Buildings world-wide are one of the most essential assets of humanity, and they serve as a major contributor to the sustainable development of any nation. The consequences of building collapse is usually colossal ranging from loss of lives, damage to property and its attendant socio-economic implications, etc. This menace appears to be worse-off in developing countries like Nigeria where capacity to manage disaster is lacking. Recent incidence of seismic actions in hitherto geographically aseismic zone, has led to advice by researchers to brace up for earthquake in the nearest future. This research attempts to compute the seismic hazard of buildings in Lagos State, a densely populated area of Southern Nigeria. Based on known seismic ground motion for south-western Nigeria, a model is created that estimates the square kilometers of buildings in Lagos that would either collapse or suffer severe damage in case of earthquakes with different intensities. The model used Monte Carlo simulations, drawing random samples from statistical distributions of built area, occupancy levels, construction quality and fragility functions to estimate the number of people who would be affected in terms of bodily harm, loss of domicile or workplace. MATLAB software was used to implement the modeling. Based on the existing construction quality, the result of this research showed a 50% risk of collapse and 30% risk of severe damage to buildings for a moderate earthquake with seismic intensity of 0.4g. This further emphasizes the need for incorporation of seismic consideration in design and improved construction quality in order to reduce the risk of collapse of reinforced concrete buildings in Lagos.
1.1 Background of Study
Apart from insecurity, public ill-health, poverty, and bad governance, another great challenge confronting the global community is disasters. Disasters, both natural and man-made have successfully contributed to hinder the attainment of sustainable development goals agreed by the 193 member countries of the United Nations. The crises emanating from disasters in most developing countries where capacity to manage such is grossly inadequate is not only recurring but also escalating (Egunjobi and Adebayo, 2016). The result has been loss of lives, severe damage to properties and an enormous distortion to national socio-economic and quality of life indices. One notable human induced disaster that has been frequent in occurrence in Nigeria is building collapse which has had a serious threat on the country’s sustainable development (Egunjobi and Adebayo, 2016). Despite being blessed as a nation with the rare occurrence of natural disasters such as earthquakes, Tsunami and Tornadoes, one of Nigeria’s greatest undoing has been the regular occurrence of building collapse. Buildings are valuable resources to humans because they bestow humankind with diverse accommodation in the mould of hospitals, homes, schools, offices, factories, stadia, ports, hotels, etc. Buildings also make available job opportunities for different professions and class of individuals thereby playing a crucial role in the development of nations (Ayodeji, 2011). Buildings enhance sustainable development but in Nigeria this is yet to produce the required results because of numerous building failures (Windapo and Rotimi, 2012). Buildings that are functional increase the national Gross Domestic Product as they meet present needs and also aid in reducing future deficiencies (Brundtland, 1987). Ever since the attainment of independence in 1960, Nigeria has consistently made concerted efforts to increasing the quantity of houses to cater for its ever increasing population. The Nigerian government has actively been involved through huge budgetary and policy provision for the supply of mass housing to its citizens. Unfortunately, as the number of buildings increased over the years so has the number of building collapse. The sites of building collapse dispersed around the entire country are frightening and have made it unthinkable to imagine its effect on the Nigerian economy in general and the building industry in particular. Building failures occurs in diverse forms and significance of which collapse is the worst case. Building collapse is the loss of bearing capacity of a building that results in sudden falling apart of the structure (Falobi, 2009). There are many factors responsible for structural collapse in developing nations; some of these include corruption, poor workmanship, design faults, insufficient supervision, incompetence, greed, poor planning, lack of compliance to building codes, inferior quality of building materials, and limited financial resources (Adeniran, 2013; Ifedolapo, 2015). The consequences of building collapse are also very numerous and palpable to all and sundry, such as such death, disability of collapse victims, loss of time and valuable resources, economic losses, increase in number of homeless people, etc. (Ayodeji, 2011; Oluwatobi, Thang and Olutoge, 2012) Hitherto, Nigeria was believed to be lying in an aseismic zone devoid of earthquake disasters, but recent researches by geologist and seismologist has indicated that the country may actually be vulnerable to earth quake in the nearest future (Afegbua, Yakubu, Akpan, Duncan and Usifoh, 2011). Researchers have proven that fissure zones exist under the area. Taking into cognizance the existence of these fissure zones, the scarcity of seismic information, long term exploration of natural gas and the foundation layout of humongous structures, there is need for the production of a complete seismic ground motion modeling (Adepelumi, Yakubu, Alao, and Adebayo, 2011). This is necessary for site evaluation of seismic risk in low and medium seismic areas. Models that evaluate losses provide governments and other stakeholders with data that are necessary to enhance decision making before and after seismic actions, such as ranking of activities and programs to dampen the effects of seismic hazard. These data could also be necessary in the choice of construction locations and methods (Fernandez, 2014). It is expected that the outcome of this study will mitigate the risk of collapse and other losses during seismic events in Nigeria and will also better prepare Nigeria for the attainment of sustainable development goals through the provision of safe buildings for its residents.