In its report, the technical committee formed to probe the collapse of the roof and scaffolding at Mantri Square in Malleswaram, has recommended a review of the structural stability of the entire building. The report stated that the concrete used in the vicinity of the collapse was weak with a low cement content.
A six-member inquiry committee, headed by Bruhat Bengaluru Mahanagara Palike (BBMP) Commissioner Manjunath Prasad, was formed after the cantilever portion of the busy mall collapsed, injuring two people. The mall will remain closed until the committee’s recommendations are implemented.
Submitted to the BBMP on February 2, the report pointed to multiple deficiencies in the construction of the cantilever. However, as the committee had only taken samples for testing from the immediate vicinity of the collapse, they have now recommended a review of the whole structure. “...in view of the present distress and considering the nature of the building, the structural stability of the whole building needs to be examined,” concludes the report.
Low concrete strength
The testing of the samples had revealed that the strength of the concrete was weak or had weakened. While the design strength was 25 megapascals (MPa), the tested concrete was just 15 MPa - a reduction of 40%. Similarly, the density of concrete was 2,100 kg per cubic m, which is comparatively less for normal structural concrete that is usually around 2,400 kg per cubic m.
Moreover, the cement content was found to be 200kg per cubic m, which was “very low”. “The content should be around 300kg per cubic m for a mix design - that is, if fly ash or ground granulated blast-furnace slag is used along with cement. However, none of the documents submitted by the buildings during the planning stage speak of mix design, thereby implying that the cement content should be much higher... this is reflected in the strength of the material,” a member of the group said.
These “structural inadequacies” and increased load – apart from the corrosion of steel bars by water leaking from a tank above – had made the cantilever section unsafe, noted the report. “This section is around a decade old, and we cannot say with certainty if other portions of the building are immune to the problems that led to the collapse of the cantilever section. This is why we believe the entire building must be examined,” said the member.
Mr. Prasad said the report had been submitted to Mantri Developers and their compliance report was awaited. “Any call on reinstating their Occupancy Certificate will be made after receiving the report from Mantri Developers. Their engineers have to certify the stability of the mall,” he said.
A spokesperson for Mantri Developers said they had asked for a review of the report, and are awaiting the final report in a few days.
