Abstract
Malawi is located within the southern branch of the active East African Rift System, where earthquakes of moment magnitude (Mw) 7.0 or greater can occur along major faults. The majority of dwellings in the country are non-engineered unreinforced masonry constructions, built by local artisans with little input from engineers. These constructions are highly vulnerable to seismic events due to poor-quality materials and lack of construction detailing. This study presents a new methodology to assess the seismic fragility curves of typical dwellings located in the Central and Southern Malawi. On-site inspections of buildings are carried out to assess geometrical and structural features of 646 façades, and an experimental campaign is performed to characterise the mechanical properties of local construction materials. The collected data allow the identification of different building typologies in terms of quality of materials and construction techniques. The critical failure modes for each of the inspected façade at their ultimate limit state are evaluated analytically. Damage limit states are defined and adopted to derive simplified Static Push-Over (SPO) curves, transformed into incremental dynamic analysis (IDA) curves by using SPO2IDA. The IDA curves are then used to obtain fragility curves for the specific damage limit states. The fragility curves presented herein are the first to be calculated for these building typologies, based on local data, and unfortunately, they show that buildings in Malawi are far more vulnerable to earthquakes than estimated from previously available international reference data. The fragility curves developed in this study may prove useful for assessing the seismic risk of these building typologies in Malawi and other East African countries.
Highlights
Located in East Africa, the Republic of Malawi is a landlocked country, sharing its borders with Mozambique on the east and southwest, Zambia on the west and northwest, and Tanzania on the north and northeast
This work entails providing an approach capable of assessing the seismic performance and factors affecting structural stability, ductility, and strength of non-engineered unreinforced masonry buildings. There is another important point which should be underlined; fragility curves that are available for Malawi are from international reference sources only and are based on building characteristics inferred from neighbouring countries [e.g. data from Tanzania were used in WHE-Pager classification (Jaiswal et al 2011)]
The match between the bi-linear Sao–Dc and the Static Push-Over (SPO) tri-linear models is based on existing mechanical approaches (Doherty et al 2002; D’Ayala 2005; Derakhshan et al 2014; Lagomarsino 2015), relying on the assumption that masonry walls behave as rigid bodies, which can collapse in In-Plane failure modes or rock in Out-of -Plane failure modes about the pivot points positioned at cracks
Summary
Located in East Africa, the Republic of Malawi is a landlocked country, sharing its borders with Mozambique on the east and southwest, Zambia on the west and northwest, and Tanzania on the north and northeast. This work entails providing an approach capable of assessing the seismic performance and factors (e.g. material quality and structural connections) affecting structural stability, ductility, and strength of non-engineered unreinforced masonry buildings. There is another important point which should be underlined; fragility curves that are available for Malawi are from international reference sources only and are based on building characteristics inferred from neighbouring countries [e.g. data from Tanzania were used in WHE-Pager classification (Jaiswal et al 2011)]. The results provide useful data for the development of structural vulnerability evaluation tools for non-engineered unreinforced masonry structures in Malawi, and the implementation of quantitative risk assessments for East African countries. A summary of statistical analysis of the collected data is presented in Sects. 3.1.1 and 3.1.2 where descriptions of the building typology distributions and of the expected typical failure modes are provided
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