Fenchurch St. Station, London UK Repairs to signal gantry

Railtrack anticipated a shut down of 6 weeks with other systems, the CINTEC proposals, required only 2 days.

Fact: The need for an efficient and effective road transport system is an essential feature of any modern economy. As the load carried by transport vehicles increases so also does the strain placed on bridges.

Fact: In Europe, the European Commission has published a Directive which requires all trunk road bridges to be capable of carrying a minimum of 40 tonnes from 1st January 1999.

Fact: In the UK alone, there are some 40,000 masonry arch bridges some of which are hundreds of years old and are in need of strengthening and repair.

Fact: ARCHTEC offers a one-stop-shop complete design and installation service utilising state-of-the-art technology and drilling methods.

Cavity Lock Systems, joined in the UK with Civil Engineers Gifford and Partners, and Rockfield Software, to develop and test the ARCHTEC strengthening technique at TRL (the Transport Research Laboratory) based near London. TRL has been engaged in an intensive programme of research and tests to provide data about the mechanism of collapse properties. Based on the evidence of such research, Gifford developed modelling strategies to predict a bridge's ultimate strength and failure mechanism. By using Rockfield Software, an advanced discrete element technique (never before applied industrially to bridges) is used to accurately simulate the behaviour of bridges. This technique overcomes the difficulties experienced by conventional analysis.

The test bridge was constructed without spandrel walls but, utilised steel containment walls not connected to the arch barrel to enable fill to be placed and compacted in the normal way. Before reinforcement, the maximum load for the arch was 20 tonnes. The test load was applied as a live-load at 1/4 span length which is known to be the most critical form of loading.

The loads were increased in increments of 1 tonne, as the loads increased crushing was observed, leading to the first hinge at 28 tonnes. The strengthening prevented the hinge forming under the load-line and delayed the formation of further hinges. Loading continued and further hinges formed around the load-line. The arch ultimately failed at 41 tonnes - the anchors had more than doubled the load-bearing capacity.

The load was removed allowing the arch to spring back thus demonstrating the elasticity of the system. By switching to displacement control the arch was loaded to collapse which occurred after a total vertical movement of 200mm at the load-line. Incredibly, whilst the bottom ring, fell off the structure, the rest of the arch remained held together by the anchors.