The significance of seismic hazard on structural design in Zambia

Abstract

Design and construction practices in Zambia have tended to neglect the risk posed by seismicity on structures, and no earthquake design and construction guides exist. The recent earthquake occurrences suggest that earthquake incidences can no longer be ignored. The research studied the occurrence and significance of earthquakes on the design of structures in Zambia. It advanced the hypothesis that there was sufficient evidence to warrant factoring in the risk posed by seismicity in design and construction practices, and hence the need to develop an earthquake design and construction guide. While Zambia’s location in the interior of the African plate may apparently suggest low seismic risk, the influence of the East Africa rift valley cannot be underestimated. Even with limited history and records of earthquake activity in Zambia and the sub region, there are sufficient records of major earthquakes resulting in damage to structures and even loss of lives. The research methodology included literature review of works related to seismicity in Zambia and the sub-region, analysis of raw earthquake data obtained from earthquake monitoring agencies, review of available seismic reports on Zambia and a questionnaire survey targeted at practicing structural engineers and related professionals. Recorded earthquake events and their physical effects on structures, as well as the prevalent structural design practises amongst engineers in Zambia, were reviewed. The research revealed evidence of physical damage resulting from earthquakes. Seismic hazard analysis predicted significant values of peak ground acceleration (PGA) of up to 0.5 g and 0.7 g for return periods of 475 years and 950 years, respectively. The highest values of PGA were observed in Zone 5 of the study which is around Lake Tanganyika in the northern region of Zambia while the lowest values were observed around western region of Zambia. The research noted that most earthquakes in the catalogue were within a depth of 10km which highlights the potential hazard posed by significantly large earthquakes in the region. The limited seismic consideration prevalent in design practises in Zambia is largely attributed to the lack of an earthquake design guide and the preconceived notion that Zambia and the sub-region have insignificant earthquake activity. It is recommended that the Engineering Institution of Zambia (EIZ) should spearhead development of a seismic design and construction guide for Zambia. Keywords: Earthquake, Seismicity, Structural Design and Construction