ICE - Institution of Civil Engineers - Virtual Library

Mizen Head Footbridge in County Cork, Ireland, is a reinforced concrete through-arch structure spanning 50 m. The structure is 95 years old and exhibits typical reinforced concrete defects of spalled concrete, cracking and staining from reinforcement corrosion. An inspection, geometrical survey and a series of material tests were carried out as part of an assessment of the bridge. Petrographic examination of samples removed from the structure gave confidence in the quality of the concrete in the structure. Determination of carbonation and chloride levels in the concrete identified future repair strategies for the structure.

Rehabilitation of concrete structures using advanced composite fibre-reinforced polymer (FRP) materials has rapidly gained momentum due to the economic and structural benefits offered by such solutions. In 2000, The Concrete Society published its technical report TR55, the world's first best practice guidance on strengthening concrete structures using advanced composite materials in line with British design codes. This document has gained acceptance nationally and in many other parts of the world. Due to the rapid evolution of strengthening techniques, materials and theoretical models of behaviour, the guidelines have been updated for publication in 2004 in order to reflect the current state of the art and best practice. In particular, the chapters dealing with flexural, shear and column strengthening have been substantially revised to reflect latest research findings. Details of the main proposed changes are given in this paper. Design guidance on the use of new techniques such as near surface-mounted (NSM) reinforcement, prestressed FRP and anchorage techniques have also been introduced into the guidelines and are summarised in the paper. The design aspects are backed up with examples of the latest applications of the various strengthening techniques and materials.

Heyeswood Railway Bridge was constructed in 1958 and carries the A556 dual carriageway over an over-head electrified spur of the West Coast Mainline railway. The 45° skew deck comprises fabricated steel girders with reinforced concrete slabs at the top and bottom of the deck, forming a complete enclosure. The bridge had suffered deterioration as a result of a variety of factors resulting in significant spalling to both slabs. Interim strengthening was carried out in 1991. Major utilities were very restrictive. The most cost-effective long-term solution was to over slab the top slab, nominally repair the bottom slab and provide a unique load-carrying, glass-reinforced plastic enclosure to the soffit. This aspect of the design is emphasised. The top slab strengthening was carried out in two phases, enabling a contra-flow traffic system to be in place throughout. Work to the soffit had to be carried out under a series of Saturday night railway possessions. The project was carried out as part of the Highways Agency's innovative Construction Management Pilot. It is unlikely that this project could have been successfully concluded under a traditional, more adversarial contract.

The road network in Ireland comprises national primary and national secondary roads, and non-national regional roads and local roads. Since 1994 the responsibility for the management and maintenance of the national roads has rested with the National Roads Authority (NRA). In 2001 the Eirspan bridge management system was introduced to coordinate and integrate activities such as inspections, repairs and rehabilitation work to ensure optimal management of the national road structure stock. This paper summarises the reasons for the introduction of the system and gives a review of the distinct activities included in Eirspan. It describes how bridge components are condition rated within principal inspections and outlines how, after the completion of the inventory gathering and first principal inspections, repair works are priority ranked. Future developments within Eirspan are also discussed. Eirspan helps engineers within the NRA to prioritise maintenance needs and maximise the use of available funding. It has proved to be an invaluable tool in helping to maintain the function and safety of bridges throughout the national road network in Ireland.

When assessing the safety of existing structures it is often not economic to use the design codes, which may be rather conservative in nature. In this paper, safety is measured in terms of the factor of safety, defined as the ratio of available strength to total load effect. The paper examines the sensitivity of the safety factor of two example concrete slab bridges to: (1) the method of structural analysis and failure criterion; (2) the inclusion of updated strength information; and (3) the application of site-specific loading. It is shown that in certain cases plastic analysis methods can predict the ultimate load capacity more accurately than conventional elastic analysis. Methods are suggested for calculating the material strength values based on test results so as to better reflect the true in situ strength of the bridge. Finally, the use of a bridge-specific load model is suggested which may lead to an increase of the factor of safety.

This paper sets out the key aspects of the planning, design and construction phases of the refurbishment of Berwyn Viaduct at Llangollen Railway, together with details of the construction of the replica cantilever platform to replace the structure removed following the Beeching cuts in the 1960s. It details how close liaison was required between the client and contractor to ensure the successful conclusion of the project on time and within budget.

Windsor Branch Railway Bridge carries the busy M4 motorway over a mainline railway and two public footpaths. The route forms the main link from London to South Wales and the south west of England. Constructed in the early 1960s, the bridge consists of five simply supported skewed spans each comprising precast, prestressed concrete beams. The deck is divided longitudinally into two halves by a covered central reserve light-well. A risk assessment identified the bridge as requiring high containment barriers to protect the railway line below. Unfortunately, it was not possible to install these barriers without additional structural strengthening. This paper discusses the use of ground anchors to restrain the wing-walls and capping beams against the collision loads imparted on the structure by the high containment barriers.

This paper provides an overview of the performance of repairs made to concrete bridges in the field and subjected to the actions of traffic and weathering. Data have been obtained from some 70 case histories having repair lives of up to 33 years on bridges aged from 1908 to the 1990s. It was found that only 45% of the repairs were reported as being wholly successful when last inspected. Perceived causes of failures are considered and ways of making more durable repairs are outlined.