Strengthening a 285 year old narrow stone bridge to accommodate today’s highway loading capacity

Unsliven Old Bridge, Stockbridge

The client: Sheffield County Council

The 8.5m span Unsliven Old Bridge was originally built in 1730s as a narrow stone bridge for horses and pedestrians only. It was extended on both sides in 1796 to enable it to carry carts as well as horses.

The problem:

In circa 1980, a strip of stonework on the crown of the west arch extension was cut-out to accommodate an electricity cable in a 75mm diameter plastic duct, thus weakening the arch.

A reinforced concrete slab was cast on top of the west and centre arch to bridge a 40mm gap which had opened up between the west and centre sections of the arch. The slab also encased the electricity cable.

In 2013, the west and centre sections of the bridge were assessed as being understrength. It was proposed to replace the bridge but local residents were so outraged they successfully campaigned against this and Goldhawk was called in to install the MARS System to bring the bridge up to full capacity.

The Goldhawk solution:

It was found that, as the centre section had a relatively thin barrel, it could not be brought up to full strength using the MARS System alone. However, when the MARS System was combined with a lightweight foamed concrete fill, the bridge was able to be upgraded to accommodate full highway loading.

Bridge damage to the top slab requiring repair and bridge strengthening

Damage to the bridge

Exposed ducting and cabling installed in the 80s, causing damage and weakening of the bridge.

Bridge strengthening work and preparation near Sheffield

MARS system installation

Due to support from local campaigners the bridge required sympathetic strengthening and restoration.

The MARS bridge strengthening system by Goldhawk Bridge Restoration

Careful finishing at the underside of the arch

The MARS system combined with a lightweight, foamed concrete fill.

Bridge strengthening at Old Unsliven Bridge

Preserved history and heritage

An unrestricted bridge was delivered at a fraction of the environmental and monetary cost of a replacement.