The load test of the Majerhat bridge started on Monday and will continue till Friday, marking the final stage for opening a vital link in south Calcutta a little over two years since a portion of it had collapsed.

Once the weight-bearing capacity of the structure is found to match the specification in the original design, engineers will run the final check and complete some fine-tuning before declaring the bridge “ready for use”.

“The load test is the last hurdle we will have to clear,” said a senior PWD official.

As part of the test, empty and fully loaded vehicles are mounted on a bridge or flyover and the stability of the structure is monitored. Engineers calculate the load-bearing capacity of the structure and record how different elements — such as the concrete deck slab, bearings and cables (which will hold the part of the bridge that is over railway tracks) — are functioning.

The stress-bearing capacity is monitored with the help of advanced machines and the readings are noted down.

“We will begin by mounting trucks equal to 50 per cent of the load-bearing capacity of the bridge and then gradually scale it up to 75 per cent and finally 100 per cent,” said a senior PWD official. “Several instruments, including dial gauges, will be placed at the end of the piers of the bridge and all deflections induced by stress will be noted down.”

The readings will be taken to the agency that has designed the bridge for an analysis.

Structural engineers will find out whether the stress-bearing capacity of various components are in consonance with the design and whether any deviation has been noticed.

Since 260m of the deck slab of the bridge stands over railway tracks, bridge experts in the railways, too, will take a look at the data, PWD officials said.

The load test of the bridge follows a clearance from the railways. A team led by the chief bridge engineer of the railways and PWD representatives jointly inspected the bridge on November 9.

As many as 84 cables, brought from Switzerland, hold the deck slab of the flyover, which has come up at the site where a span of the bridge had collapsed in September 2018.

“Only 40 per cent of the load-bearing capacity of each of the cables will be utilised,” an official said. “So there is no threat even if there is a sudden rise in the static load on the bridge because of vehicles.”