The new €42m EPDC/5 facility consists of 11,488 square meters of floor area together with 322 car-parking spaces.

The building, designed by Gilligan Architects, comprises a three-storey facility over basement car parking. Car parking is also provided at ground level on a podium structure. The floor plates are generally 50m x 50m with a 22.5m x 22.5m central atrium area. Four no. stair/lift cores provide circulation. The basement car parking is generally class 1 category with class 4 category local to 3 number stair/lift core areas serving the basement. This basement area extends beyond the building footprint under the podium level service road and car parking areas and required a total excavation volume of 40,000 cubic meters of which 22,000 cubic meters was Granite rock.

A curved and inclined three-storey glazed wall provides the external focal point at the main entrance that leads into a 510 square meter atrium space covered entirely with roof glazing. Aluminium framed glazing/cladding covers the major area of external elevations and the remaining core elevations are finished in limestone cladding.

The building was initially planned as a development/investment opportunity with fixed lease agreements to Microsoft. However due to marketplace conditions, Microsoft negotiated a contract with building contractors, G & T Crampton Ltd.

Various structural schemes were proposed including a concrete flat slab structure. However, based on programming requirements, the chosen scheme was a steel framed three-storey building set out on a 7.5m x 7.5m grid layout. UC sections were used for column and the floor structures comprised a 335mm deep composite concrete slab on SD 225 decking which in turn is supported on ASB beam sections. To accommodate the higher loading of the ground floor to the atrium a 300mm deep flat slab structure was provided. A flat slab structure on concrete columns provides for the podium areas and all core walls are formed with insitu concrete.

Microsoft EPDC/5

Initially it was intended to provide expansion joints through the building but on review of core locations, it was decided to engineer out building movements utilising the 4 no. perimeter cores and by providing UC steel tie beam sections between columns at floor plate levels. A total of 700 tonnes of hot rolled steel sections together with 40,000 cubic meters of concrete make up the structural frame.

Lateral stability is achieved via floor plate action through to the 4 no. concrete core structures. Steel members supporting the glass atrium roof and inclined/covered glazed entrance facade comprises CHS sections of various dimensions connected by steel side plates to form unique tapered elliptical profiles.

Substantial geotechnical investigations were initiated at early stages to establish rock contour levels. In general, granite rock was found to underlie approximately 600mm of topsoil/gravely clay. As a result, conventional pad/strip footings were used as foundations. These were designed to be integral with the basement concrete slab.

In September 2001 G & T Crampton Ltd commenced on a 19-month construction programme broken into two stages i.e. (1) Shell & Core (2) Fitout. In July 2003, Microsoft Ireland gained possession of its new EPDC/5 facility on time and on budget.

Joe Ryan,
Hanley Pepper

Recent projects undertaken, with interesting structural aspects, include the construction of an aircraft hangar (in excess of 60 metre clear spans) in Casement Aerodrome to house the government jet and fishery protection aircraft, major upgrading of the runways in Casement Aerodrome, the refurbishment of the main wharf and the provision of fuel storage facilities in the Naval Base in Haulbowline.

Also the construction of a number of specialised ammunition and explosive storage buildings has been recently completed. These are very heavily reinforced concrete bunkers, semi buried, designed to eliminate the danger of sympathetic detonation between bunkers.

The Corps of Engineers is also responsible for engineering works associated with Defence Forces operations overseas, i.e. provision of accommodation, shelters, services, road upgrades if required etc. Works undertaken in the last year include the construction of RC foundations and floors for workshops and accommodation facilities in very poor ground conditions in Liberia, and the upgrading of living accommodation and office facilities for Irish troops in Kosovo.
Jim Foley, Lieutenant Colonel, Contracts Officer, Corps of Engineers

As designers, we should take advantage of the transition period to get our Eurocode knowledge up to the same level as our current knowledge of the extant practices. The transition period will be surprisingly short when the withdrawal of the current codes will herald the end of the dual operation and the beginning of the full application of the Eurocodes.

There are nine main euro codes or euro norms covering the methods of design and use of the main materials in structural engineering: -

• EN 1990 Eurocode: Basis of structural design
• EN 1991 Eurocode 1: Actions on structures
• EN 1992 Eurocode 2: Design of concrete structures
• EN 1993 Eurocode 3: Design of steel structures
• EN 1994 Eurocode 4: Design of composite steel and concrete structures
• EN 1995 Eurocode 5: Design of timber structures
• EN 1996 Eurocode 6: Design of masonry structures
• EN 1997 Eurocode 7: Geotechnical design
• EN 1998 Eurocode 8: Design of structures for earthquake resistance
• EN 1999 Eurocode 9: Design of aluminium structures

A designer will have to make reference to several of these codes to gather the rules for a particular structure because the philosophy of the arrangement of the text is to eliminate duplication; each code only carries rules for the specific area of design featured in the title and makes reference back the other codes such as EN 1990 where basic rules are defined. For instance, EN 1994 refers the designer to EN 1993 for steel and EN 1992 for concrete rules. Composite action is not covered in EN 1992 or EN 1993 except by reference to EN 1994.

Each code has been sub divided into parts and sections with greater detail for particular aspects of design in the scope of the code. For example, the material codes 2 to 6 and 9 each have a part covering fire resistance for those materials, but each in turn refers back to EN 1991, which covers the basic aspects of the actions of fire on structures as well as the permanent, transient and variable loads that are used for all materials.

New words and terminology have been adopted in the text that are scientifically and grammatically correct, without ambiguity in each of the three main languages, English, French and German, of the European community.

This is a significant harmonisation of engineering knowledge, incorporating as it does the very latest proven technology for the structural designer. Whilst general agreement has been reached on the vast majority of factors and characteristic values to be used with the rules of design, some variation between nations has been permitted to account for regional variations in climate and working practices. These variations are held in the National Application Document for each code; any design for a specific country must be made using not only the rules in the relevant Euro norm but using also the variations permitted in the appropriate National Application Document. A French designer of a structure to be erected in Ireland may use the Eurocode published by the French Standards Authority (AFNOR) but the designer must use the variations required by the appropriate National Application Document for Ireland published by the National Standards Authority of Ireland (NSAI).

You may already have noted that many supporting standards for the production, testing and installation of products have recently been published, these are required ahead of the design rules to ensure that these supporting standards are in place before the design rules are implemented in each of the European Countries.

Like the Euro, the introduction of the design Euro Norms will be sensibly almost on the same day; they must be published within six months of the date of availability.

Colin Short,
Colin Short Associates

The study, which is published in June 2004, is based on Q4 2003 prices, but the favourable competitive situation which it reveals is largely unchanged by the recent steel price rises. The report was prepared with input from Ove Arup & Partners, MACE, Davis Langdon and the Steel Construction Institute. It is the latest in a series of steel versus concrete cost comparison studies for offices that goes back to 1993. The original 1993 study considered several different steel and concrete based framing options for a four storey, 2600m2 developers specification building, and an eight storey, 18000m2 prestige office building. The detailed specification, particularly for services, and locations, have been modified over time to reflect the evolution of client requirements.

All of the steel schemes considered are faster and more cost effective than all the concrete alternatives. In 1995, the typical cost advantage for steel was around 10%; by the end of 2003 this had widened to 32%. Considering inflation and using department of trade and industry cost indices reveals that the cost of the steel schemes has reduced by 14% in real terms. Over the same period the real cost of the concrete options has increased by 16%.

Majella Smith,
Corus

Benefits are obtained from the difference between a general approach and a more thorough individual approach. The general approach for safety evaluation of existing bridges is based on codes and regulations for evaluation of bridges. The fact that codes generalise to be applicable for the design of many types of new bridges is efficient because the load and safety calculations become easy and because the extra cost due to the generalisation is marginal in the budget for a new bridge.

Skovdiget West Bridge

But in the case of rehabilitation or strengthening of an existing bridge, the required safety or load carrying capacity can often not be obtained from the general approach and the result may be an expensive strengthening or replacement project.

The individual approach is based on the concept that a bridge does not necessarily have to fulfil the specific requirements of a general code, as long as the overall level of safety defined by the code is satisfied. In other words the purpose of the individual approach is to cut or reduce the strengthening or rehabilitation cost without compromising on the level of safety. In this method, safety evaluations are based on probabilistic methods. In a probabilistic-based safety evaluation the uncertainties of the specific bridge condition and the local traffic situation can be taken into account consistently. It could be said that this approach establishes a ‘code’ for the individual bridge.

Examples are presented where the application of a probabilistic-based assessment approach has resulted in savings of over €30 million.

Skovdiget West Bridge (Saving ~€20 million)

Skovdiget West BridgeThe Skovdiget identical twin bridges were constructed in 1965-67. The bridges are concrete post-tensioned, combined box-girder and beam-slab bridges. Due to poor workmanship and poor design, both bridges started to deteriorate shortly after construction. The damage was related to un-injected or poorly injected post-tensioned cable ducts, insufficient drainage, bad waterproofing and an uneven bridge deck.

A major repair was performed on the East Bridge in 1978. The repair proved so costly that is was decided to leave the West Bridge without repair. Instead it was decided to monitor the West Bridge closely.

In 1998 RAMBØLL performed a probabilistic based assessment of the structure to optimise maintenance and provide a management strategy for the structure. By use of a probabilistic-based assessment model and stochastic modelling of load (including traffic) and resistance (incorporating a stochastic deterioration model) the safety of the structure was established. Using estimates of future deterioration the remaining service lifetime was found to be 7-8 years. This was extended to 15 years by implementation of a cost optimal plan without compromising the level of safety prescribed by the code. The overall result is a saving of more than €20 million when compared to the result of a traditional deterministic analysis, i.e. immediate replacement of the structure.

Probabilistic and Plasticity Based Assessment of a Concrete Slab Bridge (Saving ~€1 million)

Plastic response analysis and probabilistic-based safety analysis are combined using RAMBØLL’s program PROCON. The intention is to use models, which are closer to the actual structural behaviour in the failure situation and to the safety of the bridge.

The bridge considered is from 1942 and was constructed to under-pass a 4-lane motorway for a small factory railroad with a span of 4.43 m, a width of 24 m and a skew angle of 25.6°.

Motorway bridges in Denmark are required to have a minimum capacity termed Class 100. This requires the structure to be capable of supporting side-by-side a 100t and a 50t truck positioned at the critical location. The result of an elastic FE analysis is that only 29 % of the load from the class 100 truck can be carried together with the dead load and the class 50 truck.

The analysis with PROCON is that 79% of the load from the class 100 truck can be carried.

The result of the probabilistic-based safety analysis is that 116 % of the load from the class 100 truck can be carried. The use of plastic analysis in combination with probabilistic analysis makes a strengthening project redundant with considerable cost savings.

Examples of the savings made on various projects are indicated in Tables 1 and 2.

Table 1: Comparison of Deterministic vs. Probabilistic Assessment of 4 Danish Bridges

Table 2: Comparison of Load Carrying Capacity from Deterministic vs. Probabilistic Assessment of 3 Swedish Bridges

The general approach for assessment of existing bridges by application of standard general codes is quick and efficient, but can be costly due to expensive strengthening or rehabilitation projects. The individual approach incorporating probabilistic-methods is based on the concept that a bridge does not necessarily have to fulfil the specific requirements of a general code, as long as the overall level of safety defined by that code is satisfied. The individual approach is therefore able to cut or reduce the strengthening or rehabilitation cost without compromising on the level of safety.

In Ireland as Eirspan moves to the next phase in 2004, i.e. structural assessment, it is likely that a percentage of the Irish national bridge stock will be deemed ‘unsafe’ by traditional deterministic analysis. It is therefore important that engineers embrace advanced methods so as to avoid costly and unnecessary bridge strengthening or replacement.

A lecture entitled Cost Savings in Bridge Assessment by Application of Advanced Methods will be presented by the authors at 7pm on Tuesday 18th November 2003 in The Ussher Theatre, Arts Block, Trinity College Dublin.

Dr. Ib Enevoldsen (ibe@ramboll.dk)
Dr. Alan O’Connor (alo@ramboll.dk)
RAMBØLL Consulting Engineers (www.ramboll.dk), Denmark

Smithfield Market Development

White Young Green are acting as the Civil & Structural Engineering Consultants to the Client, Fusano Properties Ltd. G & T Crampton are the Main Contractors and Horan Keogan Ryan Project are Architects on the development.

It was clear from an early stage that a water table cut-off-wall would be required to dewater the site and facilitate construction of the 3 storey-deep basement structure.

Various alternative forms of construction were considered for the cut off wall and it was decided to proceed with a solution involving an 800mm thick diaphragm wall around the perimeter of the site and the less expensive slurry wall construction was utilised for internal walls to permit the site to be developed in 3 areas concurrently. The perimeter diaphragm wall involved 400 linear meters with depths varying from 15-20m below adjoining street level.

The water in the limestone rock fissures in Smithfield was found to be under artesian pressure and there was a risk that vertical water flows could present difficulties in the dewatering regime. Prior to the works being carried out rock cores were drilled to investigate the rock fissures below the site and a unique pump test was carried out which was designed to ‘mimic’ the water flow conditions below the wall. The actual flow rates currently being recorded under the completed wall agree favourably with the predicted flows as per the trial pump test.

Smithfield Market Development

Cementation Skanska were employed to carry out the specialist design and construction of the diaphragm wall. They also constructed the temporary diaphragm wall anchors that prop the wall excavation, and the uplift anchors to prevent floatation in the permanent works.

The building superstructures generally consist of reinforced concrete flat slab construction throughout the entire development with some areas framed with structural steelwork and composite decking.

The building heights generally consist of 13 storeys in total inclusive of 3 basement level storeys below ground. The lowest basement level is some 11m below the adjoining street level. As part of the central phase both the structural design and foundation sub-structure includes for the provision of a 20-storey high tower structure.

White Young Green services on the development are being provided from the Dublin and Belfast Engineering and Environmental Offices. The Smithfield Markets project commenced on site in August 2002 with the final phase due to be handed over to the Client circa summer 2005.

Paul Halpin, (paul.halpin@wyg.com)
White Young Green

Underlying ground conditions at the site consist of karstic limestone typically exhibiting fissures and voids.  All elements of the sub-structures excluding the anchorage abutment are supported on bored piles, 1500mm diameter for the pylon and 900mm for all other piled substructures.

The pylon is an inverted ‘Y’ in elevation.  The rectangular legs are hollow allowing full access internally to the pylon head for personnel and equipment.  This allows stays to be stressed from inside the pylon head. The south (anchorage) abutment is a multicellular reinforced concrete box partially filled with concrete, with a total weight of 17,000 tonnes and provides the anchorage to the back stays of the pylon.  Permanent access to this abutment is provided so that stays can be stressed and anchorages inspected.

The bridge deck on all spans consists of 230mm concrete slab acting compositely with a structural steel ladder beam.  The latter consists of a pair of longitudinal steel girders 1750mm deep minimum with steel cross girders at 3.333mm centres. The cable stays which are at 10m centres on the main span are connected to cross girder extensions.  All of the structural steel is enveloped by a pultruded GRP enclosure so that conditions close to indoor conditions prevail within the enclosure.  The steel is left unpainted and it is expected that in these conditions the steel will require very low or possibly no maintenance in the future.  The enclosure provides a ready-made access platform for the future inspection of the steelwork, deck soffit and movement joints.  The main span of the deck is supported by an inclined plane of stay cables at each side of the deck.  The fourteen stays on each side fan out in a semi-harp arrangement from the top of the pylon, providing reasonable space for stressing purposes whilst maintaining the advantage of steeper inner stays.  The stays were installed using the Freysinnet iso-tension system of strand by strand installation where each individual strand in a stay is stressed using a monostrand jack.

Specialist studies carried out at the Preliminary Design Stage indicated that wind susceptible vehicles had a considerably higher risk of overturning on the bridge than on the motorway approaches.  In addition these studies established at the provision of 2.1m high windshields with 45% porosity at the edges of the bridge would reduce this risk to a level comparable to the risk along significant lengths of the Northern Motorway both existing and proposed.  The wind shielding consists of three transparent polycarbonate panels each 370mm wide with 380mm clear gaps.  The panels are supported by aluminium posts at 2.5 centres.  This arrangement allows for reasonably uninterrupted views along the Boyne Valley.

The aerodynamic response of the deck and windshields was assessed by carrying out wind tests on a sectional model in a wind tunnel.  Analysis of the results indicated a satisfactory deck response.  The measure of force coefficients were used in the detailed design of the deck while static pressure distribution measurements around the deck section were used to obtain local design wind pressures to be used on the design of the enclosure system.

The efficiency of the windshields was determined by measuring the side force and overturning moment on a model of a furniture van positioned on the deck.  Measurements were taken with and without windshields.  Analysis of the results confirmed the findings of the original wind shielding study.

Architectural lighting of the bridge gave the opportunity to highlight and reveal the bridge from a number of standpoints.  A line of side emitting fibre optics in white, located below the edge beam of the deck produces a fine sharp line to delineate the deck and frame the white roadway lighting.  Narrow beam luminaires mounted on the deck and anchorage abutment and directed up the cables pick out the stays in a deep blue colour.  As the beams converge towards the pylon heads they have the effect of strongly highlighting the bridge structure.  Light projected up the outside of the pylon from locations at the base helps to define the pylon shape.  The inside faces are lit in a similar manner providing a dramatic arch for motorists to drive through.  Finally, the recess at the top between the pylon legs is brightly lit to ensure a measure of drama.

The inclined legs of the pylon were constructed in 6m high pours using the lightweight Alumna falsework system similar to that used on the Charles River Bridge in Boston, USA.  In this system the formwork is supported from a truss, which is constructed between the legs and is initially supported from the ground.  As the legs rise upwards, members of the truss are removed from the bottom and reassembled at the top of the falsework.  In this way the falsework ‘climbs’ with the legs and is supported from the legs.  The falsework also serves to keep the legs in their correct lateral positions, obviating the need for jacking the legs apart prior to constructing the pylon head.

For the pylon head, the contractor adopted 3m high pours with the steel plates of the stem liners forming the inner faces and the RMD system of climbing formwork for the outer faces.

For the four spans on the northern approaches to the bridge, the contractor welded the longitudinal steel beams on the ground and lifted them into position on the approach span piers.  The cross girders were then bolted to the longitudinal girders.  ‘Onmia’ planks were placed on the steel framework and the insitu concrete slab was poured starting at the north abutment.

While the approach spans were being constructed, the steelwork for the main and back span were assembled on stillages behind the south (anchorage) abutment, along the lines of the motorway.  The outer permanent back stay (B14) was installed and used to stabilise the pylon during the launch.  The steelwork was transferred to two computer-controlled multi-axle trailers and a skate located at the rear of the anchorage abutment.  A temporary post and stays (T1 and T2) were installed to support the leading cantilever until it reached the pylon.  A hauling line was anchored behind the north abutment and connected to the leading end of the steelwork.  The steelwork was launched by driving the trailers forward and pulling on the hauling line.  The trailers also provided braking to control the launch.

When the steelwork had reached the pylon, the temporary post was removed, the skate moved to the back of the abutment and temporary stay T1 connected to the top of the pylon.  The launch then continued with the following cycle:

• pull,

• adjust length of temporary stay,

• survey, and

• move skate back.

As temporary stay T2 passed the pylon it was also connected to the top of the pylon and the launch continued with two temporary stays.

When the steel girders were in the correct longitudinal position, they were lowered to their final levels at the anchorage abutment and pylon and the level adjusted at the closure joint.  The steel girders were then welded to anchorage plates in the south abutment and to the end cantilever of the approach spans.

The concrete deck was constructed starting at the pylon and working firstly towards the anchorage abutment and then northwards across the main span.  As the slab reached the position of the first fore stay (M1), the first permanent back stay (B1) was installed followed by the first permanent fore stay M1. The next 10m of slab was poured and stays B2 and M2 installed.  Construction continued with a typical cycle:

·         pour 20m of slab,

·         install two pairs of back stays, and

·         install two pairs of fore stays.

As the construction face reached the temporary stays T2 and T1, they were removed followed by the hauling cable.  Finally, the precast edge beams and deck furniture were aligned and fixed in position, the GRP enclosure installed and the roadway surfacing laid.

The piling works were carried out by Ascon Ltd. as an advance contract.  The bridge with approximately 500m of motorway was constructed by SIAC – Cleveland Bridge J.V.  The bridgeworks are due to finish in early Summer 2003 and will have taken three years to construct.  The total cost of the bridge was €35.8 million excluding V.A.T.

Joe O’Donovan, Roughan O’Donovan

IEI Paper – The Design and Construction of the Boyne Bridge (1.20MB)

Architects and engineers prepared approximately 1,300 comprehensive blueprints to guide the project, which was on the “drawing board” for three years, from conception to completion.  Challenging and often brutal weather conditions made it extra taxing for construction crews on Top Thrill Dragster with hurricane force winds (up to 75 mph); significant snowfall (a total of 60 inches); and frigid temperatures (a wind chill of -30 degrees) on the shores of Lake Erie. One hundred and fifty-one bright yellow steel support columns were carefully positioned and make up Top Thrill Dragster’s looming structure. Ninety-four individual pieces of red and white steel track were pieced together to create the portion of the coaster where its trains will race at speeds reaching 120 mph. Top Thrill Dragster’s enormous structure is anchored by 149 footers, which required more than 9,000 cubic yards of concrete.

A construction crew of roughly 200 workers has been assigned to varied tasks on Top Thrill Dragster such as pouring foundations and erecting steel to electrical engineering and building the coaster’s station. Six sleek “dragster-style” trains – weighing 5 tons each – will be assembled and installed on Top Thrill Dragster’s 1,150-ton structure. One hundred five miles of electrical cable – or enough to travel from Cedar Point to Detroit is being installed for the complex electrical engineering of Top Thrill Dragster. The construction process of Top Thrill Dragster required 5,400 bolts. Five cranes, including two that stretched an incredible 480 feet in the air, helped position Top Thrill Dragster’s track and structure into place. The 480-foot-tall cranes were two of only four in the United States that could accommodate a project of the towering 420-foot height of Top Thrill Dragster. Approximately 90 truckloads of steel were shipped by boats and eventually trains and trucks – from Europe to Cedar Point, where the coaster parts were stored in a massive parking lot and later assembled at the job site.

The first opportunity for guests to “Race for the Sky” on Top Thrill Dragster is on Cedar Point’s Opening Day, Sunday, May 4. Until then, roller-coaster-riders can log on to cedarpoint.com for frequent updates and top thrills.

The approaches used at the moment vary considerably and it is questionable if this approach is yet sufficiently well established to be used for general bridge assessment. However, there is some degree of convergence in European thinking as can be seen from the COST 345 action, “Procedures for the Assessment of Highway Structures”, the final report of which is due out this year.

Research to improve our understanding of traffic loading is ongoing at UCD. For example, the Eurocode allowance for dynamic impact is quite conservative – it is based on tests carried out in Switzerland of single trucks crossing bridges. It is known that dynamic excitation occurs when the frequency of the truck crossing speed coincides with the natural frequency of the bridge. However, the vast majority of bridges have two or more lanes and the critical loading event consists of two or more trucks meeting (or passing) on the bridge.

The dynamics of a two-truck loading event is not easy to predict – it is affected by the relative speeds and the point at which the trucks meet. However, you can reasonably expect interference in the dynamic excitation effect of each truck which would give a much reduced dynamic amplification overall. This is being modelled at UCD at the moment and tested in the field through a collaboration with the Slovenian National Building and Civil Engineering Institute. The results may form the basis for a future revision to the Eurocode traffic load model.

So, what will happen in the future? One idea that is being investigated through a European research project is a bridge that communicates with the truck so as to guarantee that dynamic excitation does not occur when two trucks meet on it. The bridge will detect the approaching trucks and, if their speeds and calculated meeting point are such as to cause a problem, the bridge will instruct one or both of them to slow down. It may sound far fetched but this is the kind of thinking being used to try to get the maximum out of the infrastructure that we already have and to minimise the need to strengthen or replace bridges using non-renewable materials.

Eugene OBrien
Civil Engineering Department, UCD

The William Dargan Bridge, Dundrum

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