data.entry 10 | 09 | 2001
02 | 00 Archive
Building: Materials & Equipment Southeast Asia 1.03.1976
Cover story - 'The tallest apartment block in Southeast Asia, but within your reach'
This story appears with text 'as published' in 1976
Cylindrical tower provides high density accommodation in split-level apartments
In Accordance with the guidelines of Urban Renewal projects in Singapore, land parcels are made available on a public tender basis. In practically every case the successful bidder needs to be highly competitive in price and at the same time flexible in building design in order to warrant the best use of land.
It was under these circumstances that Pearlbank was conceived for a two acre hillside site beside Outram Park, which was zoned for residential development. The extraordinary design of Pearlbank consequently won not only the site for its developer but also several firsts in Singapore :
· The highest density for a residential development
· The tallest residential block
· The largest number of apartments contained in a single block
· Split-level apartments available on a large scale for a middle income group.
Designed for a population of some 1,500, the 38-story Pearlbank has a density of 750 (calculated by dividing the development's population with the site's acreage), while density is in the region of 400 for most other residential developments. The high density necessitated special treatment in the design stage. A point block would have provided only four to five units per floor and would have ended up in an absurdly tall structure. A slab block would have resulted in long, dark corridors.
A cylindrical building, which may be treated as a 'curved' slab block, provided the answer. The Pearlbank contains a total gross floor space of approximately 69,677 sq meters. The building is a 30.48m radius, 270-degree sector. The opening has been created to allow ventilation, view, fresh air, and natural light. The gap, facing west, has been oriented to avoid the sunset glare, as the bedrooms and living rooms are located on the outer rim. The inner void is approximately 30.48m in diameter.
The architects and developers also aimed to provide the maximum privacy possible for the apartments and to make available split-level living for the middle income bracket. The solution was then to adopt a three-frontage design for every apartment, combining the advantages of a point block with those of a semi-detached house. The result is a half-floor split, ranging from two to three levels per unit depending on its overall floor areas.
There are eight apartments per floor and the 'interlocking split' system puts all the bedrooms and living rooms in the front rim enjoying privacy, sunshine and natural light, and the service areas together with access staircases and a passage in the inner rim. It provides here the 'interlink' for what is meant to be isolated living units.
This layout allows apartments of three different sizes to be orderly arranged, in such a way that the pattern is repeated every three floors.
The apartments are relatively small since the aim is to accommodate a bigger population for the same quantum of space, a policy which also met with the Urban Renewal approval. The apartments are of three basic types : 130sq m, 176 sq m, and 213 sq m respectively (or 1400 sq ft, 1900 sq ft and 2300 sq ft) of two- three and four bedroom. They are provided in the ration of approximately 1:2:1 within the Pearlbank. In other words, the medium-sized unit of 176.5 sq m occupies most space. In addition, there are eight penthouses atop, each of 306.6 sq m (3,300 sq ft) plus a roof terrace of 92.9 sq m (1,000 sq ft). Altogether there are 296 units in Pearlbank. They were meant for sale to the middle income group and the economic feasibility study in 1970 put the prices at approximately $60,000 for a two-bedroom flat. Some two-thirds of the units were reportedly sold in those prices, which have since gone up with inflation over the years.
Careful planning ensures that in order to minimize disturbance, vehicular traffic will reach the carpark before the apartments. This is achieved by providing the vehicular entrance on Pearlbank and the exit on Outram Park. Since the Pearlbank development rests on a hillside slope with a drop of some 10.6 m (35 ft), and it is not economical to build a car park beneath the apartment tower, a separate, four-storey carpark has been built at the foothill using a ramp access. Carparks are provided in the ration of one per apartment.
The site which measures 7,943 sq m (85,500 sq ft) consists of hard decomposed shale with 12.2m (40 ft) of soft clay underneath, before reaching the bedrock some 24.4 m (80 ft) below. End-bearing in-situ bored piles ranging from 0.9 to 1.2 m (3 ft to 4 ft) diameter were used.
Structurally, the building is of reinforced in-situ concrete using slip-form construction for all shear walls. It is in fact one of the largest slipform jobs (apart from office buildings) performed in Singapore.
This design allows for 22.9 cm (9") thick party walls to be constructed, which contributes significantly to sound control and insulation. In fact, during the construction stage, the vertical elements went up so fast that the horizontal elements, notably the in-situ split floors and staircases, experienced a hard time trying to catch up.
According to Mr. Tan Chin Ming, general manager of Fabquip (S) Pte Ltd which undertook the slipforming job, the developer being the builder also saw the advantage of this method. At that time (arch 1972), Summit Hotel was the only non-office building to be slipformed.
The main feature was to achieve accuracy by having the initial set-up to the center point of building done near the bottom level; which progresses upwards without the necessity to refer to the center point of every floor. This is less time consuming and labour-saving as compared to the conventional method of building a 'kicker' for every floor to refer to the center point.
One difficult problem was the height (128.1m or 420 ft) and size of the eight independent lift shafts, which allowed only the minimum of plumb deviations - one inch at the maximum.
The initial design of the lift shafts was such that the corners are splayed (a safety factor because of circulation all round). However, it was found that the lift doors would not open completely and the tolerance was too tight. It was critical that it was suggested to the architects not to chamfer the internal wall of the shaft.
Keeping the above in mind, Fabquip had to counter check the plumb reading every 1.22 m (4 ft) by means of 10-kilo plumb-bobs on every wall.
Another feature to note is that the horizontal size and hence the distribution problem and the volume of concrete required per hour necessitated the subdivision of the structure into four sections, with each section having its own independent construction equipment.
Regarding the slab in two halves, Fabquip slipformed one floor of Stage 1 (see plan below) before moving on the same basis to Stages II, III and IV with the cycle repeated for each floor. The time of nine days per floor was attained for a typical floor of approximately 1,500 sq m.
For flexibility of movement, four hoists were used instead of one tower crane. It was also the most economical solution. Besides, the nearest power source for a crane available was at Chin Swee Road, 0.4km (a quarter mile) away.
The higher the form went, the longer the concrete pour for each floor took, as evidenced by the 12 hours taken for a higher floor against the eight hours for a lower floor.
Pneumatic form for refuse chutes
The refuse chutes were made by 'pneumatic form' as against asbestos pipe sections. This gave a much better finish as pneumatic blow sealed against the existing concrete wall.
Another disadvantage of asbestos pipe sections are their irregularity and higher percentage of breakage in the process of being hoisted to the upper floors.
The pneumatic tube system, of which Fabquip is the sole agent, was introduced for the first time in Singapore.
Free standing retaining wall
The car park is a four-storey structure, continuously ramping from the lowest to the highest level with a free standing 11.6 m high retaining wall on two adjacent sides. This wall was formed utilizing contiguous bored piles construction.
As high as Bukit Timah Hill
The brainchild of Mr. Chew Hin Suan, managing director of Hock Seng Enterprises (Pte) Ltd, its developer; the semi-cylindrical building - one of the most ambitious residential projects in the Republic - involved an investment far beyond $20 million, of which approximately $14 million was for the building cost.
The 113.4 m (372 ft) building now stands majestically atop Pearl's Hill which is 57.6 m (189 ft) above sea-level which makes it 117 m (561 ft). Singapore's highest peak, Bukit Timah Hill stands at 193 m (581 ft).
At one end of the building, an exterior staircase connects all floors, Another fire escape staircase is located internally, so that every apartment is within 21.3 m (70 ft) reach of the fire escape route, as required by government regulations. Another interesting feature of Pearlbank is the external service staircase units which protrude from the inner wall. These two-floor high staircase leads from the main door to the back door a floor below and is meant for use by domestic servants.
It also complies with government regulations that each flat must have at least two exits. The staircase units cantilever 4.75m (15 ft) from the floor. Construction of the staircases required special technique as they must be aligned toward the mid-air centre.
The building is served by eight 122mpm (400fpm) passenger lifts in eight evenly spaced lift cores, resulting in a private lift lobby for every unit. The lifts in fact stop at alternate floors because of the split-level design. There is a service lift and another passenger lift in the car park.
In case of power failure, three passenger lifts will be operated by emergency generators.
Lighting is by time-operated sunrise and sunset mechanism for public areas and others are manually operated.
The car park has all-night lighting, and the central park is lit partially after midnight.
The 1500KVA transformer room is situated next to the car park to provide three-phase power supply; individual electricity meters are installed. Electrical installation is by Lee Seng Kwang Electric (S) Pte Ltd.
Nam Fang Electrical Co (Pte) Ltd, the plumbing contractor provided eight centrifugal water pumps and four control panels.
The height of Pearlbank necessitated water to be pumped from the basement tank by 100hp pumps (one working and one standby) to intermediate tanks on the 27th floor and another set of 40hp pumps (also one working and one on standby) which in turn send the water up to the roof on the 38th floor.
Two booster pumps, of one horse power each, draw water from water tanks for the eight Penthouses. Distribution is by pressure to floors above the 26th floor, and by gravity to those floors below.
The plumbing system is duplicated on either side of the cylindrical tower. Although there are eight water tanks - teo on the ground, two on the 27th and two on the roof - supplied by Yong Tai Seng Engineering Works Pte Ltd.
William Jacks & Co (S) Sdn Bhd provided the Armitage Shanks sanitary fittings to all 38 floors.
Fire protection by Hart Engineering Pte Ltd consists of the basic wet and dry riser systems with hose reels and extinguishers at strategic points, and heat detectors.
A communal floor is provided on the 27th floor level for those staying on the lower floors have the chance of viewing the breath-taking sights. At a later stage, various recreational facilities are planned on this floor, which measures some 16.6 sq m (16,800 sq ft).
The first floor lift lobby and main entrance will later be developed to accommodate shops. Footbridges lead to the roof of the car park, where a pavilion designed for a kindergarten is also situated. Staircases link to the ground floor landscaped court, where brickwork screens shield off waste disposal points of rubbish chutes.
The temporary occupational licence was to be granted for the lower half of the tower at the time of writing. Meantime Brady's (S) Pte Ltd was putting the finishing touches to the specially designed ceilings of the penthouses. In the middle is a flat ceiling measuring 1.8m by 4.3m from which a step formation is moulded to follow the profile of the 'slant' on both sides. The step formation ends exactly at the window glazing.
To give an idea of the proportion of this fibrous plaster ceiling, the height from the floor to the ceiling is 3.2m (10.5 ft) and the height from the flat part of the ceiling to the end of the step formation is 2.28m (7.5 ft).
Externally, Pearlbank is finished in Shanghai plaster and the inner rim walls in Sandex matt (by William Jacks & Co (S) Sdn Bhd), accentuated by the brown two-story high staircases.
The corridors are finished in suspended ceilings which cover up service conduits and pipings. Internal finishes include parquet flooring, emulsion painted walls, up-to-ceiling tiling for bathrooms. Windows are provided with 0.61m (2 ft) ledges to prevent looking straight down, from a building reaching about the same altitude above sea-level as Singapore's highest peak, the 176.7m (581 ft) Bukit Timah Hill.
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