Development of a seismic risk/loss model for Mansehra city, Pakistan

Student: Naveed Ahmad
Supervisors: Dr Helen Crowley, Dr Rui Pinho

ABSTRACT

A seismic risk/loss model is developed herein for Mansehra city, Pakistan. The model is capable of computing the level of seismic risk, economic losses and human losses for the future expected seismicity in the city for any exposure time. The model developed herein is applied to the single storey unreinforced brick masonry (URBM) buildings in the city. The vulnerability of the URBM buildings is assessed using the DBELA methodology. Seismic hazard incorporated in the risk/loss model is obtained using a state-of-the-practice probabilistic seismic hazard methodology and site specific empirical ground motion prediction model (GMPM).

Probabilistic seismic hazard analysis resulted in a peak ground acceleration of 0.25g on the soil site corresponding to the ground motion level having a 10% probability of exceedance in 50 years exposure time and a return period of 475 years. For this level of ground motion, the vulnerability curves obtained using the DBELA tool show that 5% of the total buildings will be expected to completely collapse, 20% will attain heavy damage with 19% of the buildings having out-of-plane failure, and 21% will be left with repairable damages. Only 54% of the buildings will survive without any damage or with minor damage.

On the other hand, for the 50 years exposure time the seismic risk/loss curves show that 2.5% of the total builidngs will collapse, 5.5% will attain heavy damage with all of them having out-of-plane failure, 10% will attain repairable damage with 2.5% having out-of-plane failure, and 82% of the buildings will survive without any damage or with minor damage. Seismic risk/loss curves are presented for the first time in a risk and loss study of an urban area. Both the vulnerability curves and risk/loss curves reported very different results for the same exposure time. The results of the vulnerability curves are conditioned on the ground motion level while the risk/loss curves are unconditional, thus the results obtained from the seismic risk/loss curves are more useful for decision-making. The seismic risk/loss model developed herein can be applied to all types of structures in the city by incorporating their respective vulnerability into the model.

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