Browsing by Author "Silva, Vitor"
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- Earthquake loss estimation for the Kathmandu ValleyPublication . Chaulagain, Hemchandra; Rodrigues, Hugo; Silva, Vitor; Spacone, Enrico; Varum, HumbertoKathmandu Valley is geologically located on lacustrine sediment basin, characterized by a long history of destructive earthquakes. The past events resulted in large structural damage, loss of human life’s and property, and interrupted the social development. In recent years, the earthquake risk in this area has significantly increased due to uncontrolled development, poor construction practices with no earthquake safety provisions, and lack of awareness amongst the general public and government authorities. In this context, this study explores the realistic situation of earthquake losses due to future earthquakes in Kathmandu Valley. To this end, three municipalities: (a) Kathmandu Metropolitan City, (b) Lalitpur Sub-Metropolitan City and (c) Bhaktapur Municipality are selected for a case study. The earthquake loss estimation in the selected municipalities is performed through the combination of seismic hazard, structural vulnerability, and exposure data. Regarding the seismic input, various earthquakes scenario considering four seismic sources in Nepal are adopted. For what concerns the exposure, existing literature describing the construction typologies and data from the recent national census survey of 2011 are employed to estimate ward level distribution of buildings. The economic losses due to the earthquake scenarios are determined using fragility functions. Finally, the ward level distribution of building damage and the corresponding economic losses for each earthquake scenario is obtained using the OpenQuake-engine. The distribution of building damage within the Kathmandu Valley is currently being employed in the development of a shelter model for the region, involving various local authorities and decision makers.
- Evaluation of Analytical Methodologies to Derive Vulnerability FunctionsPublication . Silva, Vitor; Varum, Humberto; Crowley, Helen; Sousa, Romain; Pinho, RuiThe recognition of fragility functions as a fundamental tool in seismic risk assessment has led to the development of more and more complex and elaborate procedures for their computation. Although vulnerability functions have been traditionally produced using observed damage and loss data, more recent studies propose the employment of analytical methodologies as a way to overcome the frequent lack of post-earthquake data. The variation of the structural modelling approaches on the estimation of building capacity has been the target of many studies in the past, however, its influence in the resulting vulnerability model, impact in loss estimations or propagation of the uncertainty to the seismic risk calculations has so far been the object of restricted scrutiny. Hence, in this paper, an extensive study of static and dynamic procedures for estimating the nonlinear response of buildings has been carried out in order to evaluate the impact of the chosen methodology on the resulting vulnerability and risk outputs. Moreover, the computational effort and numerical stability provided by each approach were evaluated and conclusions were obtained regarding which one offers the optimal balance between accuracy and complexity.
- Generation of spectrum-compatible acceleration time history for NepalPublication . Chaulagain, Hemchandra; Rodrigues, Hugo; Varum, Humberto; Silva, Vitor; Gautam, DipendraThe 25 April 2015 Gorkha earthquake in Nepal caused severe structural damage in central Nepal, including the capital city Kathmandu. Both seismic vulnerability analysis of affected buildings and nonlinear time history analysis need increasing time history. However, no adequate records are available in Nepal, thus structural engineering practices follow Indian guidelines. The Nepal building code allows time history analysis along with the seismic coefficient and response spectrum methods, so nonlinear time history analysis can be used to assure adequate seismic safety. To fulfill the gap of recorded accelerograms, we developed artificial acceleration time histories considering the seismic hazard model of Chaulagain et al. (2015). We compared the synthetic accelerograms developed in this study with the records of Gorkha earthquake; the recorded maximum peak ground acceleration during the Gorkha earthquake showed comparable acquaintance only to the peak amplitudes of synthetic accelerograms generated for 300- and 475-year return periods.
- Video transcoding from H.264/AVC to MPEG-2 with reduced computational complexityPublication . Moiron, Sandro; Faria, Sergio; Navarro, António; Silva, Vitor; Assunção, PedroThis paper addresses video transcoding from H.264/AVC into MPEG-2 with reduced complexity and high rate-distortion efficiency. While the overall concept is based on a cascaded decoder-encoder, the novel adaptation methods developed in this work have the advantage of providing very good performance in H.264/AVC to MPEG-2 transcoding. The proposed approach exploits the similarities between the coding tools used in both standards, with the objective of obtaining a computationally efficient transcoder without penalising the signal quality. Fast and efficient methods are devised for conversion of macroblock coding modes and translation of motion information in order to compute the MPEG-2 coding format with a reduced number of operations, by reusing the corresponding data embedded in the incoming H.264/AVC coded stream. In comparison with a cascaded decoder-encoder, the fast transcoder achieves computational complexity savings up to 60% with slightly better peak signal-to-noise ratio (PSNR) at the same bitrate.