historical significance

The significance of Llantysilio Chainbridge is widely recognised and acknowledged. It is described as 'a landmark of a crucial part of British engineering history' by the Royal Commission on the Ancient and Historical Monuments of Wales and is included in the Institution of Civil Engineers’ database of historically important engineering structures.

The distinctive bridge is of vital importance to the area’s industrial history and is a key attraction in the Pontcysyllte aqueduct and canal world heritage site. Horseshoe Falls, the source of Llangollen Canal, is a short walk from the bridge. Horse-drawn boats still carry passengers along the canal.

First chain bridge 1817 – 1870

The bridge was first built in 1817 to link two major transport routes in North Wales, the Llangollen Canal and the London to Holyhead Road. Local entrepreneur, Experius Pickering, wished to take advantage of the canal to transport his goods of coal, lime and iron bar, thereby giving him quick cheap access to the markets in the North. To achieve this he spent considerable time from 1814 onwards petitioning the Llangollen Canal Company to improve the feeder section of the canal and allow him exclusive access to the wharves and bridges. Ultimately, the construction of the bridge allowed him to monopolise the coal trade in the area.

Second chain bridge 1870 – 1928

By 1870, the bridge had fallen into disrepair and was dismantled. In 1876, Henry Robertson railway engineer and owner of Brymbo Ironworks near Wrexham, rebuilt it using the original chains. His design was similar in style to the first bridge although the new supporting posts were of iron rather than oak.

In 1928 a flood swept away most of the second bridge, with only the chains remaining.

Third chain bridge 1929 to date

In 1929, Robertson’s son Sir Henry Beyer Robertson, had the structure re-built as a footbridge to a design inspired by Thomas Telford’s Menai Suspension Bridge.

This third (and current) bridge comprises a two span chain suspension bridge carrying a footpath over the river Dee between Berwyn Station and the Chainbridge Hotel. One span crosses the river and spans approx. 24m and the other spans approx. 9.7m over a bedrock outcrop.

This bridge is supported by simple iron-frame towers. One is constructed on an abutment on the north bank, the other on a masonry land pier to the south. Having no river piers, the new design was a great improvement, being of greater strength and less affected by floods.

Six of what are believed to be the original chains, three on each side, have been re-used as the suspension 'cables' from which the deck is hung, while two more chains provide added rigidity beneath the deck. They are the oldest known wrought iron suspension chains remaining in use.

Consents, contracts, funding and support

As the River Dee is a designated Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC), all the works carried out over the river and its banks required consent from Natural Resources Wales.

To the North of the bridge the suspension chains are anchored into the rock cutting above the Canal. The Llangollen Canal is a World Heritage Site and as a result all of the canal, embankments and cuttings from the Horse Shoe Falls through to Chirk are classed as a Scheduled Monument. Therefore even though the bridge itself is not designated, the scheme required Scheduled Monument Consent from CADW.

Refurbishment works were designed by Ramboll and the contract awarded to Shemec Ltd under NEC Option C. The contract was approached in a collaborative way with all parties working closely together to ensure the project’s success.

Project funding was secured by Llangollen Town Council & Llantysilio Community Council from the Heritage Lottery Fund, WREN, Denbighshire Council, Cadwyn Clwyd and the Clwydian Range and Dee Valley AONB.

Cooperation and support from the Chainbridge Hotel, Llangollen Railway, Canals and Rivers Trust, local residents and businesses were also key to the success of the project.

Modern methods for assessment and design

Ramboll engineers made a 3D non-linear analysis of the structure and this helped to decide that any chains with a section loss greater than 60mm2 had to be replaced.

The analysis also determined that the deck could be opened for a pedestrian load up to 1.5 kN/m2. Whilst this is less than current design standards would require, it was agreed with Llangollen Town Council that this reduced load capacity was acceptable, considering the remote location of the bridge and its width. Warning signs were placed at each end of the bridge to restrict the number of people on it at any one time.

Ramboll designed the refurbishment works and new parapets to retain the appearance of the 1929 bridge as closely as possible, whilst taking into account the requirements of modern safety standards.

Dismantling, restoration and reconstruction

The scope of the restoration works included:

  • restoring and repairing, or replacing each iron element
  • a new timber deck
  • a new handrail system

Each metal element of the bridge was labelled and then the bridge was dismantled by roped access over the river span, with a scaffold erected over the dry span, and a separate scaffold over the hotel and canal.

A series of cables was drawn between the stanchions and the North Canal bank. One set of cables was for stabilisation and to take the load when chains from the bridge were removed. The other set of cables were for the roped access operatives, to support the hotel water-main and to support the dismantled bridge elements which were pulled to the bank for processing.

The decayed wooden decking was removed first, followed by the deck hangers, bracing and diagonals.

The bottom chains over the dry span scaffolding were disconnected at the stanchion and laid down on the scaffold for dismantling and processing. The bottom chains over the river span were supported at every other link to the roped access cables, disconnected at the north and south bank and pulled across the river to the south bank on to the scaffolding for dismantling.

Tension was taken out of the top chain backstays over the hotel and canal using a pulley system. The connection to the north stanchion was removed before chain backstays were lowered on to the scaffolding and dismantled. A similar process was used to dismantle the dry span top chains. The top chains over the river were supported at every other chain link before being disconnected and winched to the scaffolding above the hotel to be dismantled.

The stanchions and anchor points were refurbished insitu.

Once dismantled all the elements of the bridge were transported to the workshop by the local Welsh Highland Steam Railway. In the workshop the elements were stripped of paint, dirt and corrosion using traditional methods before being assessed for repair or replacement. The elements which were deemed too corroded to be repaired were sent to the local Museum in Llangollen and replacement elements were forged from mild steel. All the bridges elements, old and new received a flexiblised epoxy paint system.

When all the metal elements had been restored, the bridge was reassembled by returning each part to its original position.

The bridge was re-erected using the same methods as dismantling but in reverse.

Conclusion

Careful construction techniques and traditional methods were applied to conserve as much of the existing wrought iron elements as possible.

However, the ingenuity and innovation of modern civil engineering techniques were required to restore this historic structure to a serviceable condition.

Ramboll

Ramboll
240 Blackfriars Road
London SE1 8NW
United Kingdom
Tel: +44 20 7631 5291
Fax +44 845 299 1610

Mail: london@ramboll.co.uk

Company registration

Company registration

Ramboll UK Limited. Registered in England & Wales. Company registration no. 03659970. Registered office: 240 Blackfriars Road, London SE1 8NW


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