Project Overview
The new Lambor Bridge connects two communities across the Perak River in one of the key districts in the state of Perak, Malaysia. One of the original goals for this project was to elevate the bridge over the 100-year flood level without creating an unacceptable grade of 9.25% in the approach road.
“Under normal circumstances, the Malaysia Department of Irrigation and Drainage requires all permanent structures crossing rivers to have a minimum 1 meter of freeboard between the 100-year highest flood level and the soffit level,” explains Dr. Fairul Abas , senior bridge engineer, Malaysia Public Works Department.
In this case, the 100-year highest flood level was more than 18 meters. Therefore, the bridge and road would have to be built at an elevation of more than 21.25 meters to meet the grade requirements. However, the road was at an elevation of just 12 meters.
The designer considered extending the bridge back to a local interchange, but this plan was too costly and would have required additional land acquisition, which could have taken up to two years to secure. Another concern was the aggressive heat and humidity, which limited the types of construction materials that could be used. To address the grade and climate challenges, the design team determined that an ultra-high-performance concrete (UHPC) was the best option.
The use of UHPC meant the bridge did not have to be elevated; instead, it could be submerged in the event of extreme flooding because the impervious nature of UHPC would prevent intrusion of moisture and salt. Also, the near total elimination of reinforcing bar would significantly reduce the risk of corrosion and related maintenance costs.
“UHPC offered unparalleled benefits,” says Yen Lei Voo, executive director and CEO of Dura Technology. It meant the final road finished level could set to 16.3 meters so that the gradient of the approach road from the junction is less than 5%. “Lambor Bridge is the first submersible bridge using UHPC where the bridge will be fully covered with water in the event of extreme flood,” Abas says.
Fully Submersible
The bridge surface is designed in a “boat” shape to optimize the hydraulics of water passing through it. The surface is completely smooth, which will accelerate water flow and reduce drag forces. “The boat-shaped bridge girder not only meets the technical criteria of the bridge functionality but also improves the aesthetics compared to normal T-beam or U-beam designs,” Abas says. The extremely low porosity of UHPC increases the structure’s impact resistance and durability in the instance of flooding.
The erection of the bridge presented some unique challenges. Because Malaysia does not have access to expensive launching girders that allow span-by-span construction of segmental bridges, the contractor chose a more practical approach. The first three spans were erected on a temporary steel bridge erected between permanent pier and abutment supports. The remaining five spans were erected on the ground using a scaffold system. In both cases, no span moving was required, and each span took about 13 working days to erect.
“The selected system is believed to be the first of its kind in the world,” Lei Voo says. “Precast concrete is taken to a higher level while still being cost competitive and providing a long, maintenance-free life that is expected to exceed 300 years.” |