Percorrer por autor "Silva, V."
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- Enhanced H.264/AVC video streaming using network-adaptive multiple description codingPublication . Correia, P.; Assunção, P.; Silva, V.This paper presents a network-adaptive multiple description coding (MDC) method for enhanced video streaming over multipath channels. The novel feature of the proposed MDC network adaptation scheme is the generation of a controlled amount of side information to compensate for drift distortion due to packet loss. This yields higher robustness of multiple description (MD) H.264/AVC streams than single description (SD) ones. Multiple Description Scalar Quantisation (MDSQ) is used to split an SD video stream in two complementary streams (two descriptions) for transmission over a multipath channel. The simulation results show that significantly better quality is achieved by using the proposed scheme instead of either SDC streams or classic SDC-MDSQ network adaptation without side information.
- Evaluation of analytical methodologies used to derive vulnerability functionsPublication . Silva, V.; Crowley, H.; Varum, H.; Pinho, R.; Sousa, RomainThe recognition of fragility and vulnerability 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 these 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 approach on the estimation of building capacity has been the target of many studies in the past; however, its influence on the resulting vulnerability model for classes of buildings, the impact in loss estimations or propagation of the uncertainty to the seismic risk calculations has so far been the object of limited scrutiny. In this paper, an extensive study of static and dynamic procedures for estimating the nonlinear response of buildings has been carried out to evaluate the impact of the chosen methodology on the resulting capacity, fragility, vulnerability and risk outputs. Moreover, the computational effort and numerical stability provided by each approach have been evaluated and conclusions drawn regarding the optimal balance between accuracy and complexity. Copyright © 2013 John Wiley & Sons, Ltd.
- Seismic fragility functions for Portuguese RC precast buildingsPublication . Sousa, R.; Batalha, N.; Silva, V.; Rodrigues, H.Fragility functions are fundamental for the assessment of seismic safety of structures or the loss assessment of a portfolio of assets. The present paper describes a procedure to derive fragility functions representative of Portuguese reinforced concrete precast buildings. This goal was achieved following an analytical methodology considering the result of hundreds of nonlinear static analyses, whose building models reflect both mechanical and geometrical characteristics of the Portuguese industrial building stock. Considering the specificities of this typology, and in particular the connections between the structural members, a recently developed macro-element was employed, which enables the explicit simulation of friction and dowel mechanisms. The fragility analyses considered both structural and non-structural limit states, and the findings indicate a poor seismic performance, even under low seismic demand.