Masonry arch bridges are one of the oldest forms of bridge construction and have been around for thousands of years. Brick and stone were the original materials used and these bridges have proved to have a high level of durability, as most of them have remained serviceable after hundreds of years. In contrast, many bridges built of modern materials have required extensive repair and strengthening after being in service for a relatively short part of their design life and subsequently unable to meet current European loading standards [1][2]. This paper describes the development of a flexible concrete arch system that has virtually no embedded steel and can be constructed without centring thereby providing a highly durable and cost effective structure.
Masonry arches are strong, durable, aesthetically pleasing and largely maintenance free, yet since 1900 there has been a dramatic decline in their use. However, designers, contractors and clients now have access to a new method of constructing arches incorporating precast concrete voussoirs interconnected via polymeric reinforcement and a concrete screed. No centring is necessary, as the FlexiArch, when it is lifted, transforms under the forces of gravity into the desired arch shape. After discussing general aspects of innovation, the basic concept of the arch bridge system is presented along with technological advances since it was patented. Experiences gained from building over 40 FlexiArch bridges in the UK and Ireland and from model and full-scale tests carried out to validate the system during installation and in service are described. Thus under load the system behaves like a traditional masonry arch and existing analysis methods can be used for design and assessment.
The 1840's Teewell Hill arch bridge, in the suburbs of Bristol, was no longer adequate for increasing local traffic levels and needed to be widened. Several widening options were considered and it was concluded that the innovative FlexiArch would best accommodate the complex geometry of the existing structure whilst minimising social and economic impacts. In order to elegantly accommodate the raked spandrel walls of the existing bridge Macrete and WSP | Parsons Brinckerhoff worked collaboratively to produce a custom designed high quality precast concrete 'FlexiArch' which matched the contours of the existing bridge. As the FlexiArch system has no corrodible reinforcement, it is highly sustainable and will result in reduced maintenance as for the existing bridge. The elimination of centring and speed of construction (hours not months) minimised disruption to road traffic and to cyclists on the cycle network below the bridge-a key project criterion required by the client. Thus, in addition to addressing an accident black spot, the FlexiArch solution provided South Gloucestershire Council (the client) with an aesthetically pleasing and fully functional solution at a competitive cost.
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