The Petronas Twin Towers, the world’s tallest skyscrapers today express very beautifully the Malay Islamic culture and heritage of Malaysia. They acknowledge Malaysia’s past and future and at the same time people the energetic city of Kuala Lumpur to modernization, adding a bright page to architectural history. With the construction of the Twin Towers, Kuala Lumpur’s prominence as a commercial and cultural capital is well established. Kuala Lumpur is one of the world’s largest construction sites and is in the wake of a construction revolution. The soaring twin cylindrical towers appear to embrace their smaller adjoining wings connected by a sky-bridge. Fundamental principles of Islam, the prominent religion in Malaysia, form the basis of the geometric design used in the floor-plate of the tower. Two rotated and superimposed squares with small circular infills symbolize unity, harmony, stability, and rationality. The exterior designs of the Towers as well as entrance design are predominantly Malaysian in culture. Although the overall character of the building is high-tech and international, it remains distinctively Malaysian. Located on the northern boundary of the Multimedia Super Corridor (MCS), having state-of-the-art communication facilities, the Petronas Twin Towers have catapulted Malaysia to the frontline of the information era.
Criteria for Ranking Towers Based on Heights
The Council on Tall Building and Urban Habitat, representing world leaders in the field of the built environment, research industry, and education are vested with the final authority on tall buildings. Official criteria are used by the Council in determining to rank.
A building is defined as a structure designed for residential, business, or manufacturing purposes. Floors are an essential characteristic of a building.
The height of a building is measured from the sidewalk level of the main entrance to the structural top of the building spires are included but television and radio antennas, flag poles are excluded. The final determinant in ranking a building’s height is the footage as it has a smaller, more precise incremental value.
The ranking is determined by height to the structural top of the building in case of a tie, the building with the larger number of stories is ranked higher. In case the tie still remains, the building, which was complete first, is ranked higher. If a tie would still remain, the building would be ranked alphabetically.
Prominent Features of Petronas Twin Tower
The main features of the Petronas Twin Towers are as under:
- Double – Deck sky-bridge at Levels 41 and 42.
- High-speed Double–Deck Lifts.
- Building Control System.
- Building Security System.
- Communication System.
Architecture and Design of Petronas Tower
Petronas Towers standing 452 meters high in Kuala Lumpur, Malaysia were designed by the Argentinean-American architect Cesar Pelli. Petronas, Malaysia’s national oil company wanted to build the world’s tallest building. Construction of the twin skyscrapers was completed in 1998 surpassing Chicago’s Sears Tower as the record-holding tallest structure. Built of steel-reinforced concrete columns, clad in stainless steel, and glass, the design resembles motifs that are found in Islamic art. The 88-story skyscrapers are linked at levels 41 and 42 by a double-decker pedestrian sky-bridge. Each tower is surmounted by a 74-meter aluminum-faced stainless steel spire.
The towers are entirely devoted to office space. Below the towers is a shopping complex. The Dewan Philharmonic, a concert hall, a showpiece in architectural and acoustic terms is located in the podium block. There is a meticulously planned park with fountains, pools, jogging tracks, and many trees outside the shopping mall.
The designers wanted the architecture to be typically Malaysian. But there was little Malaysian architecture to refer to. Hence the architects, Cesar Pelli & Associates created the geometry of the towers based on Islamic geometric traditions- on two interlocking squares. The fundamental square stands for the earth and its four cardinal points. Complexity represents the incomprehensibility of God. The interlocking square creates an eight-pointed star on which eight semi-circles are superimposed in the inner angle of the star, which creates a 16-branched form. Each of the 16 inner angles contains smaller semi-circular forms expressing the main structural columns of the building.
Each tower has about 185806 m2 of office space. The project’s usable floor space was enhanced by 43-story cylindrical buildings attached to each tower. A two-level, 53-meter steel girder “Sky-bridge” connects the towers at the 41st and 42nd levels, also serving as a fire exit. Tow V-shaped, tubular steel legs rise from the 29th floor of each tower to support the bridge at mid-point. The ends of the bridge girders rest on sliding bearings allowing the towers to move 0.254 meters.
Foundation System and Soil Strata
A serious study of boreholes revealed that ground conditions comprised of three distinct foundation strata:
- Alluvium
- Kenny Hill formation of clay and silt
- Limestone formation varying in depth from 20 m-200 m eroded in places into cavities.
After construction of the diaphragm wall, the site was excavated to a depth of 20 meters and the wall was anchored into the ground. The final foundation consisted of a 4.5-meter thick raft located 19 meters below ground supported on 1.2 m x 2.8 m rectangular friction piles. Each tower rests on 104 piles varying in depth from 60 m to 115 m below the raft level. The pressure grouting technique was used to treat all cavities in the limestone down to 150 m as also weak zones at the interface of the Kenny Hill and limestone formation.
Each tower stands on a 4.42 m thick concrete mat supported on 85 concrete friction piles, some as deep as 121.8 m. friction piles were then constructed and the 4.5 m thick foundation raft was poured to cap the same. Each mat contains 13375 m3 of 60 Mpa concrete using 9% silica fume and was cast in a single, 54 hours pour. In order to maintain the temperature of the raft below 90oC, chilled water, and cooled aggregate was used. 50 mm thick polystyrene was used to insulate the top of the raft and the sides were covered with precast formwork panels.
Chilled water was used for mixing, aggregates were cooled by spraying and water content in the sand was kept at a minimum. The top mat was insulated using 50 mm thick polystyrene and the sides were covered with precast formwork panels to prevent a large temperature differential. The temperature gradient was constantly monitored and measured by means of thermocouples placed in the mat. The whole process from excavation to completion of the foundation’s tool 12 months.
The 19 m deep podium is made up of six levels and is retained by a 30 m deep, 0.8 m thick diaphragm wall, about 970 m long. Columns outside the footprint of the towers supported the podium and the car park, which are founded on spread footings with a drained slab system.
Construction of the Basement
Underground structural work was required to provide parking slots for office staff, shoppers, and others visiting the complex. Basement construction was started when the foundation and the diaphragm wall were in place and the basement excavated to 20 m. the initial work was to construct the foundation mat and reduce the uplift pressure on the foundations caused by groundwater. Sand piles 1 m in diameter, 8 m deep and 8 m center-to-center were bored and a 450 mm layer of high-grade filter sand was poured in. Slabs ranging from 1.2 m to 2.9 m thick were poured to form the drained mat. Drainage holes in the foundation slabs connected to the sand piles below permitted groundwater to seep up into the slump pits from where it was pumped out to ground level. The conventional column and slab method were used for the construction of the basement. Nearly 17400 m3 of concrete, 19800 MT of steel, and 341424 m2 of formwork were required for the construction of the basement.
Superstructure
The structural system was adopted after extensive computer modeling and wind tunnel testing. The structural frame is capable of resisting both vertical and lateral loads subjected to wind forces at different speeds. A structural steel floor system was used to achieve this.
Each tower has an outer ring of 16 columns that are about 2.44 m in diameter, made of 10,000 psi (70 N/mm2) concrete that form a 45.67 m diameter circle. The columns taper as they rise and slope inward to accommodate setbacks. At each level, the ring of the column is connected with a haunched ring beam. Lateral loads are shared by the columns and the 22.8 m x 22.8 m concrete core through floor diaphragms. The floors are composite metal decking and steel infill beams.
The Petronas Towers are a “soft tube” with up to 2.4 m dia reinforced concrete columns 8 m to 10 m apart connected by a haunched ring beam at each level. The “soft tube” is connected to a reinforced concrete core through floor diaphragms. In a system like the soft tube, 50% of the overturning is taken by the core and the rest by the exterior tube. Outriggers have been provided in the Petronas Towers as they provide very strong floors.
The two Petronas Towers, through identical, were built by different contractors. The shell and core of Tower Two as also the sky-bridge was built by one joint venture and the shell and core of Tower one by another joint venture. Details are given in the point titled “Credits”. The Tower two contractor claimed a concrete pumping record, raising concrete 379.42 m in one lift. Contractors of both the towers used self-climbing forms columns, core, and beams.
Concrete grade of 80 Mpa was used 22nd level and 60 Mpa was used above the 22nd level. A total quantity of 1,60,000 Cum was poured into the superstructure of these towers and 36,910 MT of steel was used. Typical details of 80 Mpa concrete supplied by ready mixed concrete plants are below.
Details of 80 Mpa Concrete Mix (upto Level 22)
| Material | Quantity |
| Cement Mascrete Micro silica W/C 20 mm Aggregates Sand Slump Strength at 56 days | 260 Kg 260 Kg 35 Kg 0.25 to 0.27 1000 Kg 700 Kg 18-22 mm 100 Mpa |
The structure is high-strength reinforced concrete, a material that is twice as effective as steel in sway reduction. Supported by 22.8 m x 22.8 m concrete cores and an outer ring of widely spaced super columns. The towers showcase a sophisticated structural system that accommodates its slender profile providing 1300 sqm to 2044 sqm of column-free space per floor. Each of the twin towers is 88 stories plus an additional architectural point at 378 m plus a tall spire to 452 m. The towers have 32,000 windows. A prominent feature includes a curtain wall of glass and stainless steel sun shades to diffuse the intense equatorial light. A double-decker elevator system with a sky lobby transfer point on the 41st floor accommodates thousands of people who use the complex daily. A mixed-use base featuring a concert hall and shopping center is enveloped by about seventy acres of public parks and plazas.
Sky-bridge
The Double-Deck sky-bridge is a prominent feature of the Petronas Twin Towers. It is an essential functional component linking the two towers to facilitate movement between them. The 58.4 m double-decked sky-bridge located at levels 41 and 42 joints the sky lobbies situated in both the towers.
Engineering Design of the Sky-bridge
The structural system selected utilizes a “two-hinge arch” springing from supports at level 29, rising at 63 degrees to support a pair of parallel two-span continuous bridge girders at level 41. The structure of the sky-bridge is traditional framing constructed of structural steel with beams moment-connected to columns that bear on the level 41 continuous girders. It is 58.4 m long, weighing 750 tonnes. The two-hinge arch supporting the bridge has rational pins at the end of each “leg” or “spring point” and at the “top” or “crown” of the arch. The main bridge girders have a rational pin directly over the arch crown to permit the crown to rise and fall as the towers move closer or further apart. The arch is a centering device, equalizing joint movement at both towers. As the towers move apart or together, the legs change slope, the spherical bearings rotate at spring points and the legs flex at their top end. The bridge mid-point rises or sinks, flexing the two main girders.
The girders are pinned on the arch crown, which stays centered between the towers, while both girders & blocks slide on pads. The mid-span centering pin and two girder slip pads accommodate this movement.
Continuous expansion joints have been provided through the level 42 and 43 structure, façade, and roof to each side of the bridge mid-point. Expansion joints or Movement joints provided at mid-point reduces the effect of girder flexure on bridge glazing, as window panel movement is then limited to each half-span rather than cumulating over the whole girder length.
When the towers move side-to-side in opposite directions or when they “twist”, the arch spring points twist on the spherical bearings and bridge and bearing slide in opposing directions guided by “sliding keeper” blocks on the bridge centerline.
In the event of losing its arch support, the bridge structure will not collapse but deflect and stay in position.
Assembly of the Sky-bridge
Fabrication
The sky-bridge was fabricated and shop assembled by Samsung Heavy Industries of South Korea. Fabrication works compiled with some of the most stringent codes and standards.
The fully assembled bridge was dismantled and shipped to Kuala Lumpur in 493 pieces weighing 452.64 tonnes. To facilitate putting it into place, the sky-bridge was pre-assembled into five main components comprising the two end blocks, two legs, and the center section.
Centre Section
The 307 parts of the frame for the center section were fully assembled and bolted. The center section of the sky-bridge frame, measuring 41 m in length, over 5 m in width, and 9 m in height was assembled at the concourse level.
The center section’s internal floors and roof at levels 41, 42, and 43 were constructed in metal decking. After the roof level concrete slab was placed the whole assembly was painted & the external building maintenance equipment for the legs installed.
Sky-bridge Legs
The two inclined legs are approximately 42.6 meters long and weigh about 60 tonnes each. The five sections of each set of legs were assembled and checks on the whole dimension, camber, and alignment were made before bolting. Tuned mass dampers have been engineered for the legs. Dampers have been designed after a thorough wind tunnel test to accommodate the comfort level by dampening any effects of wind conditions and possible long-term fatigue due to resonance of the legs. These pendulums-operated dampers were field-tested and inserted into the center section of the legs just prior to the final assembly.
End Blocks
The two end blocks of the sky-bridge were assembled at concourse level with main girders, crossbeams, and horizontal bearing. The two end blocks are approximately 8.3 meters long and weigh each. After checking the whole dimension and alignment of the end blocks, they were ready to be lifted.
Lifting of the Sky-bridge
Studies and presentation of the lifting were carried out for more than a year in the United States and South Korea, simulating various wind and weather conditions over the past 50 years.
Lifting of the sky-bridge was undertaken in nine steps described as under:
- The sky bridge’s legs were lifted up one at a time by tower cranes. Once they were in position, control cables were used to lower them over the permanent bearings at level 29.
- The two end block girder frames of the sky bridge were lifted individually. The blocks were installed about 100 mm above their final position at level 41. They reacted about 100 mm into the tower to provide clearance for the sky-bridge section during lifting.
- The four lifting jacks located at level 50 of both towers were connected to the bridge center. The other four lifting jacks located on level 48 of both towers were connected to the bridge ends.
- The center section weighing 325 tonnes was lifted about 11 meters and restrained.
- After the final checking lifting of the center, the section was begun.
- The center section was gradually lifted to its final level at a lifting speed of 12 meters per hour.
- A temporary connection secured together with the center section and the end block girder frame to ensure that there was no stress.
- The legs were moved into their final position and the sky-bridge end blocks were lowered on their permanent bearings at level 41.
- After the lifting system was removed, the floors were concreted and the sky-bridge roofed. Maintenance equipment was set up on stainless steel rails on top of the bridge.
The entire lifting operation of the sky-bridge at the 41st and 42nd levels of the Petronas Twin Tower took nearly 32 hours.
Cladding and Vision Glass
A continuous wooden screen is used for the perimeter of the lobby wall reinforcing the tropical locale and optimizing the use of Malaysian craft tradition. The Petronas Towers is located in the tropics, the sun is less welcome and the views are important. The windows run in continuous horizontal ribbons of vision glass to take advantage of the breathtaking view all around. They are narrow and of modest height. Projecting shades protect them from the sun.
The towers are completely clad in stainless steel. The sculpted horizontal articulations reflect the sunlight and shine like the facets of a crystal giving the Tower a specific sense of their tropical locale. Stainless steel was chosen for its durability and for the image of a new Malaysia.
Elevators
The Petronas Twin Towers are serviced by a total of 76 lifts, out of which 58 are double-deck lifts. The double-decker lifts result in better utilization of the core space and require less hoistway. The efficiency of passenger transportation is thus maximized. The system features two passenger cabs, one above the other in the same car frame, sharing the same hoistway. Each double-decker lift can carry 26 persons per deck.
Shuttle elevators can carry 26 persons per deck or 52 per one trip. Each of the other double-deck lifts is designed to take 23 persons per deck.
Traveling time is between 3.5 m/sec and 7 m/sec depending on the zone being serviced.
Dewan Philharmonic Petronas
The Petronas Concert Hall, designed by Cesar Pelli and Associates is located in the podium block of the Petronas Twin Towers. The 864-seat world-class venue is the home of the Malaysian Philharmonic Orchestra.
Telecommunication and Building Security Systems
The building management system is a structured cabling system consisting of vertical, horizontal, interbuilding cabling, and connectivity to telecommunications carrier companies. A special feature of the Petronas Twin Towers is the raised flooring that facilities cabling and provides flexibility in the installation of workstations, communication, and electric equipment.
The telecommunications infrastructure is designed as a local loop communications system within the boundaries of the site. The Central Telecommunications Office (CTO) is the hub of the system which serves as a local communications exchange and gateway to the outside world.
Network availability and reliability are ensured at all times. The workstations are connected to an optic fiber network that is capable of handling state-of-the-art information technology applications.
The building security system is designed to operate via a local area network (LAN).
Sub-System includes:
- Card Access and Alarm Monitoring System
- Voice Intercoms
- Alarm Monitoring System
- Audio Alarm Surveillance System
- Closed Circuit Television System – CCTU
- Photo Identification System
High-level software captures all data to ensure fully automated co-ordination among the sub-systems.
Petronas Twin Towers – At a Glance
| Number of storey | 88 |
| Height | 452 m above street level |
| Total built-up area | 341,760 m2 |
| Design/Architecture | Cesar Pelli & Associates (U.S) in association with KLCC architects. |
| Location of Sky-bridge | Levels 41 and 42 |
| Length of Sky-bridge | 58.4 m |
| Height of Sky-bridge | 170 m above street level |
| Vertical transportation | 58 double-deck high speed passenger lifts in both tower |
| Number of escalators | 10 in each tower |
| Stainless steel cladding | 65,000 m2 |
| Vision glass | 77,000 m2 |
| Concrete (Various strengths up to grade 80) | 1,60,000 m3 in the superstructures |
| Steel | 36,910 tonnes of beams, trusses and reinforcement |
| Foundation | 4.5 m thick raft containing 13,375 cubic meters of grade 60 reinforced concrete, weighing approximately 32,550 tonnes under each tower, supported by 104 barette piles varying from 60 m to 115 m in length. |
| Formwork and Scaffolding | PERI-HORY Malaysia Formwork Sdn. Bhd. |
| Tenant | KLCC Holdings Sdn. Bhd (Tower II) |
| Tenant | McKinsey & Company (Tower II) |
| Tenant | Petroliam National Bhd. (Tower I) |
Some Interesting Details
One morning in 1997, French urban climber, Alain “Spiderman” Robert scaled the Petronas Towers exterior glass and steel wall all the way to the top, using only bare hands and feet, with no safety devices of any kind and without warning.
Most of the construction work has carried out at night while finishing work was done during the day to save on the cost of artificial lighting.
At the peak of construction there were 7,000 workers on the site.
Problem Faced During Construction of Petronas Twins Towers
Maintaining the vertically of the building, including the loading of the 750 tone sky-bridge 170 m above the ground was the main problem. Permanent survey markings and the latest global positioning system were used to check the vertically every day and every night. In order to minimize misuse, the same person used the same instrument at the same time every 24 hours.
The likelihood of settlement was another problem as the load was 2,70,000 tone per tower. Some built-in features such as a 25 mm deflection gap between slab wall and ring beam, permanent survey markings, and gauges to check for column shortening were done.
A major challenge was the sky bridge. Generating and studying computer models of different bridge designs took 6 months before, finally adopting the 3 pins arched design. Fabrication and assembly work lasted for several months while the lifting operation was done over a period of 4 weeks.
Fabrication of the 73.5 m high structural steel pinnacle at the top of each tower took 19 weeks in the workshops in Japan, Korea, and Malaysia. Lifting and erection of each 176 tone pinnacle was a challenge. Partially assembled sections were lifted in sequence. A hydro-jacking system ensured that the tiny 3 mm tolerance from the vertical was met and the entire operation took 3 days.
Conclusion
The Petronas Twins Towers have raised the curtain on New Asia. Among reinforced concrete buildings, this stunning architectural triumph has added a bright page to architectural history.
However, the attack on the twin towers of the World Trade Center has created national and international debates on subjects concerned with the future of super-tall buildings. Design and construction professionals are learning how to better design blast resistance into at-risk buildings. The need to improve codes or create a model code for super-tall buildings is being increasingly felt. Whether or not to replace the twin towers with an even taller icon has also been considered.
In the midst of controversy, Cesar Pelli, the designer of the Petronas Twin Tower states, “The only way to demonstrate our strength would be to build two towers of similar size. I don’t see why we should capitulate to a group of criminals”.
Professionals the world over are not cowed by attacks and they feel there is no stoppage to development plans and additional consideration will be given to icon buildings. There is still enthusiasm for building tall. Experts are considering how to improve resistance to attack through fine-tuned structural systems improving emergency access, egress, and better life safety systems.
