This project was for the construction of a flyover above the existing Jalan Tun Razak bridge and roundabout. It connects the busy commercial area at Jalan Sultan Ismail with the housing area of Jalan Kampong Pandan and the scheme objectives were to improve traffic circulation and access to the roundabout.

 

At the same time, there were two other projects in progress – the SMART tunnel and KL-Putrajaya Highway Ramps. The original method of construction was detailed as precast segmental construction span-by-span, using an expensive overhead launching gantry. If the handing over of a pier were to be delayed due to other contractors, the launching gantry could not advance forward.

By adopting an alternative design, based on balanced cantilever construction using form travelers, the sequence of construction could be changed according to availability of piers – giving the advantage of both flexibility and economics. BBR Malaysia, through the use of form travelers and prestressing

technology, combined with CEPAS’ finely-tuned and well-proven design expertise, optimized the design and construction method for the superstructure. The owner’s requirements were to maintain the span lengths, shape and outer dimensions of the bridge superstructure.

The flyover is a multi-span bridge structure consisting of 12 spans with an overall length of 568 m.

• Part A: 40 m + 56 m + 56 m + 40 m Total = 192 m
• Part B: 40 m + 56 m + 56 m + 48 m + 40 m Total = 240 m
• Part C: 40 m + 56 m + 40 m Total = 136 m

Parts A and C were built using conventional staging over existing median. After stressing the longitudinal BBR CONA 1906 tendons, the strands were coupled using Kcouplers to construct the next span. Part B was carried out using the balanced cantilever method because of the busy traffic at the roundabout and existing Tun Razak flyover. The superstructure consists of two single cell box girders of varying depth from 3.2 m to 2.4 m. The two box girders are structurally independent of each other by a gap of 200 mm. Each box has a 9.45 m deck width, designed to carry two carriageways.

Due to site constraints and in order to minimize the interference with the existing traffic flow, most of the piers were formed by a single column with a wide crosshead. The prestressed crosshead is capable of carrying two single cell box girders which are monolithically connected to the crosshead. This was made possible by combining the crosshead with the diaphragm. Transverse tendons, consisting of ten BBR CONA 1906 tendons, were provided to transfer the loads from each box girder to the single central pier. This prestressed diaphragm crosshead is also monolithic to the single pier. The top of pier was enlarged into a flare head which is aesthetically pleasing. Such a monolithic connection without bearings also fulfilled the stability requirements in the construction stages of the free cantilevering construction.

The balanced cantilever method is commonly used for spans from 100 to 250 m – so this case of 56 m span maximum is somewhat unusual. This is possible due to the peculiar circumstances of this project and the availability of travelers lent to us by our Singapore cousins – a very big THANK YOU to them. This is a fine example of the benefits of the international BBR Network – being able to share such resources. In a typical tendon lay-out for free cantilevering construction, the cantilever tendons are usually stressed at one end only, depending on the construction cycle. The anchorages of the cantilever tendons are placed within the deck slab as close as possible to the web. The span bottom tendons are pulled through the ducts after the closure gap and anchored at blisters within the box. The following types of prestressing tendons were used for the Kampong Pandan flyover:

• Cantilever tendons: BBR CONA 706
• Span tendons: BBR CONA 1206 and 1906

The construction was so flexible that a mixed construction method was chosen for piers P5 and P8 to speed up the work. The segment on one side was cast on temporary staging, while the segment on other side was completed using form travelers.

The key benefit of the prestressing technology has been to enable balanced cantilever construction which was a necessity here to ensure that there were no interruptions to the flow of busy traffic at the roundabout and on the flyover.

By combining tendons with form travelers, a flexible method of construction was used to construct the Kampong Pandan flyover in an efficient and timely manner, despite being in the midst of other ongoing projects. The prestressed diaphragm crosshead over a single pier to carry two box girders provided an elegant and effective way to carry the loads to the substructure.