THE ARUP JOURNAL WINTER 1991/92 Front cover: Kwun Tong Bypass. Hong Kong. under construction (Photo: L. M. Lui) THEARUP Back cover: Clerestory detail , National Gallery Sainsbury Wing JOURNAL (Photo: Peter Mackinven) Vol.26 No.4 Editor Winter 1991/92 David J. Brown Art Editor: Desmond Wyeth FCSD Published by Deputy Editor: Ove Arup Partnership Helene Murphy 13 Fitzroy Street, Editorial Assistant London Wt P 690 Joanne Worrall 3 Kwun Tong Bypass, Ove Arup & Partners Hong Kong designed the structure. including Hong Kong foundations. columns. and precast segmental deck. for 3.7km of Klaus Falbe-Hansen elevated highway on the Kwun Tong waterfront, alongside Kai Tak airport in Kowloon Bay. 8 Soda ash project, Ove Arup were responsible for the civil, structural, building, Sua Pan, Botswana foundation, and infrastructure engineering of this new plant to Colin Dittmer, Ernie Hall recover industrial soda ash from a 150km2 wellfield in a remote corner of Southern Africa. 12 Communications and This survey of work by Arups' Communications and IT Group Information technology includes communications infrastructures for the Department of Education and Science head office; the new Toyota plant; Hewlett­ Packard at Bracknell; Cellnet, Slough; and Hambros Bank; as well as a study for London Fire Brigade. 16 Welbeck: Arup Economics & Planning examined the economic and financial economics and finance viability of two alternative proposals for reclaiming 325ha of Jim Nyhan, Jonathan Mitchell despoiled land in West Yorkshire, by landforming with colliery spoil and waste from local sources. 17 Fabric engineering: This new office block at London Wall 1n the City of London The Lee House experience allowed a team of Arup engineers to develop a 'fabric John Pilkington, Neil Noble, engineering' service for the architect, integrating the wide range of and David Anderson technologies available for use on building envelope elements into an overall design approach. 20 The National Gallery Ove Arup & Partners undertook the structure and services design Sainsbury Wing for the new building in Trafalgar Square. This article concentrates David Brunt, Alan Pepper on the rigorous environmental systems developed for the safe display and storage of some 240 early Renaissance paintings in a variety of media. 2 Introduction Kwun Tong Bypass, Kwun Tong Bypass is part of Route 6, the 18km Government's original plan, which put great high speed link between Hong Kong Island. pressure on completing the rest of the link. Hong Kong Kowloon, and Sha Tin in the New Territories. Phase II is a 2.3km dual three-lane viaduct. The 4.8km Bypass connects two tunnels: partly over water. with four elevated ramps Klaus Falbe-Hansen Eastern Harbour Tunnel between the Island and totalling 0.9km in length. Phase Ill is 1.4km long Kowloon, and the Tate's Cairn Tunnel to Sha Tin. with one 0.2km long ramp . Dragages et Travaux It was contractually split into three phases of Publics, a subsidiary of the French contractor which only II and Ill were tendered com­ Bouygues, prequalified in September 1988 in a petitively, Phase I being completed as entrusted 90/10 Joint Venture with Bachy Soletanche to work by the Harbour Tunnel contractor, due to tender for both phases, and asked Ove Arup & early completion of the tunnel. This opened for Partners Hong Kong to assist them during the traffic in July 1989, 18 months ahead of the tender period. 2 Phase II Expressway Phase 111 Expressway Phase II Works Area Phase 111 Works Area 1000 metres ... New Seawall New KAI TAK Passenger AIRPORT Typhoon Shelter Ferry Pier Airport Runway Phase II tender design The 'conforming scheme' The erection technique envisaged in the con­ The alternative scheme The engineer for Phase II, Freeman Fox forming scheme utilized an underslung launch­ The alternative segmental scheme used two Maunsell (FFM), issued tender documents in ing girder for the precast segments of Section basic box types, a large one typically 12.?m October 1988. The tender period was six B. Although this method is efficient for the con­ wide with cantilevers for the carriageways, and weeks. In their 'conforming scheme' design, struction of long straight decks, it is not easily a small box typically 6.2m wide with cantilevers FFM had divided the viaduct into three sections: adaptable for strongly curved alignments. for the ramps. Where carriageways and ramps two geometrically complicated end sections A Dragages favoured the use of an overhead merged, the cross-section comprised large and and C. and a central, almost straight, section B. launching girder to erect the segments by the small boxes connected through 0.5m wide in parallel to Kai Tak runway and mainly over balanced-cantilever system; the girder could situ stitches between the cantilever slabs. The water. also be adapted to cope with the changing length of the box cantilevers varied according Sections A and C. with sharp, horizontal. 190m horizontal deck alignment. By pivoting it on two to the required overall deck width and the length radius curves and widening decks to accom­ sets of transverse running rails it would be of segments varied with span length. Limiting modate the slip-road bifurcations, were to be of possible to move it sideways and rotate it segment dimensions - in particular the max­ prestressed concrete, constructed in situ by the relative to the deck centre-line when placing a imum segment weight of 80 tonnes - were span-by-span method. The cross-section was a pair of segments. Based on this method, a fixed by Dragages so that it would be possible multi-cell box 25m-43m wide for the two precast segmental alternative design was to use, with only minor modifications, the carriageways, and a 6m-8m wide single-cell box developed for the entire viaduct. launching girder which had just successfully for the ramps; construction depth was 2.0m, completed the construction of the Viaduc de except for one ramp which clearance problems Sylans near Chamonix in France. reduced to 1.8m. Span lengths varied between The Phase II viaduct was divided into several 30m and 40m. independent expansion units, the length of Section 8 was to be in precast segments with which depended on earthquake design re­ match-cast epoxy-glued joints erected span-­ quirements and deck geometry. The longest by-span. The cross-section consisted of two were 240m, consisting of six 40m spans on the separate boxes. one for each carriageway. The straight central section B of the viaduct. At boxes were single-cell and 12 .Sm wide for most tender stage a detailed preliminary design was of Section B. but towards Section A where the carried out for one of these six-span units to deck widens to 2 x 1Sm. two-cell boxes were establish reliable and economical quantities per used. The construction depth was 2.25m and m2 of bridge deck for concrete, reinforcement the span length was 40m. and prestressing steel. The benchmark for The foundations consisted of 1.5m-1 .8m these quantities, with due consideration being diameter bored piles to bedrock, with pile given to the design standards of Hong Kong , lengths in the range 30m to 60m. was what Bouygues had been able to achieve for bridges erected in a similar way on design­ Comparing unit quantities in the three sections and-construct contracts in France. The quan­ of the conforming scheme showed a lack of effi­ tities found for the six-span unit were extra­ ciency in Sections A and C when compared with 2 polated and applied to all the remaining expan­ the precast Section B, where quantities per m sion units to provide quantities of principal deck were about 30% less. It was therefore materials tor the complete viaduct. clear that an alternative design extending the 3. Launching girder near junction In the conforming scheme. all bridge bearings use of the precast segmental construction of Phases II and Ill. January 1990. would be economically attractive. were of the mechanical pot type. The Arup 3 design used the more economical elastomeric bored piles. Our Phase II quantities for precast Dunng each of the (normally four) cantilevering bearings wherever possible, and pot beanngs segmental construction were extrapolated and stages, temporary Dywidag bars hold the last only where earthquake restraint was required or used for the Phase Ill deck. The savings in quan­ pair of segments in position until the epoxy glue where the vertical load exceeded 10 OOOkN. tities relative to the conforming scheme were has set. Then the permanent top cables are Only minor changes were made to the column again substantial: concrete reduced by 20%, installed and stressed, and the next palf of shapes during the tender phase. but the design reinforcement by 50% and prestressing steel by segments can be attached. The permanent resulted in reduced reinforcement quantities. 30%. However, there was one major obstacle cables were, in the alternative scheme. Arups carried out an alternative foundation to the alternative system and that was the lack anchored in the end face of the segments with design for the whole viaduct based on the of a works area for a precasting yard. Only 11 the 1nstallat1on and stressing of the cables reduced self-weight of the alternative deck. For Phases II and Ill were combined, and the works carried out from a platform supported by the the land-based pile caps barrettes were used, area set aside for Phase II became available. launching girder; in a three-day cycle this opera­ typically 1.0m x 2.8m in cross section, instead would a precast segmental solution be feasible tion became critical, and the contractor decided of the bored piles. A barrette - a rectangular for Phase Ill.