The Nigerian Building and Road Research Institute has linked the collapse of a two-storey building last week in Gwarimpa, Abuja, on a demolition that was not done properly.
NBBRI in its preliminary report on the incidence made available to LEADERSHIP, stated that at the time of visit, the structure had been completely demolished to rubble and that the owner of the building, which is the Nigerian Navy was said to have earmarked this particular building for demolition due to some observed structural defects.
The report indicates that in pursuance the Institute’s mandate, the Nigerian Building and Road Research Institute(NBRRI), convened a site meeting following media report of the collapse of a two-storey (Ground, 1st and 2nd floors) building in which lives were reportedly lost and injuries sustained on Saturday January 28, 2012 in Abuja.
The report reads in part: “The case of this catastrophy of the building at 45 Road, 1st Avenue, Gwarimpa Estate, Abuja, has been established to be; without any ambiguity, as a result of demolishment operations conducted on the site. The operations should have been controlled to minimise or even eliminate risk of injury and to life.
“Under no circumstance should such an operation be haphazardly and unprofessionally undertaken. Demolition exercises of structures all over the world are usually a professionally planned and executed job with special process for every situation.”
The institute also observed that there is clear evidence that the reinforcement for all structural elements (floors, beams and columns) had dissociated from the concrete during demolition. Expert opinion is that this is evidence of poor concreting, i.e. lack of bond between steel and concrete. The inspection also revealed that coarse aggregate size as large as 40mm may have been used on the batching process.
However, specimen concrete samples brought to NBRRI Laboratory and measured using non-destructive testing process gave the following rebound hammer readings: 22, 15, 11, 20, 11, 14, 16, 12, 21, 12 and 14, 10, 10, 9, 8, 7, 6, 9, 9, 10, 9 with an average of 17.5 rebound value and 9 rebound value respectively. Consequently, the compressive strengths of the 2 large-size concrete samples, converted from the rebound values were 8.75N/mm2 and 4.5N/mm2 respectively. The second sample was retrieved from a column concrete.
The preliminiary investigation was conducted by NBBRI in collaboration with Nigerian Society of Engineers, Council for Registration of Enginners in Nigeria (COREN) and the Federal Housing Authority.