awarded essays

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CHUA Shui Ying, Ariel

Large-span Structures by ArchSD Introduction It was recorded in the Bible that when God created the world, He ‘saw that it was good’. This sentiment remains today, as civil engineers and architects strive to make their creations more that just a shelter for man’s physical needs. It has become a pursuit of aethestics, a battle against technical challenges and a mission to construct for the wellbeing of the community. In the past 20 years, the Architectural Services Department (ArchSD) has studiously maintained such sentiments in its work, and one of the perfect manifestation is the numerous large-span structures that now stand proudly in every corner of Hong Kong. History of Large-Span Structures by ArchSD Large-span structures are mostly roofs for hall or hall-type buildings. As such, selection of a structural system that could cater to both technical feasibility as well as functional requirements of the facility becomes essential. In the context of an auditorium, for instance, supports of structure should not be placed in the audience area, yet the the span should be designed to be the minimum possible so as to limit the internal forces in structural members well as the construction cost. Under such design rationale, ArchSD began its quest in the 1980s to erect large-span structures across the territory in fulfillment of community needs for facilities. The collection comprises mostly sports grounds, swimming pools and large-scale sports complexes. The most outstanding has to be the Hong Kong Coliseum, which was one of the earlier large-span structures in Hong Kong, but also one of the biggest. As expertise in its design and construction grew, ArchSD began to replicate large-span structures in other types of construction other than sports facilities, as demonstrated by the emergence of the HK Museum of Coastal defence in 1999 and Hong Kong Film Archive in 2000. Structural Forms of Large-span Structures Most of these large-span strucutures are composed of structural steel in the form of a truss system. While these roof trusses has a load-transfer mechanism similar in principle, they all have their uniqueness, be it the use of a wave-like space frame in the Shing Mun Valley Swimming Pool, or the extra long span of 69.9m in the recently completed Ma On Shan Sports Centre.

Figure 1 Wave-like Roof of the Shing Mun Valley Swimming Pool

Where opportunity presented itself, the ArchSD also proudly took on the challenge of adopting alternative structural system. The Tsing Yi Municipal Services Building, for one, differentiates from its “peers” with its cabled-stayed roof system that transfers roof loads to four central masts through tension rods. To cope with their inability to take on compression loads, the cable-stayed system also consisted of a concrete slab and steel decking on top of the steel truss on one side to resist wind uplift.

Figure 2 Cable-stayed Roof Structure of the Tsing Yi Municipal Services Building

Materials in Large-span Structures While structural steel has its appeal in strength, the industry’s ample experience in handling it, and

Concrete Slab

with Steel Decking

Steel Mast Tension

Rod Roof Truss

relative environmental friendliness given its recyclability, creativity and innovation also came in with the use of non-structural steel materials. An example which earned much accolades is the Museum of Coastal Defence, which has a tensioned fabric roof structure. This proves to be a perfect choice for such a facility as it allows some penetration of sunlight, creating an ambience of openness and saving electricity, but not so much as to lose its function of providing shade to visitors. Situated at a high point of a hilly site, the fabric roof also has the major mission to combat wind uplift. This is assisted by an intricate anchorage structure, comprising tension cables, central masts, peripheral tripods and minipiles as the foundation system.

Figure 3 The Museum of Coastal Defence

While some decisions were made with excellent acumen, some were less so. In the design of of Hammer Hill Road Sports Ground, reinforced concrete folded plates were used in the cantilever roof structure. Given its bulkiness, however, a solid concrete slab had to be used as counter-balance, and this added to the already heavy dead load and necessitated the use of large foundations. Though structurally sound, it was deemed not so environmental friendly in terms of the material and equipment needed in the process of construction. However, from the viewpoint of lesson learning, this would make an invaluable episode in the knowledge database.

Figure 4 Folded Plates used in the Hammer Hill Road Sports Ground

Safety Issues with Large-span Structures The pride of a large-span structure lies in its magnificent outlook and complexity in its design and construction. A major issue is always the safe installation of steel trusses. Where site conditions permitted, ArchSD has opted for alternative construction sequence to minimize the risk. This was demonstrated in the erection of the Hong Kong Coliseum, where the roof was assembled on the ground and lifted in position by four hydraulic jacks. This method removed the need of truss assembly at height and thus the risk of fall, while also putting forth the bonus of being environmental friendly as it required no scaffolding and working platforms. Where lifting and assembly at height of steels trusses were inevitable, ArchSD has also formulated measures to ensure maximum safety. This included the stipulation of a comprehensive lifting plan and risk assessment, of briefing sessions on lifting operation and tool-box talks on relevant safety aspects. Upon project completion, there were also post-construction evaluations to make sure the performance would be yet better when the need for another large-span structure came around. Conclusion It is not hard to figure out why large-span structure is a lure. The grandiose outlook elicits praise from even the layman, while the challenges and intricacies bring forth immense self-gratification in the ones who design and construct it. The major significance is that such grandeur or complexities are not consequences of overly big egos, but that of practical needs, which the Architectural Services Department has been tackling in the past twenty years with humbleness and diligence. It can certainly rest assured that citizens of Hong Kong would look upon their work and see that they are good.

Co-1st Runner-Up

TONG Man Man

Large-span Structures by Architectural Services Department

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Large-span Structures by Architectural Services Department By Tong Man Man To commemorate the 20th Anniversary of Architectural Services Department, a technical seminar and a technical visit were held on 23 August and 26 August respectively. These activities were organised by the Department, jointly with Building Division, Structural Division and Young Members Committee of the Hong Kong Institution of Engineers. In Hong Kong, all the public leisure and recreational facilities are procured by the Department. One common feature of these is the need to provide a large column free space by adopting large-span structures. The Department would like to deliver the attention on large-span structures to the public, together with professional engineers by sharing the extensive experience on these through these activities. Before the establishment of Architectural Services Department, Architectural Office has already dealt with large-span structures, such as Hong Kong Coliseum (Figure 1) where is a well known venue to hold international sport competitions and other recreational events. A large-scale steel space truss is adopted as the roof to create a large column free space.

Figure 1 Overall View of the Steel Truss

Large-span structure is increasingly receiving attention and appreciation from both the public and professional engineers. The Department has also widely chosen large-span structures in these recent projects, such as Ma On Shan Sports Centre (Figure 2). There is a dramatic large-span curved roof to form an 80m by 60m column free open space for the sport arena with unobstructed views from the spectators stand. The curved roof is elliptically shaped and symmetrical about the centrelines in plan. Two curved main steel trusses spanning 70m longitudinally provide the primary support for the roof system. The trusses are supported on

reinforced concrete columns through pin connections. Because of its structural elegance, this roof is accepted as a local landmark.

Figure 2 The Appearance of the Sports Centre

Structural steel is not only to form a space truss, but could also form a cable-strayed structure in constructing large-span structures. The cable-strayed supported roof of Tsing Yi Municipal Services Building (Figure 3) provides a positive contribution to the visual environment. The roof, hanged by a cable-strayed system, is composed of roof truss and concrete slab with steel decking.


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Steel mast and tension rod assembles the cable-strayed system. The wind uplift force on the roof is one of the critical considerations and is counterbalanced by the dead load, such that the tension rod would not experience any compressive force.

Figure 3 The Elevation View of the Roof

From the structural point of view, the bending moment would be significant when the span length increases. As lighter material is welcomed in practices, reinforced concrete is limited on this usage because of the greater dead load. However, in special circumstances, greater dead load is preferred, such as the roof of Hammer Hill Road Sports Playground (Figure 4). The roof of the stand is folded plate tapered at the end, while there is a solid concrete slab at the back span to increase the weight such that the bending moments

at the supporting columns could be diminished by balancing the load between two spans.

Figure 4 The Elevation View of the Roof

Besides to common construction materials, timber could also be used to construct large-span structure. Glued-laminated timber, made in New Zealand, is used in Aberdeen Sports Playground (Figure 5). The timber forms the rafter, purlin and main beam for the roof of the spectator stand. To deal with durability, the timber is adopted for resisting deterioration.

Figure 5 The Appearance of the Timber Roof

Figure 6 The Appearance of the Fabric Membrane Roof

In the choice of construction materials, there are numerous considerations, including construction method & safety, structural stability, environmental impact, architectural prestig and cost. Hong Kong Museum of Coastal Defence (Figure 6) is special in the choice of material; neither reinforced concrete nor structural steel was used for the large-span. Fabric membrane roof spanning 42 meters creates a vast central courtyard.


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This is the first enclosed fabric structure in Hong Kong and the membrane is prestressed with tension cables. The closure flap, made of PVC, is a coated polyester fabric reinforced by intermediate fibreglass strip. The merit of fabric is an environmental friendly material as the PTFE coated fibreglass is translucent allowing natural lighting. Designing the large-span structures, the choice of construction materials is important. Moreover, a more challenging aspect is construction safety as the construction often involves lifting procedure. As a result, safety aspect should be carefully supervised. The stability after completion is important, and the stability of partially completed structural component is also one of the critical stages, such that the construction sequence should be assessed to identify accident risks. In addition, operation and maintenance of the structures should be taken into account in the risk assessment. Environmental impact is increasingly regarded as an important issue in the public. The environmental friendly structures should be achieved as far as possible, such as implementing conservation of energy by using translucent fabric and reducing the consumption of natural resources by choosing recyclable materials. Through these activities for celebrating 20th anniversary of Architectural Services Department, the public could appreciate and understand the design and construction of long-span structures for public amenity buildings in Hong Kong. We are looking forward to having more long-span structures as landmarks in the future.

Co-1st Runner-Up

WU Man Kin, Ken

20th Anniversary Celebration Mr. M. K. Wu, KenEssay Competition

Large− Span Structure by ArchSD

Being the works agent for Government facilities development in the past twodecades, Architectural Services Department ( ArchSD ) has been providingprofessional service to HK focusing on design, construction and maintenance forpublic facilities. Meanwhile, the aim of ArchSD in contributing to the building of abetter working and living environment for the people of HKSAR has never beenchanged. Among the countless magnificent buildings designed by ArchSD, quite anumber of these are renowned for their peculiar features. One of the common feature isthe Large- Span requirement. The design and construction of large- span structure infact took place through out the history of ArchSD. Some of these were introduced inthe technical seminar and the site visit organised by ArchSD in August 2006.

Hong Kong Coliseum was designed andconstructed by Architectural Office ( theforerunner of ArchSD ) in 1982. It provides thecity with a well designed and equipped multi-purpose indoor stadium where diversifiedactivities can be staged. The roof truss of the

coliseum spans 90 meters in both latitudinaland longitudinal directions, providingunderneath space for 12,500 seats and anarena of 41m x 41m. The roof truss wasassembled on the ground for the ease offabrication before jacking up to the top of thefour towers. This was one of the prominentprojects at that time.

Hong Kong Museum of CoastalDefense is located at the hillside ofLei Yue Mun Pass. Formerly knownas the Lei Yue Mun Fort, it was builtby the British forces more than ahundred years ago to defend theeastern approach of the harbour.ArchSD refurbished the fort into thepresent tremendous museum in 1999.The main exhibition gallery was covered up by a 42 meters diameter span fabric roof.The supporting tension structure consists of the central ring, valley cables, ridge cables,tie-down cables, main masts, perimeter masts and ground anchorages. The fabricstructure has an irregular plan shape to follow the air-raid shelters underneath. PTFEcoated membrane material is used as roofing for its lightweight and high tensilestrength.

Fig. 1 Hong Kong Coliseum

Fig. 2 Construction of roof truss of Hong KongColiseum, 1982

Fig. 3 Hong Kong Museum of Coastal Defense


This splendid architectural design project was awarded the Hong Kong Institute ofArchitects Annual Awards 2001 Silver Medal.

Ma On Shan Sports Centre was builtin 2003 to meet the recreationaldemand of the rapid growingpopulation in Ma On Shan and toredress the existing deficiency inpublic facilities in the district. ArchSDalso aimed at providing communityfacilities as a focal point for the local residents. Since the original centre was designed

to house a tennis court together with spectatorseats, a handball court, 2 basket ball courts, 2volleyball courts and 8 badminton courts, aparticular large main game arena of 63m x37m was required. The steel roof above thegame arena is elliptical in shape and issupported by longitudinal curved trusses withsecondary trusses optimising the archingeffect. The main trusses which are in

rectangular sections of 2.5 m wide x 5 mdeep span 69.9 meters longitudinallyand supported by reinforced concretecolumns through pin connections. Theywere fabricated off-site in Guangzhouand were assembled temporarily intotwo halves on site before erection tofacilitate transportation. The sport centerwas completed and opened to public inOctober 2004.

There are many other large- span structures design and constructed by ArchSD. Forinstance, Kowloon Bay Sports Ground, Choi Hung Road Playground, Hammer HillRoad Sports Ground, Spectator Stand at Aberdeen Sports Ground, Tsing Yi SportsGround, Siu Sai Wan Sports Ground, Hammer Hill Road Swimming Pool, Tsuen WanWest Sport Centre, Ma On Shan Swimming Pool, Tsing Yi Municipal Services

Fig. 6 Ma On Shan Sports Centre

Fig. 7 Main game arena of the sport centre

Fig. 4 Before refurbishment Fig. 5 After refurbishment

Fig. 8 Construction of the main truss, 2003


Building, Shing Mun Valley Swimming Pool and Hong Kong Film Archive. Large-span structures in fact are not something distant but living between each of us.Nevertheless, one may ask how to classify a structural span as large. I believe everysingle one would have his/her own interpretation.As suggested by the Chief Structural Engineer ofArchSD, Ir. M. K. Tong, as a structural engineer, weshould always treat every span as if it was a large-span. We should always try our every effort andenthusiasm in our design work. This innovative

concept meansa lot to theengineers ofnew generation. Not only to large- span structuraldesign that we should need to ensure thorough andcareful considerations have been given to find thebest structural solutions, but also we should proudof every bits of our own work. As a youngengineer, we should always try hard to take anactive part in the design team. Large- Span

Structure definitely would become larger in the future design, this would be achallenge for structural engineer, but also this would be a chance to steel us up. As theold adage states "Chance favors the prepared mind", have you got a prepared mind?

Fig. 9 Hammer Hill Road Swimming Pool, 1996

Fig. 10 Siu Sai Wan Sports Ground, 1996

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