The building, constructed by Dhaka City Corporation (DCC) at Dayaganj in the city, collapsed only a week before it was scheduled to be open to 60 sweeper families.

A five-member team, comprising two professors of Bangladesh University of Engineering and Technology (Buet) including one geo-technologist, one engineer from army, one from Public Works Department and chief conservancy officer of DCC, was formed to look into what exactly caused the disaster.

"Very poor quality concrete was used in the building," said a member of the expert team on condition of anonymity. "Concrete may have weakness to a tolerable extent, but the kind of weakness we found in concrete used in the collapsed building has no match. Quality control on the other hand was absolutely ignored."

Analysis shows that there was no accountability or monitoring in the process of construction work of the building, said committee sources.

The expert team carried out laboratory tests of soil, iron rod and concrete at Buet and has come to a conclusion that use of substandard construction materials had triggered failure of the structure. The committee is expected to submit the report in next one week.

Collapse of buildings, even while under construction, has become a regular phenomenon in the city because of foundation failure or poor quality materials or poor construction work in recent times, said experts.

The expert team is now waiting for complete removal of the building to examine whether there was any foundation subsidence or piling failure in the construction.

Engineers concerned and the contractor became part of corrupt practice instead of maintaining quality in the construction, said a source adding that the local ward commissioner exercised undue power and the contractor manipulated the work.

"The findings show that lack of supervision, fault in design and poor quality building materials caused the disaster," said another member of the expert committee.

Though required by the Building Construction Act of 1952, the DCC defiantly ignored obtaining approval of the building design from Rajdhani Unnayan Kartripakkha (Rajuk).

According to the law, any person or organisation has to obtain approval of design to construct any building in any area within the Rajuk jurisdiction.

The sweeper families have been living on the roof of DCC's Sweeper Colony Market at Dayaganj since May last year when the construction of the new colony building began.

Ripon Das, a resident of the sweepers colony, said the contractor Atiq Ullah's men have been demolishing the collapsed building and two floors are yet to be removed.

"A construction labourer engaged in removing the debris told me that it would take at least one more month to complete the work," he said.

The DCC sweepers alleged that the authorities undermined the lower level employees like them in developing the house that collapsed days after completion.

Immediately after the collapse experts suspected that structural weakness and geo-technical fault were the reasons behind failure of the building.

"Appropriate design, quality construction materials and consistent quality control of construction work are crucial for safety of a building," said a top engineer.

All the columns in the ground floor of the building broke down very strangely almost in a symmetrical manner and the first floor evenly flattened with the ground floor.

Mayor of DCC Sadeque Hossain Khoka following the building collapse said it might be that the contactor did not do piling of the foundation properly and the engineers responsible for the work did not monitor the construction.

"We hope to remove the collapsed building and begin construction of the new one within a month or two," he said at that time.

But wife of Liton Das, one of the 60 families that were expected to live in the newly constructed building, said none from the authorities concerned has so far told them anything about when they would be rehabilitated.

"We have no idea when we will be able to live in the new building," she said.

Chief Conservancy Officer of DCC Maqsudur Rahman Chowdhury said that demolishing and removal of the building is in the last stage.

The new building had two blocks with 30 rooms at each of them. The north block has collapsed. The south block of the building is of same design.