Marcella Murphy explains the engineering challenges behind the building of the new Dún Laoghaire library and outlines how innovative features have been deployed in its construction, ventilation and energy conservation
Civil

The Central Library represents the biggest single investment by Dún Laoghaire-Rathdown County Council in a civic amenity. Under the 2004-2010 Dún Laoghaire-Rathdown (DLR) County Development Plan, the Central Library was envisaged as a crucial element of a programme of regeneration. The councillors agreed to proceed to an architectural competition and to make funding available for the Central Library at a meeting in 2006. The Royal Institute of Architects of Ireland (RIAI) organised and ran the competition. The design by architects Carr, Cotter and Naessens was the winning entry and the unanimous decision of the jury.

In accordance with Part 8 planning, the plans for the Central Library were put on display in 2009 and 33 submissions were received and considered. A recommendation was subsequently made to proceed with the development. Carr, Cotter and Naessens assembled their team, which included structural engineers Horgan Lynch, mechanical and electrical engineers Arup and landscape architects Atkins. The main contractor was John Sisk & Son (Holdings) Ltd and the client was Dún Laoghaire-Rathdown County Council (DLRCC).

DLR Lexicon concept


Moran fdinal

Moran Park pond before reconstruction

The building form was to be kept low by using the entire length of the available site. The building is lower at the end of Moran Park, so as not to compete with the Royal Marine Hotel. The seaward end of the building tapers up and in, to form a grand window overlooking the harbour and beyond to the Irish Sea. The materials used for the building were selected to match those already in use in the town. The building is generally clad in granite, similar to the original Dalkey granite used in the walls, piers and historic structures in the town. The façade along Haigh Terrace is composed of red brick set within bands of stone, again similar to Victorian buildings in the town including the Carnegie Library. Flat areas of the roof are planted as green roofs, increasing the visual amenity of the building. The existing pond had to be removed and rebuilt close to its original location.

The brief for the building was to construct a Central Library and Cultural Centre comprising a children’s and teenagers’ library, a reference library, modern IT facilities, art gallery (with a workshop area next door), an auditorium, coffee shop and cultural centre and meeting rooms. It has a car park with 100 spaces, as agreed with the planning department. The close proximity to major public transport routes has been factored in to the required number of parking spaces. The building will also serve as library headquarters for the county.

The project was an exciting one from the start. Moran Park is on two levels, 15m above Ordnance Survey Datum along the Haigh Terrace boundary and 9m above Ordnance Survey Datum on the Queens Road (The Metals) boundary. It is approximately 1.17 hectares and slopes downwards from southwest to northwest. It provides a connection between the town centre and the sea. The site consists of a flat portion and a portion of steeply-sloped, rocky incline running parallel to Haigh Terrace. The site width varies from 18m at the north end of the site to 35m at the south end. The site is close neighbours with the Royal Marine Hotel, the National Maritime Museum, the DART and Moran Park House.

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The site prior to construction

The site was an old quarry, an area of which subsequently became a reservoir providing fresh water to the ships that came to Dún Laoghaire harbour. Finally, there was a bowling green and clubhouse, which were relocated to a new site, with new facilities in Eglington Road, Dún Laoghaire. The tender price of €27,450,000 excluding VAT was accepted and construction commenced in April 2012. At its peak, there were 160 people working on site, not including supervisory staff.

Engineering challenges


The first major challenge was to remove the granite rock and create an even level on which to commence the building. The removal was sub contracted to CMT Rock Services Ltd. The rock was extremely hard, and plant such as excavators and hammers alone would not be able to remove it.

CMT drilled hydroexpansive chemicals into the rock. The chemicals expanded and, after a number of hours, cracked it. The excavators and breakers then broke out the rock. The ‘breaking out’ took over six months and it is fair to say that our neighbours were not best pleased! In total, approximately 13,500m3 of rock was removed from site. As the rock was being removed, the embankment supporting Haigh Terrace and the Royal Marine Hotel had to be reinforced. For this, shotcrete was sprayed on the embankment and soil nails were fired into it. All was going well until there was a major safety incident.

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Rock being broken out on site

Overnight, there was a partial collapse of the embankment. Nobody was injured and access to Haigh Terrace was quickly closed off. It transpired that one of the soil nails had hit a post of the boundary fence and had not penetrated the embankment fully. Next, the green sludge that was the existing pond was pumped into a holding reservoir to try to dry it out. Very little dried out, however, so it was then covered with lime to solidify it and it was removed off site to an approved landfill site.

The Building – Construction Issues


The building itself is a concrete frame clad with granite and brick. It is spread over four floors, with a total area of 6,520m2. The foundations were relatively straightforward due to the building being founded on granite. There was an existing 2.1m foul sewer about 8m below the foundations. However, due to its depth, there were very few structural implications. Horgan Lynch entered into early negations with Iarnrod Éireann, which insisted on vibration monitoring of the DART line. The Maritime Museum is a protected structure that also required vibration monitoring. The vibration limits on any area of the site were never exceeded. A series of chimneys form a spine down the building and contribute to its overall stability. The chimneys bring air down into the building from the wind cowls on the roof.

The building is held together by thirteen V-beams at roof level. During design stage, the temporary stability of the building during construction was considered. One of the hardest working elements in the building were the long spanning walls. These were very heavily reinforced and were propped until their design strength was achieved. Thirteen V-beams tie the building together at roof level. These beams, so named due to their shape, were constructed by Banagher’s in Co Offaly. The beams weigh approximately 40T each. John Sisk had to apply for an abnormal load licence from the traffic department of DLRCC.

The beams were then brought to site in the middle of the night (one per night) and erected the next day. Two 350T cranes were used in a tandem lift to position the beams into place. The task was further complicated by the wind gusts off the harbour and also one landing wall was straight and the other one was at an angle. Finally, the design of the beams meant that the weight of each beam was not central and they had a tendency to tip forward.

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Collapse of the temporary embankment support at Haigh Terrace

The finish inside the building is an exposed in situ concrete finish. The concrete is a blend of 50% ordinary Portland cement and 50% ground granulated blast furnace slag, which ultimately gives the concrete a very white appearance. There were strict limits on blowholes, lipping from the shutters, discolouration, grout loss and honeycombing. To learn more about perfecting such a finish, the site team made a visit to a site in Birmingham where a similar finish was employed. The client also employed a concrete expert, David Bennett, who guided the team through the production process and through any necessary repairs.

The stone cladding for the building was sourced in Spain. The specification for the stone was very tight, with rigorous limits on colour, markings and inclusions. The outside of the building is clad with a rubber membrane (ethylene propylene diene monomer), then covered with 160mm of insulation. There is an 80mm air gap and then the stone cladding is fitted. All this keeps the heat in the building.

Heating is provided through trench heaters, underfloor heating and a very few small radiators. There is sound proofing under the floors and in acoustic panels strategically placed on the walls. The extensive hardwood timber panelling contribute to the noise reduction. This is all very important when a rock band is practising under the library reading rooms!

Energy and Ventilation


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V beams being fitted with hardwood cladding

Primary energy for the building is provided from renewable sources, where possible. The heating of the building will be from both gas-fired and biomass fired boilers. DLRCC has an ample supply of wood chips generated by the extensive parks in the county. The wood burning boiler has a very high heat efficiency with a short payback period and provides green energy to the building.

Nine wind cowls provide ventilation from a passive system that uses the wind and the stack effect to provide fresh air and extract stale air to and from every room in the building. It also provides for heat recovery and has been developed to harness natural wind currents to create air pressure sufficient to provide of a plentiful and healthy fresh air supply with no energy cost. The system also uses passive stack ventilation principles. It can operate in near-windless conditions, although the main period of its use is in winter, when there is normally more wind. The aspiration system draws air continuously into a smoke-sensitive chamber. In the event of fire, a message is sent to the fire alarm for very early fire detection.

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Wind cowls in place on the roof of the Lexicon

Moran again

Moran Park pond – after reconstruction

In keeping with the cultural theme of the building and in accordance with guidance from the Department of Arts, Heritage and the Gaeltacht under the ‘Per Cent for Art’ scheme, a budget was set aside to procure a piece of public art. Seventy-plus entries were received and the winning artist was Katherine Lambe. Her stunning design comprises coloured backlit glasswork, which represents Dún Laoghaire’s ‘mountains-to-sea’ environment.

In addition, the bronze ‘Christ the King’ sculpture which was originally on another part of the site, has been cleaned, relocated and now presides over the car-park entrance.The outside space is dominated by the pond that has been reconfigured in its existing location and relates to parking below. There is a central island, which is planted with bamboo and provides ventilation for the car park.

The pond features weirs and concept lighting, and the water that will be pumped around the pond will be reused and filtered using a UV filtration system. There is a connection to the Royal Marine garden green space, with plenty of seating areas. The Central Library is a stunning building and a credit to DLRCC, the architects and John Sisk & Son. The views from inside the building are particularly noteworthy. It will be a huge asset both to Dún Laoghaire and the greater Dublin area.

Marcella

Author: Marcella Murphy, senior executive engineer, Dún Laoghaire-Rathdown County Council. After graduating from UCD, Marcella Murphy worked with Lancashire County Council for six years, where she was trained in the design and construction of bridges and became a chartered engineer (MICE). When she returned to Ireland, she worked in the private sector, carrying out the design of bridge structures. Murphy then moved onto the M50 to supervise the construction of bridges with Dun Laoghaire-Rathdown County Council. During this time, she did an MBA with the Open University. She then joined Jacobs Babtie for two years before returning to Dun Laoghaire-Rathdown. She is a senior executive engineer, although she spends most of her time as a senior resident engineer. 

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The Central Library represents the biggest single investment by Dún Laoghaire-Rathdown County Council in a civic amenity. Under the 2004-2010 Dún Laoghaire-Rathdown (DLR) County Development Plan, the Central Library was envisaged as a crucial element of a programme of regeneration. The councillors agreed to proceed to an architectural competition...