Seismic risk assessment of adobe dwellings

Student: Sabino Nicola Tarque Ruiz
Supervisors: Dr. Helen Crowley, Dr. Humberto Varum, Dr. Rui Pinho

ABSTRACT

Adobe buildings are highly vulnerable in earthquakes. It is painfully evident that each time a strong earthquake strikes in areas where earthen building is common, there is widespread damage to earthen historical monuments and housing and tragic loss of life due to the collapse of these constructions. Recently, this has been seen in Pisco city (Peru) during the earthquake of Mw = 8.0 on August 17, 2007, where more than 500 people died and more than 37 500 dwellings collapsed, where the majority of them were constructed in adobe.

In this research, the seismic risk of non-engineered adobe dwellings located in Cusco (Peru) is studied based on mechanical procedures. The analysis takes into account both in-plane and out-of-plane failure mechanisms of adobe walls. The capacity of each dwelling has been expressed as a function of its displacement capacity and period of vibration, and has been evaluated for different limit states. A probabilistic seismic hazard assessment for Cusco has been carried out to obtain displacement response spectra for different return periods. Finally, from the comparison of the capacity with the demand, probabilities of failure have been obtained for different return periods. These can be expressed in terms of conditional or unconditional seismic risk. The first takes into account fragility curves as function of PGA values, while the second one takes into account many possible future earthquake scenarios that could impact upon urban areas during a given exposure time window.

For example, the conditional seismic risk and for an event with PGA= 0.18g, it is expected that 77% of the adobe buildings can collapse or be near collapse because of insufficient in-plane capacity. Considering the out-of-plane capacity, it is expected that around 75% of the buildings would have wide vertical cracks at the intersections between walls, which could result in the partial collapse of those buildings. For the unconditional seismic risk, ratios of damage of exceedance have been calculated for different time windows, which can help to convey the message of risk to the public and to decision makers. These results indicate the necessity of improving the seismic capacity of adobe dwellings by providing reinforcement, which is capable of guaranteeing ductility and integrity of the adobe walls

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