An Assessment of Causative Factors of Building Collapse using Physical Analysis Tests: The Case of Oko, Anambra State, Nigeria

Incessant building collapses in Anambra State Nigeria is posing serious challenges to all the stakeholders in the building industry - building consultants, governments, developers, landlords and users. This has evoked great concern to all key players of the building industry. Thus, this study assessed the causative factors of building collapses in one of the cases, a collapsed uncompleted 3-story building which was reported in Oko town, Anambra State, Nigeria. A qualitative methodology involving subsoil and geotechnical investigation and also destructive testing of collapsed structural elements including sandcrete blocks, concrete and reinforcement bars; to establish the subsoil conditions, compressive strength, the yield stress as well as ductility of the reinforcements bars was adopted for this study. The results of the test carried out on the mass concrete, revealed a compressive strength ranging from 1.4N/mm2 to 3.1N/mm2 (standard compressive strength of 25N/mm2), 6” solid block ranging from 0.3N/mm2 to 0.4N/mm2 and 6” hollow block ranging from 0.2N/mm2, (standard strength value of 1.5 N/mm2 for a non-load bearing sandcrete block in accordance to NIS: 587:2007). The tensile stress of the reinforcement bars (12mm and 16mm) ranging from 280.29N/mm2 to 303.91N/mm2 (According to NIS: 117:2004, standard yield stress value of 410N/mm2 and ductility of 12%). The CPT revealed that the subsoil is generally too soft and the fine aggregate (sand) was poor for concreting. The findings suggest that poor foundation structure, inappropriate mix of concrete, the use of substandard materials, inadequate reinforcement and poor project supervision, contributed to the structural failure that lead to the collapse of the building. Therefore, this research recommends that mandatory, periodic or conditional structural integrity assessment of buildings in use and under construction becomes an exclusive preserve of highly qualified construction professionals. Standard organization of Nigeria should be vigilant to ensure that building materials imported into the country conforms to standard requirements especially the reinforcement bars.