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HAMILTON ISLAND YACHT CLUB

Peter M. AllenMIEAust, CPEng, RPEQ

Opus International Consultants

Level 12, North Tower, 1-5 Railway Street, Chatswood NSW 2067

[email protected]

ABSTRACT

The iconic Hamilton Island Yacht Club and 35 Villas successfully withstood the

Category 3 Cyclone Ului last March, less than eight months after its official opening.

This paper describes the innovative, cost-effective structural solutions developed by

Opus to address the variety of competing architectural, geotechnical, environmental and

construction challenges presented at this remote Great Barrier Reef development. The

Architect conceived a nautical-shaped Yacht Club with slim terraces cantilevering up to

12.0m over the seashore and petal-shaped roofs that cantilever up to 11.0m, supported

on tree-columns. The Clients desire to bring international recognition to Hamilton

Island was surpassed.

Fig. 1: Rendered View of the Hamilton Island Yacht Club and Villas

Introduction

The Hamilton Island Yacht Club is the realisation of an incredible dream: a joint

venture between Hamilton Island owners, the Oatley family, and famed yachtsman Iain

Murray. They sought to create an internationally recognised facility using the stunning

concepts of exceptional Architect, Walter Barda, who envisaged an opportunity to go

for the big picture as a celebration of tropical, marine life and boat form, and the

drama of yachts taking on the natural forces of wind and water.

In 2007, Opus International Consultants (Opus) took up the challenge to push the

boundaries of structural engineering design for the dramatic sculptural forms of theYacht Club and 35 Villas. These unique structures enhance their beautiful location at

the entrance to the Hamilton Island boat harbour, with magnificent dual-water vistas
mailto:[email protected]:[email protected]


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over both the marina and Dent Passage of the Whitsundays, 20km off the Queensland

coast at the southern tip of the Great Barrier Reef.

The Yacht Club features an inspiring central atrium space, recreational and business

facilities over three levels, including contemporary indoor/outdoor restaurants and bars,

conference, theatre and function rooms and a private health club incorporating a marina-

front gymnasium, a 25 metre undercover lap pool and private cellar dining room.

The 35 luxurious Villas are nestled in two curled rows along the foreshore and hillside.

There are four Villa types, each comprising four bedrooms over four or five split levels,

some with plunge pools and basements. A crescent shaped lagoon pool and abundant

tropical landscaping complete the sites outstanding spectacle.

Structural Engineering Features

The structural engineers had to balance the competing demands of designing the Yacht

Club and Villas to withstand cyclonic winds and the aggressive seashore environment,

with Walter Bardas desire for streamlined nautical profiles, including extreme

cantilever terraces and roofs. Opus worked closely with the Client, Architect and

Contractor, Parkview Developments throughout the preliminary and detail design, and

construction phases to anticipate and resolve cost-effective solutions for construction,

transportation (road and barge) and erection issues particular to this remote tropical

island location. Walter Bardas Revit computer model was invaluable in understanding

the Architectural forms and consequently the development of the structural framework.

The modelling would continue to play this vital role through to the end of construction.

Foundations for the Yacht Club and Villas

There was a wide range of difficult ground conditions: The foreshore area was

comprised of poorly compacted hydraulically-placed fill mixed with rubble, which had

been dredged from the harbour decades before, on marine mud over ignimbrite, a hard

volcanic rock, up to 20m below. The rock rises to the hillside, in part an old quarry, but

generally covered by deep soil mixed with rock floaters. Together with the Geotechnical

Engineer, the most appropriate solutions for each particular condition were determined.

For most of the foreshore Villas, rather than piling to rock, a ground improvement

technique was adopted: 1.5m depth of the poor fill was removed and replaced by a Soil

Raft, comprising five 300 mm thick layers of quarry rock and clay mix on geofabric,

compacted to 98% SMD 2%. This mattress of controlled modulus engineered fill

enabled those Villas to be constructed with concrete Raft footings, which have since

settled only a few millimetres as predicted, without distress.The Yacht Club and the four Villas over the weakest mud were founded via vibro-

driven 12 to 22m long steel piles hammered into the underlying rock: 2500m (250

Tonnes) of 50 year-old recycled Dorman Long 24x7 RSJs were sourced from

Adelaide. The hillside Villas were supported on 400mm diameter auger piles to

bedrock, after floaters had been removed.

A Cathodic Prevention system was installed during construction to provide permanent

protection from corrosion of the steel piles, together with pile caps and other concrete

elements of the Yacht Club exposed to seawater.

Yacht Club Floors and Walls

To simplify construction of the irregular-shaped footprint of the Yacht Club floors, the

structural engineers determined an orthogonal framework for a conventionally-formed

concrete structure, with slab bands spaced at up to 8.0m centres between columns

spaced up to 10.0m centres. Spandrel beams were up to 900mm deep. The first level

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Peter M Allen

was formed on ground, with reinforced 450mm thick bands and 200mm thick slabs

designed suspended up to 8 metres between the steel piles.

The Architect required the three, free-form terraces on the second level of the Yacht

Club to cantilever up to 12 metres, much over water, whilst having them appear as slim

as possible (Refer Fig. 2). After considering a number of construction options, Opusdeveloped an internally post-tensioned in-situ concrete solution with both long and

cross-sections tapering from 900mm to 200mm thick, utilising elegant counteracting

keel-shaped pedestals. This met the stringent loading and exposure criteria, whilst

enhancing the nautical aesthetics of the building. The faceted formwork of the

cantilevers was built on temporary falsework, which was supported over the water on

piers, some of which were later utilised for the new marina boardwalk. 3D software was

used by specialist sub-contractor, Freysinett, to design and detail the post-tension cables

3 way tendons??.

Given these large cantilevers and long internal spans, the second and third levels were

post-tensioned. As the islands batching plant could only produce a maximum of 200m3

of concrete each day, seven and three pours were necessary for each floor, respectively.

The dynamic analysis of the vibration behaviour of the slender cantilevers indicated a

minimum natural frequency of 3Hz, and their satisfactory performance under crowd

loading was validated during the official opening and at numerous subsequent

functions.

Finite element analysis was utilised for the design of the dramatic 3-storey high walls

around the Yacht Club's central atrium. The walls are surfaces of a cylinder, cut and

offset in plan to enable the two sides to be tilted at 3 degrees and 7 degrees respectively.

The analysis permitted large openings in their 300mm thick reinforced concrete mass

that facilitated the slender sculptural elements desired by the Architect, while also

serving to anchor the perimeter roof structures against the extreme cyclonic winds

(Refer Fig. 3). The atriums presence is enhanced by the underside of its butterfly

shaped-roof, which also recreates the hull of a ship. The timber cladding hides a V-

shaped vierendeel truss-beam, designed under the central roof gutter to efficiently

support these roofs over the span of 19.0m and transfer their loads to tapered circular

columns at each end, which incorporate cast-in downpipes.

For minimal size, stainless steel RHS columns support the long, reinforced concrete

terrace above the lap pool.



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Fig. 2: Yacht Club 12m cantilever terrace Fig. 3: Yacht Club dramatic Atrium

Yacht Club Roof

As the Yacht Club is located in Region C - Terrain Category 2, the Basic Wind Velocity

was determined for serviceability as 45 m/s and for strength as 70 m/s (252 kph) in

accordance with AS 1170.1 Wind Loading Code. Numerous wind conditions from

several directions were modelled to assess the critical loading combinations on the

different walls and roofs. The maximum nett pressures on the cantilever portions of the

roof structures were calculated to be 6.4 kPa up and 4.7 kPa down and the maximum

local surface pressure 6.3 kPa.

The Yacht Clubs central butterfly-shaped roof, four perimeter petal-shaped roofs and

two external sails each cover an area up to 500m 2. Not deterred by these apparently

complex geometries, the engineers developed a consistent design that used the roof

shapes to structural and construction advantage. Their cross-section is generated from

the surface of a cylinder, so they adopted a curved steel vierendeel grillage, composed

of RHS members at 2.4m centres each way, largely 250mm deep x 150mm. Finite-

element analyses, both static and dynamic, confirmed that this steel framework is

vertically stiff and extremely rigid horizontally (Refer Fig. 4). It allows the roofs to span

up to 16.0m and cantilever up to 11.0m from column centrelines, while effectively

transferring the lateral loads from the roofs to the central walls, enabling the roofsperimeters to be supported on slender steel tree-columns (Refer Fig. 2). This design

also achieved the Architects requirement to keep structural depth to a minimum

between the copper roof cladding and the ceilings/eaves. A fire-engineered solution

allowed all of the CHS steel tree-columns to remain fully exposed, with some members

having intumescent paint applied to achieve required fire-rating.

Opus straightforward methodology for the detailing, fabrication, transportation and

erection of the roof framework was fully adopted by the structural steel fabricator, Gay

Constructions. The roof framing was designed so that it could be prefabricated as 2.4m

wide 'ladder-trusses' up to 15.0m long and shipped to the island, where they were

further site-welded into larger roof segments on the ground, prior to being lifted to their

final position for completion by in-situ welding and bolting. Whether the roofs aresupported on 'tree-columns,' or vertical posts, they meet at a variety of dispositions and

angles. This was simply resolved by incorporating additional straight 'rungs' in the

ladder frames where necessary, to rest on the CHS posts or 'branches.' Based on the



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Architects Revit model, the careful shop-detailing of the roofs using TEKLA software

resulted in no misalignments during construction of the steelwork.

Legend Ladder Frames Additional rungs Tree Columns

Fig. 4: Yacht Club Steel Roof Framing

The regular circular supports and straight lines of the roof surfaces generated by the

above geometry facilitated the installation of light-gauge, Topspan steel battens at

450mm centres, curved plywood and waterproof membrane, which underlay the copper

sheeting. The fixings, plywood and batten design was confirmed by Bluescope Lysaght

undertaking Standard Cyclone Testing at James Cook University, Townsville. In that

Dynamic Test of the prototype roof cladding, hundreds of fluctuating loads were

applied progressively as alternating positive and negative loads up to the ultimatepressure of 6.3 kPa, thus modelling the real, fatigue situation.

The southern 17.0m high, sail-like structure above the 'Bommie Restaurant' is framed

from a steel grillage that was delivered to the island as three prefabrications, to be

bolted together on site similar to the other roofs of the Yacht Club, and is clamped to

sloping curved reinforced concrete walls at its base.

Villas

Four basic Villa types were developed from a generic design, with individual Villas

being adapted as necessary to suit the various foundation conditions, terrain and

incorporation of basement and/or plunge pool options.After consideration of precast concrete and steel-framed structures, the most cost-

efficient methods on the difficult hillside terrain of the island were chosen: reinforced

concrete blockwork for the Villas vertical and lateral load-resisting structural elements

and a mixture of conventionally-formed beams and Bondek permanent steel formwork

slabs for their initial super-elevated floors. The complete structure was modelled using

ETABS finite element software (Refer Fig. 5). Where their overall height rose between

5 and 7 stories above ground, the super-elevated hillside Villas were laterally restrained

by ground anchors and/or steel cross-bracing to withstand the severe wind loads.

The Villa balconies, which cantilever up to 2.5 m, were supported on slender two-storey

raking columns of structural steel CHS, designed with cruciform tapers to highlighttheir finely-detailed pinned ends. Opus also developed a simple cast-in CHS detail to

support the intermediate balconies and to facilitate the different construction sequences

of some Villas (Refer Fig. 6).



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Peter M Allen

The Villas' upper terrace faade framework and S-curved steel roofs were prefabricated

on the mainland and completed on the island, as vierendeel grillages - similar in

methodology to that of the Yacht Clubs steelwork.

Environmental and Heritage Features

The Yacht Club building is designed for a 100 year life, utilising Cathodic Prevention

and hot-dip galvanizing of steelwork, while all exposed concrete has generous cover,

special mix and surface treatment to satisfy the aggressive marine environment.

Ground improvement of the dredged fill, as described above, reduced the length of piles

required for the project by approximately 2000m (200 Tonnes) of structural steel, which

is a huge saving in resources and transportation costs. Furthermore, the piles were

installed using a low noise vibratory rig and sourced from recycled steel sections.

Despite the 5 metre tidal range, the construction methodology ensured minimum

environmental impact on Dent Passage and the boatharbour, in accordance with the

requirements of Whitsunday local authorities and the Great Barrier Reef Marine Park.

The heritage lighthouse at the point of the breakwater was retained and complements

the development.

Conclusion

The project was officially opened by the Premier of Queensland at the commencement

of the annual Hamilton Island Yacht Race Week in August 2009. Less than eight

months later, in March 2010, Hamilton Island bore the full brunt of Category 3 Cyclone

Ului. The Yacht Club and Villas successfully withstood wind gusts in excess of 200 kph

with no structural damage, which was a testament to the buildings structural robustness

that is fundamental to, yet hidden within, its beautiful nautical shapes.

Some commentators have claimed that it is Queenslands rival to the Sydney Opera

House, with its dramatic architectural forms, clean finishes and superior functionality.

Already the Yacht Club is bringing international recognition, with its classic lines being

utilised as an emblem for Hamilton Island. It will be the focus for future Hamilton

Island Race Weeks and attract more yachtsmen and tourists from around the world to

this tropical island paradise.

Now that the astounding Hamilton Island Yacht Club has readily endured a severe

cyclone, not only has its structural integrity been validated and its longevity assured, but

its credit to Australian Engineering ingenuity is evident for the world to see.



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Fig. 5: ETABS Model of Hillside Villa Fig. 6: Hillside Villa Type D

ACKNOWLEDGEMENTS

Client: Hamilton Island Enterprises c/- Peter Schooley

Architect: Walter Barda Design Walter Barda, Adrian Esdaile and Michael Juda

Structural Engineer: Opus International Consultants Peter Allen and Luis Quispe

Geotechnical Engineer: David Dickson

Head Contractor: Parkview Developments Gareth Hodgins

Post-tension Sub-Contractor: Freysinett Tim Copeman and Slobodan Selenovic

Structural Steel Sub-Contractor: Gay Constructions Brendon Pike

Bluescope Steel Keith Johnston

Trend Magazine February 2010 Edition


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