Carbon fibre and composite strengthening of Minsterley Bridge in Shropshire, UK

Abstract

Minsterley Bridge is the oldest reinforced concrete bridge in Shropshire, UK. The now listed structure was built in 1909 to the design of L. G. Mouchel, carrying the B4387 road over the Minsterley Brook. This paper describes the strengthening and repairs, carried out in 2010, to achieve Highways Agency live load capacity. The bridge is a shallow arch 9ṡ1 m in span, acting partly as an arch and partly as a beam. The challenge was to assess what the arch capacity was, being governed by the lateral resistance of the ground to thrust. This resistance, provided by passive earth pressure, was considered variable as its magnitude depended on the movement generated by the arch thrust, requiring an iterative approach. Beam capacity was increased by the introduction of a shallow reinforced concrete saddle and carbon fibre on the soffit. The longitudinal shear connection of the saddle was identified as the overall constraint to the strengthened capacity. Accommodation works included diverting optic cables, and the provision of a temporary bridge on screw pile foundations. A public exhibition of the proposals and engagement with the local primary school are also described, culminating in a bridge-building competition to inspire the next generation of engineers.