ANÁLISE DINÂMICA E VERIFICAÇÃO À FADIGA DOS VIADUTOS DE ACESSO DA NOVA PONTE FERROVIÁRIA SOBRE O RIO SADO

As pontes ferroviárias são estruturas que estão sujeitas a um grande número de carregamentos repetitivos que podem gerar efeitos dinâmicos de valores significativos. Esses carregamentos podem ser responsáveis pelo aumento do dano de fadiga, especialmente nas pontes metálicas, causando a iniciação e a propagação de fendas. Atualmente, a aplicação de metodologias que consideram a interação trem-estrutura assume uma importância crescente, evido ao aumento da velocidade de circulação dos trens de passageiros. Neste artigo são valiados o comportamento à fadiga e a resposta dinâmica dos viadutos de acesso da nova ponte ferroviária sobre o Rio Sado, em Portugal. A resposta nos detalhes críticos é obtida através de modelos de elementos finitos desenvolvidos com técnicas usuais de discretização no software ANSYS, e com recurso a análises dinâmicas com interação trem-estrutura realizadas no software TBI. A resposta numérica obtida é utilizada para avaliação da fadiga

Experimental evaluation of the usage of ad hoc networks as stubs for multiservice networks

This paper describes an experimental evaluation of a multiservice ad hoc network, aimed to be interconnected with an infrastructure, operator-managed network. This network supports the efficient delivery of services, unicast and multicast, legacy and multimedia, to users connected in the ad hoc network. It contains the following functionalities: routing and delivery of unicast and multicast services; distributed QoS mechanisms to support service differentiation and resource control responsive to node mobility; security, charging, and rewarding mechanisms to ensure the correct behaviour of the users in the ad hoc network. This paper experimentally evaluates the performance of multiple mechanisms, and the influence and performance penalty introduced in the network, with the incremental inclusion of new functionalities. The performance results obtained in the different real scenarios may question the real usage of ad-hoc networks for more than a minimal number of hops with such a large number of functionalities deployed

A new inverse analysis approach for predicting the fracture mode I parameters of fibre reinforced concrete

This paper describes the development of a new inverse analysis approach to derive the fracture mode I parameters of fibre reinforced concrete (FRC) by using the experimental data obtained from three-point notched beam bending tests (3PNBBT) and round panel tests supported on three points (RPT-3PS). The approach is based on a global fitting strategy, in which the numerical response is simulated by means of analytical models, and fitted to the experimental results by modifying the variables that govern the tensile behaviour of FRC. The fitting procedure relies on a bounded multi-variable nonlinear least squares fitting algorithm, coupled with an automatic updating procedure of the input parameters based on the force deviation error between numerical and experimental results. The performance and predictive potential of the proposed approach are assessed by means of experimental results from 3PNBBT and RPT-3PS retrieved from the literature. Also, the robustness of the implemented methodology is also investigated by evaluating the impact of the initial guess of the input variables in the derived fracture parameters. Finally, the developed tool is applied within the context of the analysis of a real-scale FRC beam, where the mode I fracture parameters were derived using the newly proposed methodology.The first author acknowledges the financial support provided by Fundação para Ciência e Tecnologia (FCT), Portugal through the grant PD/BD/135174/2017. The FCT, Portugal support from the project POCI-01-0145-FEDER-027990 (PTDC/ECI-CON/27990/2017) is also acknowledged

Two-dimensional integrated mixed-mode smeared crack model for simulating FRC structures

This paper describes the implementation and assessment of the predictive performance of a two dimensional mixed-mode fracture smeared crack model (MMFSCM) in a finite element method (FEM) based software. The referred constitutive model is based on the integration of the aggregate interlock and fibre pullout resisting mechanisms to simulate the behaviour of Fibre Reinforced Concrete (FRC) in both fracture mode I and II. The models used to simulate the contribution of each resisting mechanism predict the normal and shear stresses at the crack level based on the crack opening and sliding displacements. For this purpose, two aggregate interlock models and three fibre pullout models are used. The appraisal of this approach is conducted by simulating two numerical case studies consisting of a three-point notched beam bending test (3PNBBT) for assessing the structural behaviour in mode I, and shear panel tests to appraise the predictive performance of the model in mode II. In addition, modifications to the original formulation of the fibre pullout models are proposed, and a multi-linear branch model is also developed and implemented in order to facilitate the use of inverse analysis tools for defining the mode I behaviour. The numerical simulations have predicted with good accuracy the experimental responses, both in mode I and mode II, capturing not only the peak loads but also the evolution trend of the post-peak responses of the analysed scenarios. The modifications proposed to the fibre pullout models enhanced the overall predictive performance of the MMFSCM. The multi-linear branch model exhibited excellent performance, capturing the experimental response with very good accuracy in all 3PNBBT simulations.The first author acknowledges the financial support provided by Fundação para Ciência e Tecnologia (FCT), Portugal through the grants PD/BD/135174/2017 and COVID/BD/151997/2021. Additionally, the authors thank Cristina Frazão and Inês Costa from CiviTest for providing part of the experimental results used in this study. The authors also acknowledge the support provided by FemWebAI project, Portugal, with reference PTDC/ECI-EST/6300/2020, supported by FCT