The Suir River Bridge
Introduction
Bridges are prone to harsh environmental conditions, increased traffic and loads among other physical mechanisms. Additionally, deferred maintenance contributes, majorly, to the deterioration of these bridges. For these reasons, therefore, it is important that every existing bridge is constantly subjected to assessments to determine its condition. This is important in order to determine and develop the bridge’s rating regarding the load it can hold and subsequently strengthen it to withstand more load to meet the ever increasing demands. An assessment is also fundamental in determining whether the bridge ought to be posted for the sake of public safety. While such an assessment could be carried out as a matter of routine practices; sometimes it is prompted by a change in the traffic flow, concern on suspected faulty construction materials after the completion of the bridge, discovery of a construction or design error or damage after being exposed to heavy loads (Wang, et al., 2009, p. 2).
Posting of a bridge poses dire consequences to the economy of a state and in as much as possible, it is important to monitor the bridge through load testing, analysis or both and the most common procedure for assessing an existing bridge is by structural analysis. Perhaps it is preferred due to the fact that it is the most economical. The structure of the bridge determines how resistant it will be with its capacity being dictated by how strong its components and their connections, are. According to (Wang, et al., 2009, p. 3), the strength of a bridge is, to a very large extent, determined by the properties of its materials including the strength of the materials, their elasticity modulus, chemical composition and their cracking stress.
The Suir River Bridge
The Suir River Bridge is hailed as the longest bridge in Ireland. This cable-stayed bridge was constructed as the centre piece in the 600 million pounds Waterford city’s bypass project in a bid to decongest traffic in the old Viking city (O'Sullivan, 2009, p. 509). Waterford joint ventures, composed of BAM, formerly known as Ascon and Dragados were mandated to construct an international project in terms of its diversity and scale across River Suir, only 2km west of Waterford city. Also, in addition to the state of the art cable-stayed River bridge the contractors were expected to construct 30kms standard roads, 18bridges, road junctions among other smaller scale projects (O'Sullivan, 2009, p. 510).
The Suir River bridge is located close to the defunct railway that was constructed at the commencement of the 20th century. The juxtaposition of these two architectural structures, one built in 1906 with steel and cast iron and the other one, a century later, made of gleaming cable is a clear representation of the major steps architecture has made towards advancement in not just the design and the scale, but also in the materials used for construction in only a century (O'Sullivan, 2009, p. 511).
In the contract, the tentative completion date for the multimillion pounds project was the year 2010 but, the contractors were able to complete it in 2009, barely three years since its commencement in 2006, with their pride being the 465 m bridge that was built across River Suir, joining Kilkenny to the north to Waterford city on the southern side. It marked the longest ever constructed river span in Ireland and the tallest ever; cable-stayed bridge. The bridge has four lanes, two in each direction, with a whopping 230 metres of the bridge span across the river, 91.5 metres of two back-spans and 77 metres of end spans. The bridge also has a beautiful 118 metres pylon that resembles an inverted letter Y from its base to the beacon top. It is undoubtedly the tallest, bridge, structure in the Republic. The deck of the bridge is supported by cables made of steel that radiate from the pylon that was also constructed on a peninsula that the contractors were able to reclaim from the southern edge of the River Suir. These cables were anchored in different places on the pylon and along the road deck which appears suspended. The configuration of the cables is strikingly symmetrical on both sides of the pylon (O'Sullivan, 2009, p. 3).
Bridge design and structure
The Suir River Bridge was designed by Carlos Fernandez, consulting engineers based in Madrid; the same engineers that designed the Bay of Cadiz Bridge. The construction of the bridge commenced in mid-2006. The first thing the engineers did was to reclaim the peninsula on which the foundation of the pylon was to be erected. This they did by filling in the selected section of the river, on the southern shore, selected quarry materials to up to about 12 meters. They then placed 1.5 metres of concrete on the base which provided a stable foundation for the pylon, whose actual construction began in early 2007 using micro piles, an innovation that had not been used in Ireland before (O'Sullivan, 2009, p. 6).
According to the contractor, the choice was informed by the fact that micro piles were more resistant in comparison to the conventional bored piles. Additionally, deploying the latter piles would have required that the splay of the pylon legs be greater and the pylon taller which has an impact on the cost and duration of construction. Micro piles were also preferred in the construction of the abutment on the north and pier, and on the crane’s foundation with the conventional bored piles, that have a larger diameter, were only installed just under the piers of the bridge and the southern side’s abutment (O'Sullivan, 2008, p. 630).
The Pylon
The River Suir Pylon, resembling an inverted letter Y is the most dominant feature of the Waterford city’s skyline. It is made of concrete, right from its foundation to the level of the deck. From the deck, the pylon’s legs are hollow with a 620 mm thickness inner diameter and 1390mm external diameter, all the way up until they merge, 66metres later. The walls of the pylon vary in thickness and profiles which could rise to 15 degrees. Additionally, the legs of the pylon lean towards each other with the distance between them reducing as their weight increases with the increased height. For these reasons, there was need for the contractors to ensure that the fundamental setting out was accurate in addition to incorporating a bracing system that would minimize the deflection of the pylon legs causing bridge instability (O'Sullivan, 2009, p. 4).
The Bridge’s deck and cables
The Suir River Bridge’s deck is a steel and concrete structure, about 1.8 metres in depth and a width of 26 metres. It looks like a ladder, horizontally laid and supported by an abutment and the on-land piers on the southern side, the state-of-the-art pylon in the peninsula and an abutment and the third pier on the northern side of Suir River. The erection of the deck commenced in August of 2008 and it started from the Pylon towards the dry land. The engineers felt that the piers could not hold the weight of the deck and therefore installed temporary trestles to support the deck. The cables that form a beautiful semi-fan arrangement were connected to transfer loads through the pylon. The bridge has a total of 76 cables radiating from different points of the pylon. They range from a diameter of 355mm to the widest being 455mm. The cables were connected at a 10m interval along the ladder-like deck (O'Sullivan, 2009, p. 8).
Lighting and Finishing
The bridge’s pylon, the setting of the river and the need to ensure that the bridge is efficiently and effectively lit have influenced the lighting system to a large extent. The degree of innovation used by the engineers to light up this bridge is highly laudable. They were able to make the beautifully engineered architectural details of the pylon the source of the bridge’s lighting by one; running a strip of lighting at the point where the two legs of the pylon intersect and two; lighting the inside walls of the pylon’s legs both below and above the deck (O'Sullivan, 2008, p. 631).
The bridge is a sight to behold. In addition to its functionality, the engineers ensured that they succeeded in sneaking in beautiful finishes to the project; the deck, the pylon and the piers that were essentially made to support the bridge. The pylon’s legs, for example, look a lot like a ship’s prow and the pylon is in itself, endowed with beautifully curved lines. The engineers, on completing the construction of the bridge, sprayed its deck with a product that made it waterproof. The completed project added a feather to the innovation of civil engineers and, upon its official opening in October 2009, the Suir River Bridge provided the missing linkage in Ireland’s infrastructure (O'Sullivan, 2009, p. 10).
BIBLIOGRAPHY
O'Sullivan, E., 2008. Record Breaking Bridge Reaches Construction Milestone. Engineers
O'Sullivan, E., 2009. Ireland's Longest Cable-Stayed Bridge Reaches Completion. Engineer's
O'Sullivan, E., 2009. Single Concrete Pylon Supports Ireland's Longest Cable-Stayed Bridge,
Waterford: Construction & Civil Engineering Department, Waterford Institute of Technology.
Wang, N., Ellingwood, B., Zureick, A.-H. & O'Malley, C., 2009. Condition Assessment of
Existing Bridge Structures, Georgia: Georgia Institute of Technology School of Civil and Environmental Engineering.
