Tuesday, August 31, 1999

Gateway in the sky By Grace Chin

STANDING at 170m and connecting two levels - 41 and 42 - of both towers, the skybridge symbolises the gateway to the City Centre, and the doorway to the infinite.

Certainly one wrong step would send many to infinity too and that was why the bridging of the towers had to be done slowly and carefully.

According to then project engineer for the civil and structural department of KLCCB (Kuala Lumpur City Centre Berhad), the skybridge had always been in the plans although the initial design was not what it is now.

One leg secured and another to go.

"The bridge was designed to be supported by cables at first. But the engineering consultants soon realised that the cable system was not effective enough accommodate the bridge movements caused by the wind factor."

It was only after studying numerous designs, the wind tunnel factors and structural options using state-of-the-art computer simulations that the engineers arrived at the final design of the bridge.

"The final design was simplified to accommodate the movements caused by the wind. We made a model of the bridge and placed it in a wind tunnel environment that was supplemented by a 3-D computer simulation before we went ahead with the construction."

Instead of the cables, a two-hinge arch rising from supports at level 29 at 63« propped up a pair of parallel two-span bridge girders located at level 41.

The two-hinge arch has rotational bearings at the end of each leg that allows the legs to move 300« in strong winds.

The skybridge - 58.4m in length and weighing 750 tonnes - was fabricated in South Korea by Samsung Heavy Industries and pre-assembled to ensure they fitted before being transported to Malaysia.

The last phase of the completion of the bridge, with both block ends welded to the towers and legs attached to the box girder beneath the midsection.

Comprising 493 pieces, the skybridge arrived at the KLCC site in the first week of May 1995.

There were many discussions as to how to put the bridge in place, including constructing the bridge piece by piece in mid-air!

"We finally decided on the heavylifting technique which uses hydraulic jets and cables."

The day came when the bridge would make history by being lifted to its place - July 6, 1995.

The bridge was assembled at the concourse level into five components - the two legs, two end blocks and the centre section.

It was fair and sunny weather when Prime Minister Datuk Seri Dr Mahathir Mohamad came to launch the event by pushing the lever that would start the lifting process.All went according to plan and schedule - until the weather changed.

"The storm struck in the evening and we had to stop the lifting right where it was. We waited quite a few anxious hours before we could resume," recalls Mohamad.

When the hoisting started again, those were some of the longest hours for him and his colleagues.

The planning manager of the KLCC project, remembers there were heart stopping moments when the wind was "really strong and we had to stop."

"We were worried that the cables would sway and snap in the wind."

"Nobody slept that entire time as we were excited and anxious to see to its completion. If we missed it, that was it. It was a once-in-a-lifetime experience which we would never have again."

Because of the wind factor, it took Samsung over 30 hours to lift the skybridge and put it in place.

The legs were lifted one at a time and at a certain height, each leg was manoeuvered into a vertical position. Then control cables lowered the legs to their bearings where they were secured and held "upright" by a holding frame.

Then the two end blocks of the bridge were lifted individually, supported temporarily by a tie approximately 100mm above their final position to provide enough space for the midsection that came last.

The midsection, with the girder box from which leg stubs that would be connected to the two legs, came last.

Bearings allow bridge legs to flex as the towers move in the wind.

Once the midsection was in place, the end blocks were welded at both ends and the legs lowered until they met the leg stubs attached to the box girder and were secured.

"When it was completed, I felt this sense of achievement. I think we all did. Any single activity could have collapsed which would have affected the entire operation and we could have failed."

"We overcame all these technical difficulties and it's thanks to the teamwork of everyone involved that we got the skybridge to where it is now."