Pune Metro Update: Launching of Structural Steel Girders for Harris Bridge

Launching of Structural Steel Girders for Harris Bridge by Incremental Launching method for Elevated Viaduct of Reach-1 in Corridor-1 (PCMC-Swargate) for Pune Metro Rail Project. The alignment of the Pune Metro Rail Project on Reach-1 of Corridor-1, on the elevated viaduct, is crossing river Pawana near Dapodi. 

• This river crossing is through Harris Bridge consisting of 11 no’s of spans (HB1 to HB12), out of which 7 no’s of spans (HB1 to HB4 & HB9 to HB12) is located on the approach of the river on either side and, 4 no’s of spans (HB4 to HB8) are located in the river portion.
• All 11 spans are designed with structural steel composite girders. 
• The span-wise span lengths of the Harris Bridge from HB1 to HB12 is 25.1m, 43.5m, 45.75m, 28.42m, 43.59m, 42.98 m, 43.08m, 43.5m, 40.0m, 40.0m, and 34.09m respectively. 
• Each span consists of two sets of two steel girders of 2.422m depth kept side by side and both the girders of each set are connected by cross bracing. 
• The weight of one girder varies from 21.5 MT to 47.5 MT and the weight of all 4 girders of one span varies from 85 MT to 220 MT. 
• Erection of 7 structural steel girders on either side of the river is done by Tandem Lifting Method in which the steel girders are first assembled at ground level and then lifted and placed in position with the help of two road cranes of required capacity which are handling each set of steel girder from either end. 
• However, a girder erection of central 4 spans, piers of which are located on the river bed, was not possible by Tandem Lifting Method due to constraints of placing heavy capacity road cranes on the deck of existing road bridges, as the existing road bridges are old structures. 
• Hence, Incremental Launching Method was adopted for 4 central spans (HB4 to HB8) within the river bed.

Incremental Launching Method (HB 4 to 8):

• The temporary supports are erected within approach spans for supporting the steel girders temporarily before they are launched by incremental method into their final locations. 
• Hillman & guide rollers are fixed on each temporary supports for the movement of the steel girders. 
• The capacity of the Hillman roller is 100 MT and 02 nos of Hillman rollers are provided on one temporary support. 
• Total 22nos of Hillman rollers were provided. 
• Side rollers are also provided to guide the pulling direction of girders to ensure that girders move in the desired direction. 
• One set of two plate girders of the first two spans is first assembled on erected temporary supports.
• The splicing of these girders is done to make a longitudinal continuous member facilitate their movement during the pulling process. 
• After connecting wire rope arrangement, the whole assembly of plate girders is pulled with a winch machine for about 43m. 
• The capacity of pulling the winch is 20MT. 
• While the girders are being pulled from the PCMC end, the restraining winch of equal capacity 20MT is also provided on the PMC end to avoid any accidental slippage of girders during the pulling or pulling getting out of control. 
• After completion of the first set launching, the next set of two plate girders of the last two spans is assembled on erected temporary supports. 
• These two girders shall be attached to the already pushed girder back with splicing. 
• Now the whole assembly of four girders shall be pulled with the winch machine. 
• Once a set of two girders are pulled and placed in their final designated position under the track and the same procedure is adopted for the other side pair of two girders also.
• After the completion of pulling off all four girders, the girder shall be lowered on bearings for final alignment and further construction activities.

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Source: Pune Metro