Harry Giles, MSc (Eng) MIStructE Ceng

Exterior shot of ExCel conference centre side elevation fronting the River Thames at the Isle of Dogs, . The side eleva- tion of the ExCel conference centre shows the dramatic steel- work structure which forms the main architectural feature of the building. (Photo by Mandy Reynolds)

Modern Steel /August 2001 xCel, London’s new con- ference, exhibition and special events venue, is a new Docklands landmark that rivals the Canary EWharf tower in terms of sheer scale, al- though not of height. Located on good transport links, ExCel is a major venue for trade shows and public exhibitions, part of an over- all master plan by English Partner- ships. The site extends across a reclaimed dock, building over water using marine piles. The total develop- ment area is 193,500m2 ( 2,082,820 sq. ft.) gross, including 65,000m2 (699,650 sq. ft.) of exhibition space. The remain- der comprises car parking, a confer- ence facility, public amenity spaces, cafés, restaurants, cloakrooms, central security and plant. A second phase is planned to in- clude additional developments for ho-

tels, shops, multi-story car parking and each with an 86.7m (284’) clear span ning east-west and leading from the a crèche. over a clear height of 10m (33’). The main entrance. Externally, the halls are The primary development of exhi- halls are subdivided by full height attached to breakout spaces for private bition and conference centre has suffi- movable partitions located along the functions and offices, extending for the cient flexibility to allow sub-division of lines of the roof trusses at 7.8m (26’) full length of the building along the the main halls to cater for the differing centres. The main halls are separated north and south elevations. demands of exhibitions. The two major by a 29m (95’) wide internal spine cen- exhibition halls are 375m (1,230’) long, tral access “street,” the Boulevard, run-

August 2001 / Modern Steel Construction The roof construction tractor, Sir Robert McAlpine, and steel- checked the effect of pre-cambering A key feature of ExCel is externally work subcontractor, Severfield Reeve, and fit up as well as the logistics for exposed steelwork, consisting of cou- to arrive at an elegant yet economical erection. Each truss weighed approxi- pled pairs of “A frame” masts and ties solution that could be constructed mately 35 tonnes, erected in one piece supporting primary trusses near their within the programme. Long lead spe- with four cranes lifting simultaneously. midspans across the exhibition halls at cialist fabrications were avoided, and The main roof structure was de- 23.4m (76.8’) intervals. The exposed “A complex connections were simplified signed to span under its own weight frames” and ties consist of pre-cam- to enable fabrication and erection, during construction, which represents bered tubular steel inclined masts and achieving the desired sophistication in approximately 25% of the total load on ties. Frame modules are located at the final solution. the roof. The mast and tie supports the 46.8m (26’) centres along the entire With tubular members intersecting imposed roof dead load as well as the length on both north and south sides, from a variety of angles in highly visi- live load. The imposed dead load in- forming the main architectural expres- ble locations, cost of nodes manufac- cludes four air-handling units located sion of the building. The entire steel ture was a key consideration. within the depth of the roof structure frame, fabricated with nearly 10,000 Severfield Reeve proposed manufac- and partition loads that hang from pur- tonnes of steelwork, was erected in ap- turing the members in tubular steel- pose-designed tracks. proximately four months. work, avoiding time-consuming One of the reasons for adopting this The main roof structure consists of tensioning during erection stages. The form of construction was the push to lattice trusses at 7.8m (26’) intervals, visual interplay between the struts, ties erect steelwork quickly. This involved supporting the deck, the main air-han- and node connections was carefully pre-erecting the steel superstructure dling plant and the hanging partitions considered. frame directly from foundations in ad- for the exhibitions below. The 67Kg/m2 The main struts are 762mm (30”) di- vance of the concrete deck and car (14 lbs. per sq. ft.) roof structure is an ameter circular hollow sections con- parking infill slab below. Rapid pre- exceedingly economic design, consid- nected to 356mm (14”) diameter erection of the main lattice trusses al- ering the large spans and the high im- circular hollow section ties, joined by lowed early completion of the posed service loads involved. 160mm (6.3”) diameter pins via fabri- envelope. Each truss was lifted in one The roof consists of a waterproof cated node connections. The tubular piece, exploiting the inherent stiffness membrane laid on insulation resting on hollow sections are tapered at their of the lattice trusses, spanning under profiled metal decking which spans be- ends, welded to connecting profiled its own weight together with signifi- tween purlins. The purlins span con- single and double fin plates to achieve cant pre-cambering of 500mm (19.7”) tinuously via a pre-assembled stub the elegance that resulted in the highly at centre span. The connections for the purlin connection on the top of each visible pinned connections. Care had to outer frame and ties followed the truss truss, connected prior to lifting it into be taken where the geometry resulted erection to enable completion together position. in longer than desirable fin plates to with the weather tight envelope, allow- Upper suspended floors within the avoid complications of movements in ing construction to continue below at breakout areas and central Boulevard the pin connections close to the water- the same time. are of conventional composite metal proof membrane. Articulated pins The manufacture of the main node decking, acting compositely with steel were kept external and clear of the connection between the columns, the framed beams via shear studs. membrane, and fin plates had to be truss and the “A frame” members was Running the entire width of the checked for buckling instability, plac- not without its limitations on the size building, two expansion joints ,create ing further limitation on options for the of fabrication. This was due to the need three individual sections along its visual elegance of the connection. to preheat the complex arrangement of length, thus subdividing the building These complications were resolved the plated assembly to satisfy welding structurally to allow for thermal ex- in discussions with the steel fabricator. procedures. The size of the pieces was pansion. Each of the three sections is Working closely with the architects, limited by the size of oven used to braced in two directions, providing the Buro Happold carried out various achieve the necessary amount of pre- necessary stability for each portion of studies, including model making and heat. The resultant configuration suc- the building. 3D visualisations. In this way, the team cessfully resolves all the demands arrived at a solution that was visually placed on this key connection, in an el- Features steelwork acceptable and achieved a buildable egant and cost-effective way. and connections and economic design. ExCel brings a new landmark exhi- The elegant exposed steelwork was bition facility to the heart of London. a significant design challenge and held Fabrication and erection The efforts by the entire design and fabrication challenges as well. Moxley A complete trial erection of a pri- construction team, with the support of Architects and Buro Happold Engi- mary truss and “A frame” module car- the client, have contributed towards a neers worked closely with main con- ried out at the fabrication works building of distinction to grace the ever- changing brownfield develop- ments in London’s Docklands area. Harry Giles, MSc (Eng) MIStructE Ceng, is a Senior Associate with Buro Hap- pold in Bath, England. CLIENT: ExCel

CONTRACTOR: Robert McAlpine, Hertfordshire, England

ARCHITECT: Moxley Architects, London, England

STRUCTURAL ENGINEER: Buro Happold, Bath, England

SOFTWARE: Interior shot showing large exhibition space. One of two major exhibition halls Strap lies at the centre of the building providing a 375m (1,230’) long and 86.7m (284’) clear span over a clear height of 10m. The space can be subdivided with full height movable partitions. (Photo by Mandy Reynolds).

Exterior shot of corner of building showing carpark rampways and entrance in background. The purpose built exhibition space allows for vehicle access straight into the exhibition halls. (Photo by Mandy Reynolds).