Airport Terminal 1D canopy collapse: Panel blames ‘inferior workmanship’, DIAL says it is ‘satisfactory’

DIAL had then stated that the primary cause of the collapse seemed to be continued heavy rain, pointing out that the city had received the highest 24-hour rainfall on June 28 — the day of the incident — since 1936.

In a report submitted to the Directorate General of Civil Aviation (DGCA) on October 1 last year, the committee had flagged discrepancies in design, workmanship, and maintenance as possible reasons behind the canopy collapse and recommended measures.

The Indian Express has accessed the report under the Right to Information Act.

Talking to The Indian Express, a DIAL spokesperson said it had responded to the committee with additional information, design calculations, and test reports of National Accreditation Board for Testing and Calibration Laboratories (NABL)-accredited agencies, proving that the “design and the workmanship are satisfactory”.

The committee found that the canopy collapse was primarily caused by the failure of a welded joint at a key connection between a horizontal beam and a flared column. In its report, the committee said the design had assumed the beam to be connected at the top of the column, but on site, it was welded “at an intermediate level below the top ends”, which changed the path through which forces were transferred and increased stress at the welded joint.

“Most of the welds were not properly executed,” the report said, pointing to “inferior workmanship in fabrication and execution, particularly welded connections”.

“Incessant rain caused an accumulation of water on the roof, and the capacity of the welded connection was finally breached,” the report said, specifying that the final trigger was the incessant rain, and the weld cracked due to its inferior quality. It added that once the joint failed, the structure experienced a “sequential failure of different structural elements”.

The report also found that the live load was underestimated. While the Bureau of Indian Standards (BIS) mandates 0.75 kPa for such structures, the report noted that only 0.5 kPa had been considered. It also said the design had not adequately accounted for rainwater accumulation.

“The detailing and design of connections, particularly welding connections, have not been carried out adequately. In the absence of any documents, it appeared that this important aspect was left to the fabricators for their own interpretation/execution,” it added.

The panel recommended a thorough inspection and investigation by a specialised agency of the portion of the canopy which did not collapse.

The DIAL told The Indian Express that the said structure was found safe in an inspection carried out by Cortex Construction Solutions, and the test results validated by IIT Banaras Hindu University. The structure was also studied by L&T’s Engineering, Design & Research Centre (EDRC) before reconstruction works were started.

Asked if the seismic force calculations and load transfer mechanisms flagged in the IIT report had been re-evaluated, DIAL said these had been checked and were “as per standard IS code provisions, and no lacuna”. It also said design earthquake forces for the non-collapsed structure had been compared with original assumptions and “found to be in order”.

On the committee raising concerns about the use of “stub plates” – thin welded plates used to support purlins – which it described as “not a suitable structural element for taking the loads”, DIAL said, “Stub plate load carrying capacity was found to be in order,” adding that no stub plates were found to be inadequate.

On the issue of drainage, which the panel said may have contributed to water accumulation over the collapsed section, DIAL said modifications had been carried out.