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Steel SolutionsComplex curves at the FrancisCrick Institute in London, by HOK and PLP Architecture, and Slough Cultural Centre by Bblur,plus new guidance on steel andembodied carbon from Tata Steeland the British ConstructionalSteelwork Association

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TopConstruction in progress, May 2014.The 85,935sqm building sits on a 1.5hasite behind the British Library. Onethird of the building is below grade, in a 16m-deep basement. A double-curved steel-framed roof encloses twoplant stacks – one of three storeys,and the other of two. The two halves of the roof overlap above the atrium(phs: Wellcome Images courtesy ofLaing O’Rourke).

AboveThe louvre-clad roof is open to allowair circulation around the plant stacks.

LeftCGI of the east elevation (ph: Wadsworth 3D).

HOK and PLP ArchitectureThe Francis Crick Institute

Accommodating 1500 staff and comprisinglabs, teaching space, offices and publicspaces, The Francis Crick Institute is amajor biomedical research facility, due to open later this year in Somerstown,central London. It was designed by HOK, with PLP Architecture invited tocollaborate on the development of theexternal massing and to act as designer for the building envelope.

The body of the building comprises twolong laboratory wings that run east to west separated by a g lazed-ended atriumthat flares out spectacularly to the east.The southern wing consists of ground plusfive storeys, the north, ground plus fourstoreys. The wings are bisected by a north-south atrium dividing the building intofour distinct science ‘neighbourhoods’. The resulting cruciform atrium introducesdaylight deep into the laboratoryquadrants through its g lass roof and fourglazed end walls, offering views into theworkings of the building from the externalpublic spaces.

The base of the building, containing publicand social spaces, is extensively g lazed tolink the interior and the exterior. Walkwayslinking the north and south quadrantsanimate the east and west walls of theatrium above the two principal entrances atground level. The laboratory blocks andsolid areas of the facade at the lower levelsare wrapped in mortared terracotta inreference to neighbouring buildings.

Above the laboratory wings sit the twovast vaulted louvre roofs which echo theroof of St Pancras Station’s historic BarlowShed at the opposite side of Midland Road.These roofs enclose the large plant volumesthat are required to service a building ofthis nature. The southern roof shellincorporates one of the country’s largestbuilt-in photovoltaic arrays. On the east andwest approaches, the roof shells cantileverbeyond the facades below to denote theentrances and to create a strong, welcomingarchitectural statement.

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Curved roof form

The roof form is derived from a parametricmodel which allowed many iterations to betested quickly for form-finding, street viewassessment and clash detection. It wasconstructed using basic mathematicalelements such as coordinate systems,planes, points, lines and arcs, arc-compositecurves and surfaces.

The generated roof surfaces are flat,single-curved or double-curved. The latterare part of a torus – their curvature in onedirection is constant and the key establishedsurface is the exterior face of the steelstructure. Everything outside of this is the‘facade’ build-up. The model simplified theprocess of producing elevations and sectionsnecessary to describe the building, and wasused by structural engineer AKTII toestablish the steelwork set-out.

The underlying structure of the roof ispainted steel, hooped in the north-southdirection and gently curved in the east-westdirection. This grid is braced back to themain building frame for stability and iscapable of large cantilever overhangs at theeast and west ends and on the north side ofthe higher roof.

Steelwork contractor Severfield (UK) wasresponsible for the connection design andfabrication of around 2,300 tonnes ofstructural steelwork.

East entrance wall and canopy

The eight-storey-high east atrium facade hasa primary structure of tubular steel sections,with vertical members at six-metre centres,and at each floor level, wind loads are takenback to the cross-atrium bridges which actas a beam in plan. All structuralpenetrations through the facade arethermally broken using high-load isolatorplates. The weather skin is 5.08m-highdouble-g lazing fixed back to vertical g lassfins at 0.75m centres spanning floor tofloor. The fins are predominately on theoutside of the glazed wall, but where theatrium facade abuts the main body of thebuilding, the system reverses with the finsbeing on the interior. This leads to anunusual detail where the glass fin becomespart of the thermal envelope, which isachieved by adding a further layer of g lassto make it a double-g lazed unit.

At low level, the facade includes g lassrevolving door drums, pass doors andglazed make-up air vents. A large laminatedglass canopy is supported off the primarystructure via plate beams and tubularsuspension members through the glazedfacade. The canopy is 19m wide and 7mdeep, reclining back to a gutter concealed inthe offset between the facade glazing atground and first floor.

BelowEast entrance wall and canopy: mock-up of cruciform tubular section ofprimary steel structure; constructionof facade with primary steel structuregrid of tubular sections with atriumbridges acting as a structural beam;section, elevation and plans of primarysteel structure comprising vertical andhorizontal CHS profiles, aluminiumcarrier frame and double-g lazed units;detail axonometric of g lass panes andframework of horizontal CHS steelprofiles with anodised aluminiumcarrier frame (phs: PLP Architecture).

Top rightConstruction of steel roof hoops in thenorth-south direction. The visiblesurface of the roof is a kit of differentlouvre blades, attached via transversebrackets to an extruded aluminiumtubular spine spanning between themain steel hoops. These include solidand perforated aluminium andlaminated glass blades, all of differentwidths, and photovoltaic blades, allangled at 15 degrees to the tangent ofthe hoop to which they are fixed. The east and west oversailing bladeswiden and flatten towards their endsto form a continuous curved roof edge.The twist is achieved by simplyrotating the blade brackets around the central spine (phs: WellcomeImages courtesy of Laing O’Rourke).

Bottom right3D composite model of roof louvres,photovoltaic array, steel structure andbase of building.

Key

1 Horizontal steel support structure

2 Stainless steel shoe bracket

3 Motorised fabric roller blind

4 Stainless steel blind guide rod

5 Laminated double-g lazed unit

6 Anodised aluminium carrier frame

7 Laminated glass fin

8 Internal bridge link

9 Spiral fin radiator

10 Thermally broken structure

11 Steel cruciform beam

12 Vertical steel support structure

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Selected suppliers& subcontractors

Curtain wall andenvelope contractorScheldebouw with JosefGartnerSteelwork contractorSeverfield (UK)LouvresLevolux

Project team

ArchitectHOK with PLPArchitectureStructural engineerAKTIIServices engineerArupFacade engineerEmmer PfenningerPartnerMain contractorLaing O’RourkeClientThe Francis CrickInstitute

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Project team

ArchitectBblur architectureStructural engineerPeter Brett AssociatesLandscapeSpaceHubBroadway MalyanInteriors CZWGSteelwork contractorCaunton EngineeringMain contractor Morgan SindallConstructionClientSlough Borough CouncilMorgan SindallInvestments

Bblur ArchitectureSlough Cultural Centre

Due to complete in the spring, SloughCultural Centre by Bblur Architecture andengineer Peter Brett Associates is aflagship community building forming partof the £450m Heart of Slough regenerationscheme. Conceived as a covered streetlinking two new public squares, the three-storey structure is fully g lazed at eitherend and features a concave northernelevation that is curved in two directions.The internal accommodation includes alibrary, gallery, a multi-purposeperformance space, classrooms andmeeting areas.

Belying its complex fan-like shape, thebuilding employs a regular 7.5 metrestructural grid, with only the double-curved north facade constructed ‘off-grid’.‘We chose to build in steel primarily forreasons of cost and speed’, says Bblurpartner Matthew Bedward. ‘Steel alsoallowed us to achieve a sculptural formwith relative ease and within a reasonabletime scale.’

The primary structural frame comprises273mm diameter CHS columns supporting406x178mm universal steel beams, with350x127mm joists at 2.5 metre centres.

The north elevation, which follows thecurving perimeter of St Ethelburt’schurchyard, adopts a ‘long arch’ solution tominimise the number of columns that canbe seen through the ground floor curtainwall. The aim is to strengthen the visualconnection between inside and out, whilealso giving the structure an elegantlightweight appearance.

Taking the place of the ground floorcolumns are a series of primary, curved steelI-sections, which are supported by apropped, single radius, 324mm diameterCHS arch that spans almost the entirelength of the facade. Closely spaced atalternating vertical centres of 1.1 metresand 2.2 metres, the 152x152mm facadesteels form a rigid ladder frame thatfacilitates fixing of the external metal skinand double-g lazed units with the minimumneed for secondary steelwork. The 3mmthick polyester powder-coated aluminiumcladding panels are curved only in thevertical plane. The horizontal curve will be achieved through faceting, with theshallowness of the radius ensuring a smooth unbroken appearance.

The project was procured using BIM, withBblur coordinating the master 3D CADmodel, and assuming responsibility for allsetting out, including the steel structure andservices. The model was supplied tospecialist steelwork contractor CauntonEngineering relatively early in the detaildesign process. Liaising with the architectand engineer, the company developed itsown fabrication-based model, which wassubsequently fed back into the mastermodel and used for clash detection.Bedward describes the process as ‘seamless’,resulting in a high degree of coordinationbetween the steel structure, services andexternal skin.

The steel frame was erected in threesections, starting at the east end of the planand working west. Resembling a ‘kit ofparts’, the frame was bolted together using acrane and cherry picker over a period offour months. The 60 metre long CHS archcomprises three separate sections, whichwere spliced together on site andtemporarily propped while the curvingvertical I-sections were bolted to flangeswelded to the top face.

Top Structural BIM model with matchingview showing completed steel frame.

AboveThe steel structure was erected inthree phases – starting from the east end of the plan and workingwest –over a period of four months.

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Sustainability with SteelCalculating Embodied Carbon

The significant reduction in operationalcarbon emissions from buildings over thepast decade, achieved primarily throughbetter energy efficiency, has led to anincrease in the importance of embodiedcarbon impact. The most straightforwardway to measure the embodied carbonimpact of construction materials andproducts is to calculate it using rates ofkgCO2e/kg. The key of course is inidentifying the correct rates to use.

Lifecycle assessment (LCA) is generallyused to determine the embodied carbonimpacts of construction products, but thismust be consistent and rigorous to beuseful as a tool for comparison, andshould ideally follow the lifecycle stagesset out in BS EN 15804. Somemanufacturers present data based on‘cradle-to-gate’ data that takes intoaccount only impacts from extraction andmanufacturing, while others consider allthe lifecycle stages of BS EN 15804 –‘cradle-to-cradle’ data.

Clearly comparing cradle-to-gate dataagainst cradle-to-cradle data will result in a flawed analysis. Architects shouldtherefore check with the relevantmanufacturer how its data has beenderived. Comparisons based on kgCO2e/kgof material should be avoided as differentmaterials are not used in the samequantities within a building to deliverequivalent performance. As a minimum, a kgCO2e/m2 assessment should be used in considering the effects of materialintensity in the ‘as built’ condition. SCI Carbon Footprint Tool

A carbon-footprint web tool developed by theSteel Construction Institute (SCI) enablesdesigners of multi-storey buildings toestimate the embodied carbon of a buildingsuper-structure. The tool, available online atwww.steelconstruction.info, can be used in‘auto-generate’ mode, whereby the basicgeometry, structural grid and floor system areused to estimate material quantities usingalgorithms developed by the SCI for commonstructural steel solutions. Alternatively, the‘manual input’ mode allows entry of actualmaterial quantities. To compare the impact ofa steel-framed building with a concrete-framed building, the web tool should be runseparately for each option. Appropriatecarbon emission factors are then applied tothe material quantities to estimate the overallfootprint. Results are presented as a CO2efigure for the whole building and per squaremetre of floor area, and a bar chart indicatesthe contributions of the frame, cores, floors,roof, fire protection and void walls.

Sheppard RobsonOne Kingdom Street

Sheppard Robson’s 10-storey officebuilding at Paddington, west London, wascompleted in 2008 and employed in TargetZero, a research project by AECOM, SweettGroup and the SCI intended to provideguidance on the design of low- and zero-carbon non-domestic buildings.

The building has a steel frame on a12x10.5m grid, with cellular steel beamssupporting a lightweight concrete slab ona profiled steel deck. The larger span isdictated by the location of beams withinthe Crossrail podium deck on which theyare supported. The foundations comprise750mm-diameter bored piled foundationswith in-situ concrete pilecaps restrainedlaterally by the ground beams. The pilesare the same size as those used to supportthe existing Crossrail podium to reducepotential differential settlement arisingfrom the use of different pile diameters.

The embodied carbon impacts for twooptions were considered on a cradle-to-cradle basis: the as-built steel compositedesign and a concrete alternativecomprising 350mm post-tensioned flat-slabconstruction. For frame and floors, thesteel composite option has an impact of152kgCO2e/m2 compared to 190kgCO2e/m2

for the post-tensioned concrete option thatis 24 per cent greater.

The lighter superstructure for the steeloption also results in smaller foundations.Consequently, the impacts from thesubstructure are different for each option.The foundations for the composite steeloption have an embodied carbon impact of59kgCO2e/m2 compared with 74kgCO2e/m2

for the post-tensioned concrete option, anincrease of 26 per cent. When consideringthe building as a whole, steel compositehas an embodied carbon impact of452kgCO2e/m2, which equates to a total of14,937tCO2e. This compares to the post-tensioned concrete’s impact of506kgCO2e/m2, which equates to a total of16,716tCO2e, or 12 per cent greater.

Comparative costs were also examinedas part of the study. For the frame andfloor costs alone, the steel compositeoption is £316/m2 compared to £377/m2

for the post-tensioned concrete alternativethat is 19 per cent more expensive. Whenconsidering the total building costs, thesteel composite option is £1869/m2 or£61.7m compared to £1941/m2 or £64.1mfor the post-tensioned concrete option. Theconcrete alternative is therefore four percent more expensive than the steel option.

End of Life Dataset

Stuttgart-based sustainability consultant PEInternational has developed an end-of-lifedataset that compares embodied carbondata for commonly-used framing materialson a cradle-to-cradle basis. The data coversdemolition and recycling impacts (modulesC and D to BS EN 15804). Data for all thematerials included can be viewed online atwww.steelconstruction.info, along withsources for the cradle-to-gate (A1-A3) data.Designers using this dataset can haveconfidence in its transparency, robustnessand consistency, enabling comparisonbetween different frame options to beaccurately and effectively carried out onany project.

Above, rightOne Kingdom Street is 40m high and81x45m in plan. It accommodates24,490m² of open-plan, 2.8m floor-to-ceiling office space on 10 floors and, onthe eastern half of the building, twobasement levels with car parking andstorage. The gross internal floor area is33,018m². The building has three coresand two central atria on its southelevation which house six scenic wallchamber lifts. A typical office floor plateprovides approximately 2,500m² offlexible space on a 1.5m planning grid.

Further detailsSteel Construction – EmbodiedCarbon, a guide published by TataSteel and the British ConstructionalSteel Association is available from:www.steelconstruction.info.