Cian O'Donnchadha gave a presentation on the structural development of the Wexford Opera House project. He discussed choosing precast concrete voided slabs and beams due to advantages like quality finishes, shallower construction, and faster installation. Site photos from August 2009 to March 2010 showed excavation, piling, and the concrete structure taking shape despite weather challenges. Fairfaced concrete was used to achieve a high quality soffit finish.

1. Presenter
Cian O’Donnchadha BEng CEng MIEI MIStrutE
4th Year Civil Engineering Arup Consulting Engineers
5th March 2009
NUIG School of Engineering
Wexford Opera House

2. Presentation Overview
• Structural Development
• Precast Concrete – Voided Slab
• Precast Concrete – Beams and Double T Units
• Site Progress – August 2009 to November 2009
• Fairfaced Concrete
• Site Progress – Weather
• Site Progress – Dec 2009 to March 2010
NUIG School of Engineering
Wexford Opera House

3. Structural Development
NUIG School of Engineering
Wexford Opera House

4. KEY STRUCTURAL CHOICE CRITERIA
Architectural Issues at scheme stage– Grid
• An initial planning grid of 1.5 m
• A west wing width of 18.0 m and an east wing width of 11.0 metres.
• A grid spacing along the building edge of 7.5 m
• A notional building height of 4 storeys was assumed at concept stage.
• Central Bay 30m long
West Wing – Structural Grids
4.5m Span + 9.0m Span + 4.5m Span 2 No 9.0m Spans
3 No 6.0m Spans
NUIG School of Engineering
Wexford Opera House

5. Other Factors Influencing Structural Choice
In addition to the usual issues of cost and programme we have also considered issues such as adaptability,
flexibility, partition systems, weights (foundation loads) etc.
Site Disruption:
•Amount of traffic into and out of site.
•Nuisance caused by construction process (Noise, Vibration, Dust etc)
•Equipment associated with the construction process.
•Neighbour issues
Adaptability:
•Capacity for future service penetrations (both vertical and horizontal).
•Ease of insertion or removal of stairs, lifts, floors.
•Response to changes in loading requirements or capacity for late Client Changes.
Services:
•Ease of services integration. Flat soffits or limited steel beam depths are ideal. Can primary and secondary
service runs follow beam/downstand layouts?
•Are there problems associated with vertical ductwork.
•Ease of addition of future services
Procurement:
•Lead in times and any effect on design programme/design freeze.
NUIG School of Engineering
Wexford Opera House

6. Buildability:
•Achievement of good tolerances/good fit.
•Sensitivity to weather conditions.
•Lack of reliance on temporary works and following work (cleanliness)
Cladding:
•Ease of base and head fixings. Stiffness and stability provided by base structure.
Soffit Quality:
•This covers soffit treatment. Solutions such as precast slabs may require only painting, steel frames may require
suspended ceilings. This will also have an effect on thermal issues.
Partitions:
•Ease of base and head fixings, flat soffit allows for easier and quicker installation.
•Does the structural grid tie in with planning grid?
Thermal:
•Effect of structure mass on diurnal temperature fluctuations within building.
•Ability to cool and heat a structure out of hours (night time cooling).
•Ribbed soffits have more exposed area and are more efficient than flat soffits
NUIG School of Engineering
Wexford Opera House

7. Depth:
•Influence of slab depth on services and building envelope.
Sound/Acoustics:
•Influence of structure mass and soffit on sound/acoustic characteristics
Speed:
•Influence of structural system on construction programme.
•Early weather tightness and optimisation of following trades.
Stability:
•Lateral stability, ease of provision and effect on programme.
•Construction of insitu concrete core walls may be on critical path.
Foundations:
•Influence on total building weight and thus on foundations. Limitations on pile numbers and rate of piling.
Cost:
•Overall cost (including effects of time). Fast construction may have higher cost for construction. Shorter overall construction
programme may give lower total cost if cost of money is allowed for.
NUIG School of Engineering
Wexford Opera House

8. Scheme workshop with RMJM architects
NUIG School of Engineering
Wexford Opera House

9. Models of different Structural Solutions
NUIG School of Engineering
Wexford Opera House

10. Choice of Material
Insitu Concrete Construction
Advantages Disadvantages
•Increased thermal mass, particularly with ribbed •An exposed concrete soffit can be expensive when
forms of construction. producing a high quality finish. (Costs may be offset
against suspended ceiling costs).
•With flat slab construction, detailing of partitioning •With the use of post tensioned concrete a limited
systems is simple number of contractors are available (2-3).
•On a 7.5 m grid, good cladding support with •A heavier form of construction (compared to steel),
minimal deflection. which can result in an increase in foundation costs.
•On long span particularly post tensioned, vibration •In general with insitu construction there is more
and deflection can be more easily controlled disruption to the site due to the construction process
compared to steel (Concrete deliveries etc)
•Easier to accommodate changes to elements/details •Longer site period compared to steel.
at a later stage
•Shallower form of construction compared to steel.
•Short lead in, 6 – 8 weeks
NUIG School of Engineering
Wexford Opera House

11. Choice of Material
Precast Concrete Construction
Advantages Disadvantages
•Prestressed units control deflection, vibration and
•Not ideally suited to a 2 way spanning system.
cracking.
•High quality finish can be part of a factory-produced •Lead in times are comparable with steel (12 – 14
product. weeks).
•Exposed concrete aids thermal mass particularly if •Joints/details need careful attention and early
ribbed. resolution.
•If a high quality frame is required, only 2 –3
•Good for one-way spanning systems.
contractors can supply a satisfactory product.
NUIG School of Engineering
Wexford Opera House

12. Choice of Material
Steel Frame Construction
Advantages Disadvantages
•Speed on site. •Long span options tend to experience vibrations and
deflection problems.
•Procurement – good range of locally available •Unless structure and slab is exposed (with the
subcontractors resulting industrial type finish), little thermal mass
advantages are gained.
•Minimal site disruption. •With the fabrication drawing and manufacture
programme, an earlier design freeze is required.
•Lightest form of construction generally. •Late alterations are more difficult to accommodate.
•Cladding support may cause problems on long
spans.
•A deeper form of construction, in many cases adding
to the overall building height as compared to other
alternatives.
•Lead in of 12-14 weeks required (from drawings to
steel on site).
NUIG School of Engineering
Wexford Opera House

13. Options for the West and East Wing
The West Wing
8 structural options have been developed on the basis of the 2 structural grids as highlighted
•Grid Type A 14.0m span
•Grid Type B 2No. x 7.75m spans
NUIG School of Engineering
Wexford Opera House

14. The following 8 options were investigated in the West Wing
Option 1: Voided Flat Slab (Grid Type A).
Option 2: Composite Concrete Wide Slab onto Cellular Beams (Grid Type A).
Option 3: Post-Tensioned Concrete Rib Slab (Grid Type A).
Option 4: Hollowcore Precast Floor and Steel Beams (Grid Type A).
Option 5: Voided Concrete Flat Slab (Grid Type B).
Option 6: Composite Concrete Wide Slab onto Steel Beams (Grid Type B).
Option 7: Steel Metal Deck (Grid Type B).
Option 8: In-Situ Flat Slab (Grid Type B).
NUIG School of Engineering
Wexford Opera House

15. Option 1: Voided Flat Slab (Grid Type A).
Advantages for a two-way precast soffit system Disadvantages
(Voided Slab) reinforced
•High quality, steel mould finish ready to paint. •Long lead in 12-14 weeks.
•Shallower form of construction compared to •Expensive.
traditional insitu concrete.
•Good fire resistance / Acoustics •Limited specialist Sub-contractor (2).
•Good thermally. •Not previously used in UK or Ireland (European).
•Good for partition head/base fixings. •Openings restricted to central areas.
•Slim and lighter form of construction due to plastic
void former.
•Once on site quick installation.
NUIG School of Engineering
Wexford Opera House

16. Insitu Flat Slab
Composite Steel Frame and metal decking
Precast beams and Precast coffered slabs
NUIG School of Engineering
Wexford Opera House

17. Precast Concrete Voided Slab
NUIG School of Engineering
Wexford Opera House

18. Oran Precast, Oranmore, Co Galway
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31. Precast Concrete Beams & Double T units
NUIG School of Engineering
Wexford Opera House

32. Banagher Concrete, Banagher , Co Offaly
NUIG School of Engineering
Wexford Opera House

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40. Site Progress Photographs – Aug 2009 to Nov 2010
NUIG School of Engineering
Wexford Opera House

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44. Excavation & Replacement
NUIG School of Engineering
Wexford Opera House

45. Piling Operations – Set Out
NUIG School of Engineering
Wexford Opera House

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57. Concrete – Fairfaced Concrete
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71. Site Progress – Weather
NUIG School of Engineering
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81. Site Progress – November 2009 to March 2010
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