Petronas Twin Towers

The Malaysian tallest twin building - Petronas Twin Towers is the anchor project of Kuala lumpur City Center or KLCC. Standing at 451.9M high, it has two towers of 88-storey office building. The Towers were recorded as the world's tallest towers from 1998 to 2004. The tower’s foundationis is about 120-meter depth and were built by Bachy Soletanche with massive amounts of concrete. This is because the depth of the bedrock, the buildings were built on the world's deepest foundations.

The towers are connected at the Level 41 and Level 42 by a sky bridge, 170 metres above street level. The towers are also joined at their base to form a six-level retail and entertainment complex with a central atrium. From the atrium, two ‘streets’, lined with over 300 shops, cafés and restaurants, extend along opposite axes. In addition, the complex includes an 880-seat concert hall, an art gallery, a specialized library and an interactive science discovery centre, as well as a four-storey underground car park for 5,400 cars.

KLCC comprises of:

1. 88 storey Petronas Twin Towers
2. Suria KLCC - the six-level, 1.5 million sq. feet shopping centre
3. 49 storey Menara Maxis
4. 30 storey Menara Esso
5. 32 storey Mandarin Oriental Kuala Lumpur Hotel
6. 20 hectare (50 acre) Public Park
7. Masjid As-syakirin, a mosque which can accommodate 6,000 people
8. 2 District Cooling Centres, which use natural gas to chill water for air-conditioning
   

Basic Information of The Towers.

1. Construction - April 1993–(opened on Aug,31) August 1999
2. Project cost - RM1.8 billion
3. Design/Architecture - Cesar Pelli & Associates (US) in Association with KLCC architects
4. Man at work - 7,000 on the site at the peak of construction and until 1997 there were 1,000 on each tower.
5. Site area - KLCC: 40.5 hectares - Petronas & Retail: 5.8 hectares
6. Built area - 218,000 m2 each tower - 994,000 m2 total Petronas complex
7. Foundation - 4.5m thick raft foundation containing 13,200 m3 of grade 60 concrete, weighing approximately 32,550 tonnes under each Tower, supported by 104 barrette piles from 60m to 115m in length.
8. Tower 1 constructed by The Mayjaus Joint-Venture led by Japan's Hazama Corporation, consisted of JA Jones Construction Co, MMC Engineering Services Sdn Bhd, Ho Hup Construction Co Bhd and Mitsubishi Corporation
9. Tower 2 constructed by SKJ Joint Venture led by Samsung Engineering & Construction Co and comprised Kuk Dong Engineering & Construction Co Ltd and Syarikat Jasatera Sdn Bhd.
10. Concrete(various strength up to grade 80) - 160,000 m3 in the superstructure (5.7mil ft3)
11. Steel - 36,910 tonnes of beam, trusses and reinforcement
12. Number of Storeys - 88
13. Overall Height - 451.9m from street level. Original design was 421m.
14. Height of Superstructure (without pinnacle) - 378m
15. Height of Pinnacle - 73.5 meters
16. Tip of longest pile to tip of pinnacle mast - 592.4m
17. Location of Skybridge - Levels 41 and 42
18. Length of Skybridge - 58.4m (192ft) double-decked
19. Height of Skybridge - 170m from street level (558ft)
20. Weight of Skybridge - 750 tonnes
21. Skybridge Support - Two-hinge arch with rotational pins (spherical bearings) at Level 29, rising 63 degrees
22. Design Consultant - Ranhill Bersekutu Sdn Bhd and Thornton-Tomasetti Engineers
23. Fabricated and assembled by Samsung Heavy Industries of South Korea.
24. Lifting of the skybridge by VSL Heavy Lifting.
25. Vertical Transportation - Total= 76 lifts. 29 Double-deck high speed passenger lifts in each tower. Each double-deck can carry 26 persons.
26. Number of escalators - 10 in each tower
27. Stainless Steel Cladding - 65,000 m2
28. Vision Glass - 77,000 m2
29. No of windows - 32,000 windows
    

SHOTCRETE

METHOD STATEMENT FOR SHOTCRETE


GENERAL

Shotcrete or gunite is a cement motar applied by spraying which contains no coarse aggregate. It can be sprayed over mesh, rock bolts and ribs to form part of integrated support system. The support systems maintain close contact with the rock or ground surfaces to reduce ground movements to a minimum.

MATERIALS

1. The cement to be used shall be Type 1 Portland cement.
2. Fine aggregate shall comply with MS 29 : 1971. The fine aggregate shall be washed.
3. Wire mesh – BRC A4
4. Water/cement ratio ranges from 0.35 to 0.50.

MACHINERIES AND EQUIPMENTS

1. GENERATOR
2. AIR COMPRESSOR
3. CONCRETE MIXER
4. GUNITING MACHINE
5. WATER PUMP
6. STAGING

APPLICATION

1. Shotcrete or gunite is defined as concrete or mortar pneumatically applied at high velocity on to a surface.
2. The cement for shotcrete shall conform to the requirement of BS 12. Type 1 Portland Cement will be used.
3. Fine aggregate (sand) shall clean and free from silt.
4. Fabric reinforcement (wire mesh) shall be hard-drawn steel wire with 7mm diameter wire (BRC A4) complying with the requirements of BS 4483:1983.
5. Mix proportion for cement and sand shall be 1:4. Water/cement ratio ranges from 0.35 to 0.55. The concrete shall have minimum compressive strengths of 10Mpa at 7days and 20 Mpa at 28 days.
6. Suitable air compressors shall be used to provide sufficient air volume to pump the water and the mortar to the discharge nozzle for shotcreting.
7. Loose materials on slope surface shall be cleared before carry out shotcreting process. All rebound and loose material shall be removed by air jets or other suitable means from the surface of each layer as work proceeds.
8. Surplus water shall be removed by air jet. If any water flowing from or across the existing surface it shall be diverted by pipes, hoses or other approved materials.
9. The fabric reinforcement (wire mesh) shall be securely fastened with surface dowel bars at 3m centers and support with spacers to provide sufficient clearance between fabric reinforcement and the slope surface.
10. 50mm diameter uPVC weep holes are then installed at 1.2m centers in each direction.

SHOTCRETING or GUNITING PROCESS - DRY MIX

1. Cement and sand are thoroughly mixed by concrete mixer.
2. Cement-sand mixture is fed into a guniting machine.
3. The mixture is metered into the delivery hose by a feed wheel or distributor.
4. Thus material is carried by compressed air through the delivery hose to a special nozzle. The correct pressure in a dry – mix shortcreting process is normally around 480 – 550 Kpa. Water is introduced to the nozzle with pressure and intimately mixed with the other ingredients. Water is added at the nozzle at a pressure of about 410 Kpa.
5. The mortar is jetted from the nozzle at high velocity onto the slope surface.
6. The spray should be perpendicular to the slope surface to minimize the rebound.
7. No mix shall be used more than 2 hours after any water has been added. Rebound material shall not be reused.
8. To avoid sagging and bleeding, shotcrete shall be built-up successive layers, each layer not exceeding 50mm thickness. The mortar shall cover the fabric reinforcement to a depth of at least 30mm.

SOIL NAILING

Soil nailing is a method to stabilize and strength the existing ground or slope. The basic method is reinforcing by installing threaded steel bars (the nails) into the soil or slope as construction proceeds from top down. The bars are inserted closely spaced pattern to increase its overall shear strength.The steel bars are then grouted to create stable mass of soil. Steel bars commonly be used, with diameters ranging from 15 to 46 mm, stronger than driven nails (about 60 ksi). Grouted nails are inserted into boreholes of 10-15 cm and then cement-grouted.
The cement grouting process is by injecting the Grade 30 cement with water/cement ratio is about 0.45 to 0.5. The cement grout shall be carried out by tremie method. 0.75” to 1” diameter HDPE grout hose is inserted into the borehole and grout tremie out under a normal pressure of about 0.7 MPa or just enough to pump the grout into the borehole. The grouting process shall be continued until neat cement grout flows out from the bore holes. If temporary casings are used, the casings shall be removed by immediately after grouting work is completed. During and after removal of casing, the grout column is to be topped up when necessary.
Soil nail bars shall be locked. Stressing or locking of the soil nails shall only commence after a minimum of 5 days curing period or when the cube strength for the cement grout achieved 75% of design strength. Stressing or locking of the nail bar shall be by either a hydraulic jack or simply by a torque wrench to the required load 5kN. Soil nail head shall be constructed after stressing work finished.

Soil nail construction has many advantages:

• Soil nail walls can be built to follow curved or zigzagged outlines.
• The equipment used is highly portable and can fit easily into small spaces.
• The process is flexible and makes modifications easy to carry out (e.g., nails can be moved as needed during construction).
• Construction causes less noise and traffic obstruction on highways.
• The process creates less impact on adjacent or nearby properties than do other construction methods.
• It generally requires less space and manpower