POOR CONCRETING MAJOR CAUSE OF BUILDING COLLAPSE - NBRRI
By YINKA KOLAWOLE
Nigerian Building and Road Research Institute (NBRRI) has identified poor concreting as a major cause of collapse of buildings in Nigeria.
In a paper reviewing cases of building collapse recorded in 2011, Director General of NBRRI, Danladi Slim Matawal, noted that the manner of collapse where in most cases the structures and loads came down without prior warning and the deformation movements so fast with no time to evacuate, is an indication of improper concreting.
He further noted that 70 percent, 23.3 percent and 6.7 percent of collapse buildings belong to private, public and corporate organisations, respectively.
Matawal said notwithstanding other factors that may have precipitated the collapse, such as deficiencies of foundations, columns, beams or other structural elements and use of inferior materials, the sudden failure of the structures denoted that there was poor concreting on the various sites.
'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 reveals that coarse aggregate size as large as 40mm may have been used in the batching process.
'In NBRRI investigations, there has been no convincing evidence to suggest that structural designs were lacking though in most of the situations, especially in Lagos and Enugu, it was a risk to the lives of our resource personnel to insist on obtaining these documents.
'Nonetheless, it is important to emphasize that care should be taken not only to ensure that there should be structural designs for each project, but also to request that all ultimate and serviceability limit states are properly checked and complied with.
'Site supervision on construction sites is both a professionally mandatory function as well as a regulatory role. It is very important that site supervision should be taken seriously on all sites. Thus the town planning and/or development control authorities should insist that all mandatory documents necessary for the successful execution of a project are made available before the commencement of construction and that proper supervision machinery is set up on every site.
'In the projects that NBRRI has visited as a result of failures, there were no project sign boards to state name of project, the client, the architects, the structural engineers, and the quantity surveyors. It is therefore very safe to say that there was no supervision which would have corrected anomalous designs and ensure that all design specifications are implemented on site.
'In nature generally, failures could happen due to faulty construction sequence, scaffolding and formwork faults and early striking of formwork, extra-ordinary loads and unexpected failures. Failures can also be due to a combination of reasons of known causes like design faults, foundation incapacities, etc. The issue of faulty construction is noteworthy because so many structures in Nigeria are standing not because they are technically safe but because the block-work, rather than the structural framing, is helping them to stand.
'Apart from huge corporate organisations that employ well-trained professionals to design and supervise their constructions, private individuals and many government departments and arms of government (like local and state governments) don't consult appropriate professionals and where there is design, no supervision is available to ensure that implementation is well done.
'To complicate the situation, town planning and municipal regulatory authorities traditionally endowed with the responsibility of checking all plans before approval for development is approved no longer undertake their roles and development is now haphazard not only resulting in building collapse but also giving rise to many developments without access roads, water supply, sewerage, electricity and vital services.'