Friday 26/07/2013 In association with The British Friday 26/07/2013 www.bdonline.co.uk 12 STEEL FOCUS 20 Constructional Steelwork 13 www.bdonline.co.uk Association and Tata Steel

The wider floor plates on upper storeys maximise lettable space with views The talk over the city. of the town Rafael Viñoly’s Walkie-Talkie is now flaring out over the skyline, thanks to 13,000 tonnes of structural steel and 37 unique floor plates Text by Pamela Buxton

roclaimed on its hoard- ing as “the building with more up top”, Ra- fael Viñoly’s 177m-high tower 20 Fenchurch 2 PStreet is rapidly taking shape on London’s skyline. Now almost fully clad, the 64,140sq m tower 1 3 is due for completion next year. The ’s controversial, distinctively flared shape — less like its nickname Walkie-Talkie and more like a pint glass — has been realised with the use of 13,000 tonnes of structural steel provided by steelwork contractor 4

William Hare. i m age : Rafae l V ñoly Ar c h itects With such a distinctive form, this building will always divide aerial perspective opinion as it joins the growing number of unconventional tow- 1 2 Fenchurch Street 3 20 Fenchurch Street 4 ers now jostling for attention in the capital’s financial heartland. a publicly accessible sky garden lution to a tight 38-month time- North section: 20 Fenchurch Street’s pint-glass profile is created as the floor plate West section: The steel frame cantilevers after the 25th floor. The upper three Viñoly maintains that the design with spectacular views over the table was only possible, accord- flares and then tapers back on the upper storeys. storeys are taken up with the sky garden. — criticised by some as over- City. ing to Canary Wharf Contractors whelming — respects the City’s The tower’s form presented associate director Charlie Paul, Each beam was kept to a In order to avoid using the three historic character by “following a tough challenge for engineer with the use of what he terms 4D 600mm depth whatever the tower cranes needed to erect the the contour of the river and the Halcrow Yolles and contractor BIM modelling — the fourth di- span, except at the uppermost structure during the worst of the medieval streets”. Canary Wharf Contractors since mension being time. This gives levels where they were increased winter weather, Canary Wharf Commercially, the swelling each floorplate was a unique complete coordination of all as- to 1,150mm. All are fixed to the Contractors asked William Hare form makes sense, maximising shape and size due not only to the pects of design and construction concrete core using embedment to deliver the steel installation in the footprint by creating larger widening floor plates but also the using software compatible with plates. Most are fabricated plate just 36 weeks from May 2012 to floor plates as the views get bet- concave curve on the north and the Revit programme used by the girders with web penetrations to January 2013, rather than 41, by ter. And at the very top, the joint south elevations and the convex design team, Sketchup Pro used accommodate services within the working on accelerated hours for i m age : Rafae l V ñoly Ar c h itects developers Land Securities and curve on the east and west. by the contractor and Tekla used beam depth. Typical floor beam 17 weeks. This included the instal- sky garden promise Creating and delivering the so- by the subcontractors. spans range from about 11m at lation of the approximately 8,500 This real-time model allowed level 2 to 18m on the upper levels. major structural members that The sky garden is a 50m x the contractor to fully coordinate According to Guneratne, the made up the steel frame. 60m, double-height glazed the design team and specialist geometric changes were the crux Having installed the verti- space at the top of the contractors so that they could an- of the structural design challenge. cal cladding, the contractors are tower with clear spans and ticipate any clashes and hiccups “Architectural aesthetics were the now building the sky garden. a giant full-height window within the various interfaces dur- main driver. When the shape of When complete in April 2014, the on the north and south ing the construction programme the building changes, it funda- Breeam “Excellent” building will elevations. and act accordingly to eliminate mentally changes every beam a contain 61,000sq m of offices up to The original intention them. In this way, it also enabled little bit. So we formulated an the 34th floor as well as 1,200sq m had been to use a space- those tendering to give a more ac- algorithm that automatically re- of ground floor retail, plus the sky frame construction but this curate price, according to Paul. calculated the positions of all the garden, which is intended to be a was changed to a more “We had very little argument beams on every floor.” public space with bars and restau- economical and faster-to- and debate with William Hare. Bifurcating columns were rants served by its own dedicated erect portal frame with 34 The modelling we did allowed us initially considered in order to lifts. structural fins spanning to have a much closer relation- achieve the flaring shape but this Development costs for 20 Fen- east to west, including ship,” he adds. would have taken up too much church Street will total £239 mil- two central 20m sections Steel was the only viable choice space within the plan. Instead, lion. So far, with completion still a 1,200mm deep. Each is for 20 Fenchurch Street’s struc- the solution was to facet the steel year away, office accommodation fixed by William Hare into ture, lowering the weight of the structure up to the 25th floor, with is 56% pre-let. a base connection — a

p ho t o: w i ll ia m h a r e building and allowing the engi- the facets occurring first every six concealed steel “shoebox” neers to use existing foundations floors, then every four and finally typically 750mm x 400mm faceted structure on the site, according to Halcrow every two on areas of high curva- x 100mm deep. This takes To create the flared shape the columns are faceted up to Yolles buildings team lead Jason ture as the tower neared its widest PROJECT TEAM the horizontal forces the 25th floor, after which the top of the flare is achieved Guneratne. It also met the re- “bulge” point on the 27th floor. Developers Land Securities, into the steel structure with a cantilever, both of which simply delivered the desired quirement for long spans in order However, the maximum beam Canary Wharf Group and accommodates profile. The angle of the columns is changed in a concealed, to maximise lettable office space. span that could be tolerated was Architect the transition from the bespoke spigot connection welded to the top of each column The structure consists of 22 box 20m. So from level 25, the struc- Rafael Viñoly Architects aluminium fins running up during fabrication. This allowed the next column to be columns arranged on a 9m grid ture’s flare was created using a Executive architect the side of the tower into positioned at the correct angle to achieve the facet while around a central core. Columns cantilever to give the final 4m on Adamson Associates the steel roof structure. avoiding the need for an external flange. The impact of were constructed from fabricated the north and south faces beyond Structural and facade engineer Mitre connections on the bolt head is minimised by the fire-protective covering. sections ranging from 525mm x the column line. On the east and Halcrow Yolles the four corner fins are

With such complex column geometry, the use of 3D project 525mm square box sections with west sides, the columns remain in Contractor i m age : Ha l c row Y oll es also accommodated information was hugely important, according to steelwork 100mm-thick plates to 525mm x the facade, which is triple-glazed Canary Wharf Contractors in more heavily loaded contractor William Hare. 350mm I sections with 40mm- with panelised aluminium clad- Steelwork contractor The steel frame is made up of approximately 8,500 major “shoeboxes”.

thick plates at higher levels. Pho t o: Jon C a rdw e ll ding and vertical louvres. William Hare structural members. Friday 26/07/2013 In association with The British Friday 26/07/2013 www.bdonline.co.uk 14 STEEL FOCUS university of winchester Constructional Steelwork 15 www.bdonline.co.uk Association and Tata Steel p ho t o: n ic k a e p ho t o: d esig n e gi

portico A 12m-high galvanised-steel frame creates a suitably impressive portico. Steelwork contractor Snashall Steel created two 850mm-wide and 200mm-thick corner fins using steel “ladders” clad in powder-coated aluminium panels. These are of different heights to accommodate the sloping site. “The architect wanted to see fins, so we used a double column arrangement to support the weight of the artwork structure,” says Heyne Tillett Steel project engineer Andrew Blasdale. “The ladder arrangement gives fixing positions to the cladding and provides nominal interconnecting restraint to the two columns in their weaker direction.” The frame contains an oculus — originally intended to be positioned above a reflecting pool — which throws a circle of light onto the ground and backlights the artwork. Due to the cost and programme constraints on the project, Snashall Steel decided to use four corner beams at 45 degrees to provide an octagon. This was then finished off with plywood to create the curve. i m age : He yn e T ll et S tee l p ho t o: n ic k a e

pedestrian flow through to the lated rainscreen cladding and broken so that students don’t feel tles, denoted by suspended steel Clockwise green space alongside, known as blockwork walls. The 12m-span as if they are imprisoned inside. boxes, with the exception of a rust- from main the Dytch, Jobson adds. precast concrete planks provide “It’s a repetitive pattern that you ing weathering steel element that image: 4 Another important factor was thermal mass and use integral break with an alternative pattern represents Judas. These are linked The portico the nature of the adjacent St Ed- water pipes as part of an active that also repeats. It has a rigour by 30 polished rods in reference artwork uses burga building, which has floor- cooling and heating strategy. but also a certain account of free- to the 30 pieces of silver that was suspended Thirty pieces to-ceiling heights of just 2.3m. On the south side of the build- dom,” he adds. the price of Judas’ betrayal. Two steel boxes 3 Ideally, the architects would ing, the recessed elevation is over- The glazed link between the St Douglas fir timbers form a cross. to represent 2 have wanted to provide level floor hung by a 1.5m-wide colonnade Alphege and St Edburga build- Other elements include thin verti- the apostles; 8 Two layers of 1 5 plates to ease the transition be- of large brise-soleil blades. The ings contains the main entrance cal strips of larch, which symbol- tween the two buildings, but this and is dominated by a purple ise the population of the college. larch brise- 6 was problematic because of the “scissor” steel staircase which The architects have made the soleil help to desire to provide higher teaching ‘My worry was leads to teaching floors, as well as most of views through the build- animate the of silver 7 spaces in the new accommoda- that a teaching a mezzanine with computer and ing, with a full-height window side elevation; tion. The practice therefore opted desk space. opening onto the portico from the Structural Design Engine’s new teaching block for the University of Winchester is to make the ground floor of teach- building wouldn’t The staircase is cantilevered lower teaching level, and visual steel model. ing studios double height (4.5m) have a frontage 5m from the edge beams on each connections through the linking dominated by a steel-and-timber portico inspired by Christian symbols site plan so that the first floor could align landing, with hollow section building to a new rear courtyard. with the new upper storey of St with some stringers further stiffened by a The new building is designed Text by Pamela Buxton 1 St Alphege building 2 Link building 3 St Edburga building Edburga. welded steel plate balustrade. to achieve a Breeam rating of 4 University Centre 5 Piazza 6 Theatre 7 Dytch 8 Library Steel was the only viable op- element of This solution avoids the intru- “Excellent”. The entire project, tion for the primary structure, closure to what sion of support structure into the including the adjacent building’s rooftop extension according to engineer Heyne Til- circulation space. Instead, each steel-framed upper floor, cost a One of the trickiest aspects of the project ith its 12m-high then the University of Winchester ing space, the university decided for the building to create a suit- lett Steel, because of the intense would be an half landing is supported only by total of just £3.8 million at a rate was creating the lightweight steel-framed steel portico and dis- in 2005. to redevelop an inadequate 1920s ably impressive presence on the time pressure to complete the St the staircases going up and down of £2,150 per sq m. “There’s a lot of storey on top of the St Edburga building. tinctive Christian- Design Engine has worked ex- arts block in front of the library new piazza, which has become an 6 Alphege building before the 2012 important public from it. The curved staircase has a building, and a lot of complexity,” Although the skeleton portal frame was inspired artwork, tensively on the campus, which to provide eight flexible teach- important outside social space on 2 autumn term (the St Edburga space’ randomised pattern of circles cut says Jobson. fairly standard, the challenge was getting 1 4 there’s no missing occupies a steeply sloping site on ing rooms for up to 600 students. the campus. 3 5 phase completed early this year). into the plate balustrade. the setting out right because the base Wthe University of Winchester’s the outskirts of the city. The St Design Engine’s eventual solution “My worry was that a teaching As a result, the programme was But it’s the portico that steals building wasn’t quite square, according new Learning and Teaching Alphege building, which was of- also creates a linking block to the building wouldn’t have a front- accelerated, with the design de- colonnade’s eight steel columns the show. This provides a frame PROJECT TEAM to Snashall Steel technical director Blair Building. ficially opened in January, helps to adjacent 1970s St Edburga build- age with some element of closure tailed and procured at speed in are syncopated with alternate for the artwork, designed by the Client University of Winchester Thomas. “The whole thing sat on top of Designed by local practice De- form a new public space bounded ing, which has been reclad and to what would be an important order to finish in time. In total, wide and narrow gaps; these are architects in consultation with Architect Design Engine the existing structure and fixed into the sign Engine, the St Alphege build- by the University Centre — com- given a lightweight, steel-framed public space,” says Design Engine steelwork contractor Snashall balanced with a pattern of timber vice-chancellor Professor Joy Main contractor masonry,” he says, adding that this was ing is the latest facility to be added pleted by the practice in 2007 — rooftop extension containing two director Richard Jobson. “So Steel Fabrications Co supplied slats that the architects derived Carter. She wanted a piece that Geoffrey Osborne achieved using chemical anchors. to the former King Alfred teaching and the theatre, which the practice further teaching studios. we developed the idea of a large site section 300 tonnes of steel. from an overlapping “golden would reinforce the relationship Structural engineer The existing roof finishes and toppings college’s campus, following its re- refurbished in 2003. As well as providing the ac- oversailing roof with an oppor- The building is constructed rectangle” proportioning system. of the university with its Christian Heyne Tillett Steel were removed and the original brick piers incarnation as first University Faced with an urgent need for commodation the university re- tunity for an artwork.” The gran- 1 Library 2 St Alphege building 3 Double-height first floor with a steel superstructure with Rather than running continu- heritage. The work represents Steelwork contractor were tied into the new steel columns. 4 Link building 5 St Edburga building 6 Rooftop extension College Winchester in 2004 and improved and additional teach- quired, the architects were keen diose steel atrium also facilitates composite beams, highly insu- ously, says Jobson, the pattern is Christ surrounded by the apos- Snashall Steel Fabrications Co Friday 26/07/2013 In association with The British Friday 26/07/2013 www.bdonline.co.uk 16 STEEL FOCUS cost analysis Constructional Steelwork 17 www.bdonline.co.uk Association and Tata Steel

indicative cost ranges breakdown of frame costs

TYPE GIFA rate (£) GIFA rate (£) BCIS index 100

Frame: low-rise, short spans, repetitive 75-100/m2 90-120/m2 Raw materials: Putting grid/sections, easy access (see Building 1) 30-40% Frame: high-rise, long spans, easy access, 125-150/m2 140-170/m2 Fabrication: repetitive grid (see Building 2) 30-40%

Frame: high-rise, long spans, complex 145-170/m2 165-190/m2 Construction: access, irregular grid, complex elements 10-15% Floor: metal decking and lightweight 40-58/m2 45-65/m2 frames concrete topping Fire protection: 10-15% Floor: precast concrete composite floor 45-60/m2 50-70/m2 Engineering: and topping 2% Fire protection (60-minute resistance) 7-14/m2 8-16/m2 Transport: Portal frames: low eaves (6-8m) 45-65/m2 55-75/m2 1% on a firm Portal frames: high eaves (10-13m) 55-75/m2 65-90/m2

■ High-rise and longer span the structural works would have Separate cost allowances are repetition and connection type as buildings, typically 10-15 sto- commenced in the first quarter made for preparation and coat- these can significantly impact on reys plus basements. These of- of 2013. After this point, there ing works, fittings and fire pro- frame costs. ten require longer structural grid should be allowance for inflation. tection. footing spans, increasing frame weight, As the pie chart above shows, Case studies and may require cellular beams During detailed design raw materials make up only 30- The costs for the two typical office for the distribution of services. As the design develops, a more 40% of total frame costs, with fab- buildings below were developed Use of regular column grids may detailed costing of the structural rication the same again, followed by G&T, Peter Brett Associates Accurate costing from the be hampered by irregular city- steel frame on a per tonne basis by construction, fire protection, and Mace Group and updated centre sites or the requirements can be made. This requires draw- engineering and transport. As a quarterly. Embodied carbon was outset is essential to choosing of mixed-use schemes. This con- ings from the structural engineer rule, 20 hours of fabrication time discussed in the last Steel Focus tributes to higher average weights on frame configuration, cores is roughly equivalent in cost to 1 (3 May 2013). the right structural frame of steel frames of 65-85kg/m2 in- and shear walls, columns and tonne of raw material. For further information go to Text by Pamela Buxton Illustration by Nick Lowndes cluding fittings. Buildings over 15 beams, section sizes and types, With construction typically www.steelconstruction.info/ Ar tists ’ i mpre ssi on b y Ma ke c h it e cts storeys are likely to have a higher floor construction details and accounting for 10-15%, it is Cost_comparison_study proportion of complex elements the strategy or integration of me- worth considering the extent of Case Study 1 : Typical city-centre office building and non-standard sections, and chanical and electrical services. n a recent industry survey two frame and associated elements, the rate range can be 15-20% The nature of the main mem- thirds of architects identified since it can be costly and difficult higher than the top of the stand- bers, secondary members, fit- Case study 2: city-centre office building cost as the main driver in the to change the frame choice at a ard range. tings and connections should all choice of structural framing later date. Costs include allowances for be considered. Each structural material, with under a quarter “Otherwise, it may lead to a concrete costs and have been product, whether rolled I-sec- Ifeeling that steel frames were ex- project proceeding with a design developed from cost models of tion, structural hollow sections, pensive. solution that is not optimised.” the building types. For both, the fabricated plate girders or trusses But as steel frames have ac- average weight of the structural will have its own costs depending counted for 70% of all non- Recent cost trends frame is given. Within this range, on the differing fabrication and domestic framed multi-storey According to the Department for it is important to confirm antici- erection requirements. As popu- buildings over the last 10 years, Business, Innovation and Skills pated frame weights, variables lar sections may be manufactured this perception of steel is not (BIS), prices for both structural and fire protection with the de- up to four times more often than borne out in reality. So what can steel and steel reinforcement sign team, and also each key cost less common sections, it may be be done to ensure that costing is (and therefore concrete frame) driver in turn. less costly to use heavier options accurate both at the early stages fell steeply from the second half To use the table above, choose that are more readily available. of the design process when the of 2008 due to over capacity after the frame type that most closely To calculate the costs of the frame is chosen, and during de- the fall in demand caused by the relates to the project, add the floor structural frames, each of the tailed design stages? economic crisis. They then con- type and fire protection required different components will have a According to Gardiner & tinued to fall during 2009 before and adjust the total GIFA rate us- rate per tonne applied and then Theobald (G&T), which is car- generally stabilising from the end ing the BCIS index. These rates totalled. This will include all el- rying out ongoing research into of that year until the present (see can be considered suitable for ements of the cost of the profile i m ag e: a ke r c h it e cts constructional steelwork prices, chart below). Output fell by al- cost planning of projects where from raw material to erection. This is an eight-storey city- beams and slab with in-situ accurate costing can be challeng- most 35% by early 2010 compared centre office with a GIFA of columns. The overall floor- ing to achieve unless project-spe- with March 2008. than December 2011, this was those doing the costing should structural solutions, irregular procurement routes are increas- about 16,500m2. The design to-floor height for the steel cific cost drivers are understood. G&T’s analysis of steel frame generally not reflected in tender speak to the supply chain to find grids and the inclusion of non- ingly common compared to Case Study 1: business park office building is L-shaped with a central option is 4.18m, and 4.375m “Decisions on frame material tender prices over the last five prices for fabricated structural out the reality of current steel standard sections will increase the previously dominant two- core, internal secondary for the concrete option. All choice and configuration are often years shows an initial fall in rates steel. With small rises in the cost costs. When given a typical cost overall frame rates due to higher stage approach. This generally This is a low-rise building in the concrete slab construction escape stair and double- costs are at Q2 2013 prices, made early in the design process in 2008 and 2009, with stabil- of raw materials in 2013, some range for different frame types, fabrication costs and more com- leads to more competitive tender an out-of-town location, with a of the lower floors. Floor-to- height reception. The clear based on the City of London. without the benefit of fully de- ity returning by the end of 2011 firming of the price of fabricated G&T suggests that, rather than plex connection details. prices. GIFA of about 3,200m2. It has floor heights for steel options floor-to-ceiling height is The steel composite option veloped information,” says G&T and continuing through to 2013. structural steel is also expected in using the highest rate of a range, it ■ Location, logistics and access an 18m-wide, rectangular floor include an 80mm service zone 3m, with a structural grid of costs more than 3% less associate Rachel Oldham. “None- However, in the six months after the second half of the year. is best to instead interrogate and Costs should be adjusted ac- Current costs plate and a floor-to-ceiling below the metal deck and a 7.5m x 15m. Curtain walling than the concrete option theless, it is important to review July 2012, the material price of understand what those rates buy, cording to geographic location. G&T has compiled current costs height of 2.8m. There is one 600mm service zone beneath is in 1.5m-wide, storey- on a whole building basis alternative solutions and the im- fabricated structural steel fell by Getting the price right and also how the standard rates Indices from building cost in- for two key building types: central core and two lifts. The the concrete slab. height panels with solar and more than 8% less in plications of project and site-spe- about 1.2%. While steel prices in To get an accurate picture of cur- can be adapted to suit project- formation provider BCIS cur- ■ Low-rise and short-span build- envelope has a brick outer skin Costs are at Q2 2013 prices control fins. Solid areas are terms of frame and floor. The cific factors on the design of the December 2012 were 2.7% lower rent pricing, G&T advises that specific needs. rently show City of London at 120 ings, typically two to four storeys and the window allowance is based on the City of London, lined with cold-rolled metal steel option’s lower floor- Those analysing costs need to with the lowest at 66 (see with a regular structural grid of 35% of the facade. Ventilation and exclude fees, VAT, project studwork, insulation and to-floor height reduces the Prices of common structural materials 2008-13 consider the key cost drivers that below). 6-9m for largely column-free is mixed mode. contingency and fixtures. plasterboard. There is four- envelope cost by about 5%. impact on structural steel frames: ■ Site-specific factors are also space and floor-to-floor heights Peter Brett Associates The steel composite option pipe fan-coil air-conditioning Substructure costs are also ■ Function, sector and build- set a structural grid of 7.5m has the lowest cost in terms of and no natural ventilation. less, due to a lighter frame 200 important — for example, city- of 3.75-4m. Average steel frame ing height Average steel frame centre sites can be restricted weight is about 50-60kg/m2 x 9m for four frame types: frame and upper floors, and in The study compares weight and a lower roof cost. weights will vary considerably in terms of working hours and including fittings. Due to steel composite beams and total. The reinforced concrete two structural systems: a Mace estimates that both between different building types. deliveries, which can affect pro- the low-rise nature of the build- composite slab; steel frame option has the highest frame, steel frame with cellular options would require 20 An industrial building, for exam- gramme costs. ing, fire protection of 30-60 and precast concrete slabs; upper floor and overall costs, composite beams and weeks for substructure and ple, could have a frame weight of ■ Programme, risk, and pro- minutes would be considered reinforced concrete flat slab; with the frame and floors composite slab and ground slab construction. 150 40kg/m2 GIFA (gross internal curement route Single-stage standard. and in-situ concrete frame over 10% higher than the 60-minute fire resistance; For the frame and floor, the floor area) compared with 90kg/m2 with post-tensioned slab. steel composite option, and and a concrete option steel option would take 16 GIFA for a long-spanning city- BCIS location factors* For all options, the total building costs about 6% using post-tensioned band weeks, and the concrete 28. centre office building due to the foundations are unreinforced higher. The post-tensioned Building 1 cost model (per m2 GIFA) 2005 = 100 shed supporting a much lower Location BCIS index Location BCIS index mass concrete pads. Core option has a slightly lower Building 2 cost model (per m2 GIFA) load compared to the office frame. construction is steel cross- frame and floor cost than the TYPE Steel Steel and Reinforced Post-tensioned 100 City of London 120 93 Variations in floor-to-floor height braced framing with blockwork steel and precast option, but composite precast concrete flat concrete flat TYPE Steel cellular Post-tensioned concrete also need to be accommodated in Nottingham 93 Newcastle 89 infill for the steel options, the latter costs less overall concrete slabs slab slab composite band beam and slab Concrete Fabricated Precast Cement Concrete a cost matrix. Discussion of de- and concrete shear walls due to lower roof costs and reinforcing bars structural steel concrete 100 108 Substructure £52 £55 £67 £62 Substructure £56 £60 sign principles with the engineer for the concrete. For the a shorter programme. On Frame and and architect is essential to clarify 96 Belfast 66 roof, the steel frames have a average, both steel options £140 £151 £153 £150 Frame and upper floors £194 £210 upper floors 50 this. 92 98 lightweight steel deck and the can be built 5% faster than the Total building £1,861 £1,922 ■ Form, site conditions and com- concrete structures continue concrete alternatives. Total building £1,535 £1,561 £1,628 £1,610 * As at 13 June 2013 plexity of structure Complex MAR 08 SEP 08 MAR 09 SEP 09 MAR 10 SEP 10 MAR 11 SEP 11 MAR 12 SEP 12 MAR 13