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pressurised shaft

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air-conditioning room

Four test boreholes were conducted, to a depth of about 64 m for the sub-structure design Generally, these indicate the site to be underlain by successive layers of very soft to soft clay, followed by medium stiff to very stiff silt and silty sand Ground water table is between 2.7 m to 3.5 m below ground level.

Column loadings vary from 3.200 tonnes to 1,800 tonnes for the widely-spaced columns. For the more closely spaced columns, the loading is about 740 tonnes

In the selection of foundation for the structure, shallow foundation like pad footing and raft was considered to be obviously not suitable in view of poor soil (N-value of 3) to a depth of 9 m below ground level. Bored piling was not adopted in consideration of high water table with silty sand and low N-values at the upper layers. The requirements of long length of steel casings associated with boring in such soil to prevent collapse of bore holes would not merit value engineering decision

For such soil condition and medium range column loadings, it was considered appropriate to adopt driven reinforced concrete piles Further reasons to justify the use of driven r.c. piles are that they are economical (compared to steel piles) and could be installed relatively quickly. Piles used are as follows:

size 400 mm * 400 mm, with welded joint grade of concrete G45 driven length average 55 m working load 185 tonnes maximum no of piles/column 8 Essentially, these are skin friction piles which mobilise the good soil resistance properties at depth of 30 to 55 m

The idealised structure consists of moment resisting frames coupled to a shear wall. Horizontal and vertical r.c. members are rigidly connected together in a planar grid form which resists lateral wind loads primarily through the flexural stiffness of the members. This type of structural system is efficient to enhance the sway serviceability performance of the building. The structural analysis was carried out using the computer software STAAD-lll, with the appropriate gravity loads and wind loads, derived from a basic wind speed of 35.8m/s (80mph).

The maximum computed horizontal deflection of 98mm, is well within the deflection limit of H/500 (85m/500 = 170mm) The building was designed for conventional r c beam and slab construction which is economical for such medium height range. The quantity of concrete (G30) and steel reinforcement (Fy = 460 Mpa) used for the superstructure are as follows: Concrete 5,696 m^ Steel 1,195 tonnes To achieve an early hand over of the lift r.c. wall for lift installation, the contractor adopted the 'Jump Form" construction with a construction cycle time of 8 days for 3.9 m height of wall. With this method, the contractor completed the r.c wall construction 3 months ahead of the other areas which was constructed using normal steel and timber framework The entire project, including piling works, was completed in 22 months pilecap type P9 j pilecap type P11 pilecap typ« P16

structural & substructural engineering by Dr Gerry Wong

Tahir Wong Sdn Bhd (Civil / Structural Engineer)

section C-C

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Table 1

Scht<Jul* of s'mul.bom •or suck and wind (areas ol opening In brackets (m2)

Table 1

Scht<Jul* of s'mul.bom •or suck and wind (areas ol opening In brackets (m2)

Stage 1

^ ymutabons were earned out . < i c*" day with no wind and venblsbon driven ff* stack forces generated due to internal rtgcnx temperature deferences. . ---average wind conditions (2 5 m/s; south-^ffteriy) and I range of window opening conhgf hons

Table 2

Summary ol results

^ situations modeled a* shown m *ble 1 Table 2 summarises the mam results from the simulations For windows ^ doors ** open on the up-w,nd and down wind facades, vent.lat.on rates were very high for the wind condition corsidered Case 4 has only small openmgs (at X) and this has a more controllable ventilation rate of about 6 3ac/h Case 2 was repeated with a smaller area of window opening on the upwind doors. C (1.5 m1 instead of the fully open area of 4 2 m*) The again reduced the ventilation rate considerably

The results for the stack only condition. Case 1. are shown ,n figure 6 Figure 6 presents the internal temperature dntibubon and the air speed vectors at 1 2m height

Figure T presents the internal temperature distnbution and air speed vectors respectively for Case 2 (repeat)

Stage 2

Following these tests, further tests were performed for low (-1m/s at 10m height) and high (-5m/s at 10m height) wind spew n order to derive some guidance on window opening for the prevailing wind directions Results from stages 1 and 2 tit presented m table 3 and an approximate set of curves extrapolating from this data are presented in figure 8

A.8.D Location of widows on building

Table 3 «oris

• For ctadi effect only (i.e. calm conditions) the ventilation rate with all windows open is about 1 ac/h.

• At low wind speeds (1-1.5m/<) the ventilation rate Is about 4ac/h.

• At medium wind speeds (2.5m/s) the ventilabon rate increases significantly and upwind windows need to be closed down to 50% (or less), or completely dosed and smle windows open, to give ventilation rates between 6 and 12 ac/h.

• At high wind speeds (5m/s) the upwind windows Med to be closed to 20% or less. Closing down Bind windows is of secondary importance (dosing them to 50% only reduces the ventilation rat« from 11.9 to 10 8 ac/h.).

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