The bituminous road surface of the 80-year-old Howrah bridge will be scraped and a new layer will be laid, Kolkata Port Trust, which maintains the iconic structure, has decided.
In a letter to Kolkata police a few days back, a senior executive engineer of the civil engineering department of the port trust has sought 27 working days to complete the project, which will include repairing the concrete deck slabs beneath the bituminous surface where cracks have appeared.
The road surface of the bridge, unveiled in February 1943, has been witnessing intermittent repairs over the years resulting in the accumulation of layers of bitumen, officials said.
Additional layers of bitumen are contributing to the increase in the “dead load” of the structure, which needs to be urgently reduced, they said.
Dead load, according to engineers, is the weight of the non-movable and permanent parts of the bridge like the steel structure.
The letter, according to a senior police officer, says the road surface of the bridge has not been overhauled for several years and Kolkata Port Trust wants to carry out a thorough repair of “the deck surface of Rabindra Setu”. The letter says the port authorities want to complete the work in a phased manner.
Structural and civil engineers said the repair was necessary to increase the life of the cantilevered bridge, whose formal name is Rabindra Setu.
The addition of layers of bitumen over the decades is believed to be one of the reasons for the collapse of the Majerhat bridge in September 2018. Several bridge engineers had then said the rampant addition of bitumen layers without removing the older ones was threatening the stability of flyovers and bridges by increasing the load on the pillars supporting the structures.
The Howrah bridge is 1,500 feet long between the two towers and the carriageway is 71 feet wide.
The footpaths for pedestrians are 18.5-ft-wide each and the total load of the super-structure is transported to the concrete deck slabs — beneath the bituminous surface — with the help of 78 hangers, port trust officials said.
“The work order for repairing the concrete deck surface of the bridge and its two approaches has been cleared. The approximate cost of the entire project will be Rs 3.5 crore,” a senior official of Kolkata Port Trust said.
Senior officers of Kolkata police said the port trust had sought to complete the work by the end of April. It wants traffic to be blocked in phases — a 200m-long and 7m-wide section in each phase — for the repairs.
“Engineers have sought traffic block at night with a rider. In case a crack emerges on the concrete surface of the deck slab, they will require three days to repair that part,” said a senior police officer.
“We are trying to assess whether we need to introduce traffic diversions similar to the ones enforced during the Santragachhi bridge repairs.”
