Poor lateral support led to metro pier crash in Bengaluru: Report

A team of professors from the civil engineering department of IIT Hyderabad, commissioned by the Bengaluru City Police to identify the causes for an under-construction metro pier crashing and killing a woman and her toddler son in HBR Layout on January 10, has found that the lateral support provided to keep the structure intact was inadequate.

A source privy to the developments in the investigation told DH, “The reinforcement cage should have been restrained at multiple locations along its height using guy wires (cables that hold a structure in place). But the restraint system anchoring the guy wires to concrete blocks was inadequate. The reinforcement cage was an unstable structure with inadequate lateral restraints and thus collapsed.”

Earlier IISc had been asked to probe the structural flaws and submit a report. But the top rung of the Bengaluru police wanted to bring in an additional independent wing and chose to commission the study to professors at IIT.

The report also stated that the full length of the cage had been assembled with 32mm bars and were tied using binding wires.

“But only four guy wires were used to hold the entire reinforcement cage in place to prevent it from moving sideways. The arrangement in place was such that even a mild disturbance would be enough to send the structure crashing,” the source said.

The source also said that while the material used in the reinforcement was of standard make, the bars had to be tested to see if was of the prescribed standards.

According to the source, the expert team felt the reinforcement cage could crash only when the system used to support it laterally failed.

The source explained, “The cage had been tied at 15 metres, whereas the pier to be built was of 16.48 metres height.”

“No SOP was followed for putting up the lateral supports. There was no proper design for the system used to support the cage. The support provided by the guy wires was such that even if one guy wire snapped, the entire system would collapse,” the source added.

The source said the restraints were not adequate and not designed to check movement of the reinforcement cage. Site engineers had no clue about the guying system and the consequences of inadequate checks to prevent lateral movement of the reinforcement cage, the source added.

There was neither any safety stewards and nor any SOP in place to ensure safety of vehicles passing by in the event of the structure collapsing were, the source said.