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Wilkinson Eyre Splashpoint Leisure CentreWorthing

Splashpoint Leisure Centre byWilkinson Eyre Architects andengineer AECOM forms thecentrepiece of an ambitiousseafront regeneration schemein Worthing, West Sussex.Replacing the town’s ageingAquarena leisure centre, the£17m complex includes a six-lane 25-metre swimming pool,a combined learner/diving

The first of our special features onsteel construction,produced with Tata Steel and theBritish ConstructionalSteelwork Association,examines projects by Wilkinson Eyre and Arup Associates.

Externally, copper and redcedar cladding provide a sim-ple palette of self-finishedmaterials that are intended to age gracefully and requireminimal maintenance. Inside,exposed concrete, timber andceramic tiles provide tactilehard-wearing surfaces.

Structural designForming the structural heart of the project is a curving, multi-pitched pool hall with acomplex steel frame made by

pool, indoor leisure pools, ahealth centre, cafe and creche.The accommodation takes theform of ‘ribbons’ that flowfrom north-to-south, maximis-ing the available site and estab-lishing a connection betweenthe land and sea.

Evoking sand dunes, a sinu-ous roof profile reduces thevisual mass of the building andmediates the change in scalefrom the terraced houses thatline the coastal road to theopen sea beyond.

Structural spans between thelongitudinal ridges widen asthe height of the structureincreases towards the sea, ter-minating in a series of glazedfacades overlooking the water.“The scheme occupies a promi-nent location on the seafront,but rather than dominating thesite in the style of a grand sea-side pavilion, it sits informally,even playfully, within its set-ting”, explains Wilkinson Eyredirector and project architectSebastien Ricard.

Top View from the beach, interior, andgable end (phs: Julian Abrams). Above Site plan.Left Steelwork moment frame model; software employed in the steelwork designincluded Nemetschek’s Scia Engineer andRevit 3D (ph: AECOM).Right Frame construction (ph: AECOM).

Severfield (UK). Supported by305x305mm universal steelcolumns spaced at between 5-and 12-metre centres, the pri-mary roof structure comprises aseries of 1.3-metre-deep, asym-metric, double-curved steelplate box girders. The beamsspan 50 metres longitudinally,allowing uninterrupted views ofthe diving and competitionpools from the spectator gal-leries above. They also supportsteel-framed clerestorey glazingthat runs the length of the hall.

Lateral bracing between thebeams is provided by slender100mm square hollow sectionsat 3- to 8-metre centres. Aspruce plywood deck is locatedbetween the primary beams,presenting a ‘clean’, unclut-tered soffit to the pool and sup-porting the roof insulationabove. An innovative stabilitysystem formed from steel strutsand moment frames eliminatesthe need for conventionalbracing, which would havevisually interrupted the glazed

facades. Artificial lighting isfixed to the column casingsand walls. A subterraneanplenum provides air distribu-tion to the pool hall.

Steel specification“The use of steel was funda-mental to achieving the archi-tectural concept”, says structur-al engineer and AECOMregional director MatthewPalmer. ‘Steel not only allowedus to achieve 50-metre clearspans, high-level clerestorey

STEELsolutions

in association with

STEEL SOLUTIONS

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Project teamArchitect: Wilkinson Eyre Architects;structural, civil, m&e engineer, fire,acoustics, transport, access, environ-mental: AECOM; steelwork contractor:Severfield (UK); main contractor:Morgan Sindall; client: WorthingBorough Council; photos: Julian Abrams.

glazing and transparent gables,it also gave a ‘lightweight’appearance favoured by thedesign team. Another advan-tage is steel’s ability to achievetight construction tolerances.These were essential for theinterfaces with the glazing, cop-per cladding, and timber roof-ing. The latter was machine-fabricated in Germany and

required a 5mm installation tol-erance. Last but not least, steelprovided the benefits of areduced on-site programmeand the avoidance of wettrades.”

Detail design “The double-curved asymmet-ric beams are subject to biaxialbending, axial compression

and torsion, as the complexgeometry gives rise to a rangeof imbalanced wind and snowloads”, explains MatthewPalmer. “Analysis involved first-principle checks, customspreadsheets, and finally a fullnon-linear finite element inves-tigation of the entire structure,to accurately predict the forcesand movements.”

Nemetschek’s Scia Engineersoftware was used to exploreand optimise cross-sectionalproperties, as well as calculatethe precambered deflections.A detailed model of the beamconstructed as a series ofplates was also used to investi-gate distortional deforma-tions. Movement joints weredesigned into the clerestorey

structure to reduce axial loadsposed by Vierendeel action.

Coordination of the designwas undertaken using 3D RevitCAD models, with the archi-tectural, steelwork and timberfabrication models overlaid forearly clash detection. Thishelped to reduce both theoverall cost of the project andpotential delays on site.

FabricationSamples of each of the mainbeams were fabricated to pro-vide quality benchmarks.Flush-finished shop- and site-welds provide the exposedstructure with clean, uninter-rupted lines. Thorough geo-metric checks were madethroughout the fabricationprocess to ensure that the

complex geometry wasadhered to. Exposed steelworkin the highly corrosive poolenvironment required a275µm, three-layer paint sys-tem, which is guaranteed for alife-to-first-maintenance of 20years. Fire protection was notrequired as the steelwork pro-vides the roof and facadestructure only.

ErectionThe complex load-pathsrequired a detailed plan forthe erection sequence. An 800-tonne crane was used to liftthe 50-tonne main spans intoplace, while a second lightercrane was used to connect thelateral and torsional retraints.Site welding was limited to themidspan of the two primarybeams, with bolted splicesused elsewhere. This reducedthe installation time andimproved site safety. High-grade stainless steel fixingswere used to support the tim-ber roofing panels. “The fabri-cated structure was deriveddirectly from the coordinated3D model and fitted togetherperfectly on site – an impres-sive achievement, consideringthe complexity of the ridges,curves and steps”, commentsMatthew Palmer.

STEEL SOLUTIONS

Top The steel frame during construction(ph: AECOM); exterior and interior views(phs: Julian Abrams). Left Ground, first and second floor plans;cross sections.

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ENTRANCE

CAFE RECEPTION

ADMIN ADMIN

PIAZZA

DIVING/LEARNER POOL

COMPETITIONPOOL

LEISUREPOOL

CHANGING CHANGING

TREATMENTROOM

STUDIO

STUDIO

HEALTH &FITNESSSUITE

LAZYRIVER

TERRACE

SAUNA

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Arup AssociatesEngineering & ComputingCoventry University

Arup Associates’ Engineering& Computing Building (ECB)at Coventry University is alandmark project combiningeducation, industry andresearch facilities in a single,state-of-the-art building. RatedBREEAM Excellent, the16,000-square-metre schemeincludes an engineering centrewith flight simulators andengine test cells, a wind tunnel,workshops, lecture theatres,classrooms, interactive com-munal spaces and offices.

Intended to represent theduality of science and nature,the plan consists of two

interlocking L-shaped struc-tures organised around a land-scaped courtyard. The three-storey Nature block to the southemploys a simple glass envelopewith an extensive green roof. By contrast, the seven-storeyScience block to the north has a highly engineered cantedfacade comprising a lightweighttimber frame and aluminiumcomposite cladding panels.Hexagonal windows shaded byprojecting aluminium hoodsallude to the architects’ con-cept of a ‘busy colony’.

Central to the environmentaland spatial concept is theInteractive Zone. This is locatedbehind the inclined ‘shop win-dow’ facade and forms the public and educational heart of

the building. Structured usingan expressive steel frame, thetriple-height space contains themain circulation and breakoutspaces, while also providing con-trolled daylighting and naturalventilation. The flexible, open-plan layout is designed to fostercollaborative learning and thecross-fertilisation of ideas.

Structural designComprising a lattice of horizon-tal box beams and diagonalCHS struts, the steel structurenot only supports a series ofpod-like breakout spaces, butalso provides lateral restraintfor the atrium facade and addi-tional compressive support forthe transfer structure at third-floor level. “We chose steel

because its inherent strengthallowed us to create an aesthet-ically pleasing structure usingrelatively small sections”, saysstructural engineer RobertPugh of Arup.

Detail designThe apparently random grid ofintersecting and non-intersect-ing diagonal steel struts is gen-erated both by the desire toavoid running them past thehexagonal window openings,and by the locations within theatrium of the pods, which areof different sizes and have pre-cisely defined geometrical rela-tionships to each other.

Inclined in two directionsand varying in diameter from114mm to 244mm, the circularhollow sections are connectedto each other and the horizon-tal box beams using continuousfillet welds. “We didn’t want thestruts to be of uniform size”,says Pugh. “Instead, each onecorresponds to the structuralrole it is performing. This isreinforced by printed labelsattached to each section, whichinform students of the forcesacting on the members.”

STEEL SOLUTIONS

Above Facade details (phs: Simon Kennedy).Left Upper-ground and first-floor plans. Right Interior view; air-flow diagram show-ing how thermal mass is employed to helpmoderate the internal environment.

Spanning across the internalface of the inclined atriumfacade and corresponding inposition to the floor slabs are 450x250mm rectangularhollow sections. These aredesigned to balance the diago-nal forces in the structure(emanating from the struts),and provide lateral bracing forthe self-supporting atriumfacade. They also serve as edgebeams for the breakout pods.

The steel structure of theInteractive Zone is bolted backto the rest of the buildingusing steel base plates weldedto the ends of the sections.“Some of the shear forces pro-duced by the diagonal strutswere reasonably large. Thisnecessitated plates measuringtypically 500 by 500mm to pro-vide adequate spacing for up tosix anchor bolts”, explainsPugh. Projecting steel connec-tion plates welded to the outeredge of the beams allow theinner face of the engineeredtimber facade frame to be bolt-ed to the steel structure witharticulation for vertical differ-ential movement.

Autodesk’s Revit Structuresoftware, coupled with OasysGSA, was used to model andanalyse the design, which wasthen was transferred to Teklasoftware for steelwork contrac-tor Traditional Structures toproduce the fabrication modeland shop drawings. “We evenconsidered painting the steelsections the same colours asthose expressing different axialloads in the General StructuralAnalysis software contour plot”,recalls Pugh, “but the architectfelt this would overcomplicatethe atrium in visual terms.”

Fabrication/erectionThe steel sections, including anumber of factory-weldedcomponents comprising sever-al intersecting elements, wereassembled on site using a smallmobile crane. Erection tooktwo weeks, after which theframe received an architectur-al-quality, silver-coloured, thinintumescent coating.

Project teamArchitect, structural and service engineer:Arup Associates; steelwork contractor:Traditional Structures; main contractor:Vinci Construction; client: CoventryUniversity; photos: Simon Kennedy.

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STEEL SOLUTIONS

Weighty mattersThermal mass has the potential to lowerenergy consumption,but its use isn’t limited to heavy construction methods.

Above The Woolwich Centre, by architectHLM, is designed to achieve 50 per centcarbon reductions. The steel frame com-prises fabricated beams that supportexposed, precast concrete vaults on theirbottom flanges. The mixed-mode ventila-tion strategy utilises the glazed facade.When needed, extra convection coolingcan be provided by passive chilled beamsthat hang within the vaults (phs: DianeAuckland/Fotohaus).

Left 3D Reid’s Co-operative GroupHeadquarters, Manchester, features 16.5msteel beams supporting precast concretecoffer units. Three large earth tubes tem-per the air entering the building, which isdistributed by a passive stack system.

Further complications canarise because of diurnal andseasonal changes in externalconditions. For instance, thebuilding may sometimes berequired to contain heat,sometimes capture it, andsometimes reject it. Night-time cooling can be

achieved in a number of ways.Natural ventilation is the mostconsistent with environmentalsavings, though often somemechanical control of shutterswill be required. Employingnatural ventilation to cool thethermal mass can also raiseissues such as security of open-ings, ceiling finishes, acousticneeds and services distribu-tion. Other cooling optionsinclude mechanical ventila-tion, ideally integrated with abuilding management system,and cooling of slabs from with-in using piped water or ductedair. Other, more complexdesign strategies that employground energy systems includethermal labyrinths, as at 3DReid’s Co-op Group headquar-ters in Manchester.

Further reading Tata Steel andthe British ConstructionalSteelwork Association (BCSA)have recently published TheSteel Construction ThermalMass Supplement, which exam-ines fabric energy storage andsustainable strategies (seewww.steelconstruction.info).

Thermal mass or fabric energystorage – the capacity of a mate-rial to absorb, store and releaseenergy – has the potential toreduce energy use in buildingsby smoothing out fluctuationsin conditions above or belowcomfortable ambient levels. The ability of a material to

absorb or release heat throughthermal cycles is based on itsthickness, thermal capacity andconductivity, surface resistanceand density. Typically, concreteand masonry work well, absorb-ing heat from the air as thetemperature rises and releasingit when it falls, and this can beharnessed in either a heatingor cooling mode. The surfaceof the material must be suffi-ciently exposed to allow heattransfer, and the greater areaexposed, the greater the bene-fits in terms of thermal mass. Ifthe mass is to absorb heat, the

precast concrete. The resultsdemonstrated the effectivenessof the thermal mass – in allcases the peak temperaturesremained below 28 deg C for atleast 99 per cent of the occu-pied hours, suggestingmechanical cooling methodscould be avoided, and implyingthat little additional benefitwould be gained by providingadditional thermal mass.Significantly, these results wereconsistent with other researchshowing that the optimumthermal mass gain can beachieved as long as 75-100mmdepth of exposed concrete slabis available. However, the studyalso noted that the perform-ance of glazing, in terms ofcooling load, could be as signif-icant as benefits from usingthermal mass – ie using highperformance solar control glaz-ing rather than standard clearlow-e glass (with 40 per centglazing area). In designing buildings to

exploit thermal mass, factors

that may require considerationinclude: what conditions areneeded in the particular build-ing type; do heating or coolingloads (or both) require con-trol; and how might the build-ing fare in relation to climatechange predictions? Moreover,conventional wisdom suggeststhat thermal mass is more suit-ed to buildings with regularoccupation, such as offices. Thermal mass strategies can

be hampered if natural ventila-tion is not viable for example,because of orientation,acoustics or air quality, or ifareas are compartmentalisedor air-conditioning is needed.

STEELCONSTRUCTIONThermal Mass

Thermal mass key points:• The maximum thickness of concrete useful

for thermal mass is 75-100mm• Available thermal mass is already maximised

in standard floor slabs as thicknesses greater than 100mm will be provided

• Upper floors in steel- and concrete-framed multi-storey buildings are typically concrete

• Effective thermal mass solutions are independent of structural frame material• Exposing floor soffits for thermal mass

can have constructional impacts and costs

interface is better on ceilingsoffits and higher walls.Unsurprisingly, suspendedceilings and drylining canreduce heat transfer. Typically in the UK, through

a daily thermal cycle, only100mm of a concrete floorslab is available to absorb anddischarge heat energy. Thispotential for thermal mass istherefore already maximisedin standard floor slabs, whichwill typically be 200-300mmthick for structural design pur-poses. Increasing the depth ofthe slab simply adds weight,which impacts on resourceefficiency without increasingthermal mass performance. In multi-storey buildings, the

upper floors are the mostimportant elements in termsof providing ‘accessible’ ther-mal mass. Whether a buildingis steel or concrete framed, theupper floors are generallyeither made of cast in-situ orprecast concrete, and there-fore the potential to use thethermal mass of the upperfloors is not restricted by thechoice of framing material.Consultant AECOM’s study

‘Thermal Mass in CommercialBuildings’ (2008, for TataSteel) modelled the coolingpotential of five different floortypes with fully exposed soffitsin a naturally-ventilated four-storey office building –Slimdek, composite floor slab,precast concrete, reinforcedconcrete and hollow-core