3 Ngong Ping 360 John Batchelor, Suresh Tank 15 Waste as ... - Arup

27. Arup assessed materials for glazing the cable car cabins.
Risk assessment
Tower 7
46m
483.0m
MTRCL also appointed Arup to assess the
preferred materials for glazing the cable car cabins
(Fig 27). These included polymethyl methacrylate
(PMMA), polyethylene tetrephthalate copolymer
(PETG), and polycarbonate (PC). An assessment of
the implications of these products from the fire
hazard point of view was required for MTRCL to
come to a decision with the cabin manufacturers,
who preferred a more expensive material.
Arup’s fire hazard assessment of these glazing
materials included identification and assessing the
likelihood of potential ignition, fire scenarios during
operation, related combustion behaviour and hazard
levels, and a literature review of their use on similar
projects. Based on the risk assessment, MTRCL
was able to select the appropriate material that was
also acceptable to the cabin manufacturers.
Value engineering
During Stage 2, Arup and Maeda proposed several
value engineering initiatives. Once agreed with
MTRCL, these were implemented and factored into
the gainshare/painshare equation agreed between
MTRCL and Maeda.
At the Tung Chung terminal, the main structural
frames were altered to use edge cantilevers for
structural efficiency, and to resolve headroom
problems. The roof geometry was developed with
straight members and the elimination of purlins for
simplicity of fabrication, in spite of the complex
roof shape (Fig 29).
Foundation savings in the detailed design of the
piles were achieved, but the more radical alternative
of a raft instead of bored piles, which would have
saved around 20% of the building cost with
appropriate detailing, was not adopted due to
MTRCL’s concerns over the uncertain fill properties
in the area.
28. Computational evacuation software was used to address
the means of escape provision by calculating total
evacuation time. This showed the risk of exposure to
fire and smoke to be low, as the total evacuation time is
less than five minutes.
388m
Ngong Ping
terminal
29. Value engineering at Tung Chung terminal: the roof geometry was developed with straight
members and elimination of purlins for simplicity of fabrication, in spite of the complex shape.
As already noted, the application of Arup’s fire engineering skills resulted in the
deletion of a large drencher tank and system, whilst the foundation solutions for
the AIAS achieved reduced pile quantities following the critical review by Arup of
the piling design.
At the two angle stations, Arup achieved reduced steel roof weights of around
50% compared to the target cost figures by using more structurally efficient trussed
frames, which also simplified the lifting problems for those stations in the country
park areas. In addition, the minipile sizes were reduced and the excavations
minimized by raising the foundation levels, thus reducing the amount of material to
be disposed of by helicopter or mule.
At the Ngong Ping terminal and theme village, steel frames were generally
changed to concrete frames, and foundations reduced in size as well. Again at the
theme village, the stream diversion gabion layout was reduced to take advantage of
existing rock outcrops found during excavation. Taking into account the approvals
timing and design change costs, each works proposal was evaluated on its merits
and agreed with MTRCL before implementation within the target cost contract.
The benefits of the target cost approach were clear from the alignment of all
parties’ mutual interests towards seeking the most cost-effective solution overall for
the project, using planned and agreed redesign, with extra design costs, to yield
larger savings throughout construction.
The Arup Journal 1/2008 13
444.0m