Chennai, Mar 2 : A retired Railway Official on Tuesday suggested some changes in the construction of the new Pamban Bridge–with 72 m vertical lift–that connects Rameswaram island with the mainland in Ramanathapuram district of Tamil Nadu and favoured a safer design with suspension bridge concept.
He said the bridge lifting mechanisn should have emergency power supply source located on the shore, either battery storage system or standby diesel generator, besides the completed track should allow accident relief crane movement to carry our any restoration work due to any emergency on the other side. Talking to reporters, Mr T Kuppan, Retired Principal Exeuctive Director, Indian Railways, said as per Rail Vikas Nigam Limited (RVNL) the speciality of this iconic bridge will be the 72 m long vertical lift span. This will allow the lifting of 17 m height to allow ships to pass below the lifted bridge. Referring to the photos and animation under lifting conditions of the proposed bridge released by RVNL, Mr Kuppan said he had examined the design proposed by Railways and found that the proposed bridge might be unsafe since the securing of ends was not shown. It should be lifted and lowered every time a ship passes through it and only a simply supported beam can be lifted vertically easily where a rigidly supported beam i.e., with fixed end conditions can be lifted in slant condition only as in the existing bridge.
The fixed end conditions take the forces due to bending while train passes and the track will be in its position. He said the present cantilever bridge is a fixed end condition beam and hence the bridge span will not move when the train passes over it. Stating that the end conditions of the present slant lifting bridge span is robust where as the proposed new bridge is sleek, Mr Kuppan said it is being pointed out that design of the split bridge by the British India engineers are safer as the end conditions are rigid. ‘Since it is rigid, it cannot be dismantled every time to allow a ship to pass and it can be lifted to achieve a slant condition. Also the bridge is box structure where the load transfer to the end stanchions is undisputable’, Mr Kuppan said.
Referring to the new bridge proposed by Railways, he said once a train passes over the bridge the live load, i.e., train load of one loco+2 fully occupied coaches is transferred to the end stanchion through the bridge box structure and hence the bridge span will not bend and track will be in its horizontal position. In the case of the proposed new bridge, once the train touches the bridge span, it will bend and fall into the sea due the absence of load transfer mechanism to the end stanchion. The proposed 72 m long bridge is of simply supported beam with single span design not supported at the middle (however this is the design requirement) hence the deflection of the beam due to self weight and under dynamic loading conditions when a train passes over it was not taken care.
Mr Kuppan said ‘this design shortcoming can be overcome without introducing middle support, by treating the span as a suspension bridge arrangement duly supporting through cables like Howrah suspension bridge so that the bridge is always supported and hence it will not sag either under static or dynamic condition’. Under dynamic conditions there will be vibration of the suspension bridge and hence it may require speed restriction. Hence, a safer design – suspension bridge concept is proposed.
As per this design concept, the bridge is always safely supported both for static and dynamic conditions, under lifting and lowering conditions. Also the bridge will be supported and a suitable way can be found to avoid entanglement of the suspension cables, while lifting and lowering the bridge.
The Indian designers of vertical lift bridge might been motivated by the existing vertical lift bridges in few countries, but the important criteria is the span length and BG rail road applications, he said. Mr Kuppan, while expressing concern over the frequent explosions in fireworks manufacturing units in the cracker-manufacturing hub of Sivakasi, also came out with a design that would prevent spread of fire to adjacent units and buildings in the event of a mishap.