Fast Track Construction of Viaducts of Bangalore–Hosur Elevated Expressway

Abstract

The project of Bangalore–Hosur elevated expressway comprises 10 km of elevated viaduct, a complex traffic interchange, two flyovers, several vehicular underpasses and pedestrian underpasses (VUPs and PUPs), as well as ground level roads. The owners laid emphasis on the riding quality and made it mandatory for the contractor and designer to keep the spacing of the expansion joints at a minimum of 262 m. The elevated viaduct has been constructed using a precast segmental continuous superstructure over the spans (29 m + 6 × 34 m + 29 m = 262 m). The sharply curved interchange superstructure has been conceptualised as a cast-in situ reinforced cement concrete (RCC) voided slab with spans ranging between 20 and 35 m. The two flyovers comprise a continuous girder-slab superstructure incorporating precast post-tensioned girders. The VUPs and PUPs have been constructed using the box pushing method. All earth-filled approach ramps have been conceptualised as reinforced soil embankments.The eight span continuous superstructure of the elevated viaduct was constructed in eight stages comprising 1¼ of span, ¾ + ¼ span, ¾ + ¼ span, ¾ + ¼ span, ¾ + ¼ span, ¾ + ¼ span, ¾ + ¼ span, and ¾ span. The analysis and design had to carefully simulate a structural model in order to account for stage wise prestressing, hyperstatic effects and creep redistribution, apart from the applicable primary loading. Where the stilted approach ramps joined the main viaduct, the expansion joints of the two structures were so aligned to have the same longitudinal expansion and contraction, such that the expansion joint material along the longitudinal joint between the two structures behaved satisfactorily. Speed of erecting the single-cell box superstructure for each span of the 262 m long module was about 3½ days. As the single box-girder carried two carriageways, the speed was about 1¾ days per carriageway span. The main attributes to the speed of construction were the use of wireless remote controlled launching girder, matching speed of production of precast segments that were produced using short bench method, and the prefabricated reinforcement used to speed up the precasting process. An adequate number of trailers were employed for transportation.