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

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9. Structural support at the AIAS for cable catenaries leading to Tower 3 and on to Nei Lak Shan angle station (NLSAS). Structure The top level of the AIAS reinforced concrete superstructure is a platform 25m above ground level (Fig 9), comprising two 40m long and 14m wide arms projecting from the central core at 120° relative to one another (Fig 10), each supported by a single row of reinforced concrete pillars down to bedrock. These arms support the structure for the separate systems of cables that serve the lengths from the Tung Chung terminal building and on towards the NLSAS. For each, a single row of reinforced concrete piers above platform level supports the main track and haul ropes and the associated cable car equipment and maintenance walkways. At the end of each platform arm, a single pier forms the main vertical support for the cable catenaries. 10. 120° angle between the AIAS arms leading to Tung Chung terminal building and to the NLSAS. The foundations are a combination of pad foundations on grade II/III rock for the columns that support the AIAS structure, and a raft foundation and pre-bored rock-socketed H-piles under the central core, providing overall stability under lateral loads. Rock joint mapping, boulder surveys, and slope stability assessment were carried out to justify the proposed foundation and rock slopes. The haul rope provides traction for the cable car system but does not support the weight of the cars themselves. It runs along either side of the central line of piers above the level 6 platform and is driven by a bull wheel on the pier closest to the central core. The bull wheel is connected by a drive shaft to a motor in the level 5 plantroom below. Two track ropes support the system’s vertical loads, one for each direction of travel. They are diverted from the main vertical support, down below the level 6 platform at an anchorage point within the level 5 plantrooms. The maximum design load on a single track rope, generated by the weight of the cable car system as well as other dynamic effects, is over 200 tonnes (2000kN of force). The combined effects of these loads from each side of the station, together with their 25m height above foundation level, generate the large overturning forces that in turn controlled the foundation design and stiffness of the superstructure. These permanent overturning forces are resisted by 500mm thick reinforced concrete core walls that spring from a stepped raft foundation, cast onto the cut rock slope and anchored by seven pre-bored rock-socketed H-piles. The ropeway designer produced a simplified envelope of design forces for each anchorage location for the civil works design, characterized by maximum and minimum loads for each location and loadcase type. Cable loads for dead, live and wind loadcases were provided for both an operational case, with a limited design wind speed of 135km/hr, and an out-of-operation case, subject to full typhoon wind loads. The loads were defined by moments and forces in all three global axis directions and resulted in over 100 design combinations that were themselves enveloped to complete the design of the foundations and superstructure. 312.6m Tower 3 17m The Arup Journal 1/2008 7
8 11. Nei Lak Shan angle station and Tower 4 slope reinstated after completion of stabilization works. 12. Geological model showing raking piles socketed in rock (blue) together with boreholes and structure above. The Arup Journal 1/2008 Nei Lak Shan angle station (NLSAS) General This building was sited on a rounded hilltop (Fig 11) with difficult access upslope from Tower 5 in Lantau North Country Park. It provides the turning point for the change of direction of the cable car towards Ngong Ping. As at AIAS, the cable cars detach from the rope and move at reduced speed along the station, so as to maintain riding comfort for the passengers before attaching back to the rope. The station comprises a lower ground level (basement) and a ground (platform) level. The roof superstructure is monopitch steel frames and roof finishes similar to that of AIAS, with concealed gutters and edge profiles. Foundations The foundations are simple pads and strip footings for the single-storey electrical and mechanical services buildings, and pilecaps and raking minipiles over the central structure supporting the cable car anchor drums and reinforced concrete columns. The minipiles were proposed due to the difficult site access (achieved by helicopters) and to minimize environmental impact. They rake in two directions (Fig 12) to resist the vertical and lateral loads - their orientation, number, and lengths being established after rigorous analysis that took into account several combinations of cable car loadings provided by the ropeway designer. 1063m A 3-D model of the ground conditions was created to assess whether any adverse geological features were present that could affect the size and shape of the rock and soil cones assumed in the tension capacity calculation, as well as the stability of any nearby slopes. The model was based on the findings of all previous and new ground investigations, as well as geological mapping and a desk study review of geological information of the area. The geological model did not identify any significant shearing or faulting running through the area of the foundations, and confirmed that no such adverse geological features would affect their overall stability or that of any adjacent slopes. It also confirmed the choice of socket length for each minipile under the structure. Structure Open cut staged excavations were undertaken to enable construction of the foundations, the excavation plans being prepared after discussion with the construction team, so as to suit the preferred construction method. Due to the site’s remoteness, every effort was made to minimize the volume of excavated material that had to be removed. The foundations for the single-storey E & M services buildings were raised, both to minimize the volume of excavation and limit bearing pressures to less than 100kPa. This was to avoid regulatory requirements for plate load tests, which would have been very expensive and difficult to carry out on this remote site. The top level of the NLSAS reinforced superstructure forms the platform. It is some 5.5m above the pilecap formation level, and comprises 40m and 35m long sections of platforms from the centre, at 160° relative to each other and supported by a single row of reinforced concrete pillars down to the pilecaps. These columns support the main track, the haul ropes, and the associated equipment for the cable car systems between the NLSAS and AIAS, and between the NLSAS and Ngong Ping terminal.
Page 1 and 2: 2 The Arup Journal 1/2008 Contents
Page 3 and 4: 4 Background Ngong Ping is an impor
Page 5: 6 7. Tung Chung terminal building a
Page 9 and 10: 10 The design of Tower 7 proved the
Page 11 and 12: 12 25. Detail of rescue trail timbe
Page 13: 30. Ngong Ping Village. Conclusion

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

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