4,860 research outputs found
Mechanical characterization of flexible rockfall barriers through a global multi-component analytical framework
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
A weight-based efficiency measure for energy dissipating devices for flexible rockfall barriers
No full textFlexible barriers are essential passive measures which are able to protect human life, structures and infrastructures from rockfall hazards. When a barrier is impacted, a significant portion of energy dissipation is concentrated in targeted components, named brakes, which can be replaced after the rockfall event. Several technologies exist, differing in both constitutive elements and energy dissipation mechanisms, but experimental data are generally restricted by producers. The present paper compares the various technologies thanks a new efficiency index, that is the ratio between the component potentially dissipated energy and its weight. To analyse the effects of the design parameters, four of the most common brakes are analytically modelled. It is shown that the performance of the devices is variable and depends on the working mechanism and the adopted material. In particular, plastic deformation energy dissipation induced by buckling is generally more efficient than the one caused by bending. Finally, a discussion on the force that activates the brake is proposed. The proposed analyses are of paramount importance for the conceptual design of new energy dissipation devices in rockfall risk mitigation structures
A generalized multi-component analytical method to study the performance of a rockfall barrier under a generic impact condition
No full textThe design of rockfall barriers is based on the system’s ability to absorb and dissipate the energy of an impacting block. Although manufacturers have developed different solutions, leading to countless possible onsite installations, the functional components of rockfall barriers remain largely consistent across technologies. In this study, the mechanical behaviour of a generic system is evaluated proposing a global analytical method, derived from the appropriate assembly of its fundamental components. For a given impact energy and position, this model allows estimating the barrier response in terms of maximum deflection of the net, forces in the wire ropes and energy dissipated by dissipating devices, providing an easy-to-use tool for the design. The method is applied to a 1000 kJ rockfall barrier. As real-scale test results are available for centred impacts only, a numerical model was developed to extend the validation to eccentric load cases. Besides being used for design purposes, the model can be utilized in a maintenance plan to assess the most critical components under various impact scenarios
Prediction of residual rockfall risk in presence of net fences according to the position of the impact
No full textResidual risk assessment in presence of structural mitigation measures represents a challenging issue
as the risk in a given time framework, e.g. the annual risk, should be quantified. This presupposes the
knowledge of the frequency-magnitude relationship of the considered geohazard. To lower the risk
below an acceptable threshold, protective measures are often installed. Structural systems have an
inherent failure probability that should be accounted in the computation of the residual risk.
Dealing with rockfall hazard, the present work proposes an enhanced version of a reliability-based
approach to quantify the failure probability of net fences and the residual risk. Net fences are complex
systems, made by assembling several metallic components with different functions. For each system,
the performance is certified by standards tests that presuppose that the impact occurs in the center of
the fence. Previous works by the authors considered the capacity of the barrier being distributed with a
Dirac-delta function at the certified energy absorption capacity. Anyway, the energy absorption
capacity of a net fence varies according to impact position and impacting features.
This paper proposes a new distribution of the resisting capacity of the barrier based on the different
position of the impact thanks to a numerical FEM investigation on a real barrier. An example of
application is included. The proposed method thus allows predicting the risk reduction in presence of
net fences, accounting for the possible rock impacts. The procedure can provide the basics to be
tailored for other geohazards or different structural protective measures
Effects of eccentric impacts and corrosion on the structural behaviour of retaining wire ring nets
No full textAnti-submarine (ASM) ring nets are fundamental components for various passive solutions to mitigate rockfall hazard. While numerical models could accurately assess their performance for all the applications, the modelling of a whole system comprising the net is time-consuming. An analytical model of wire ring nets currently on the market, applicable to the different configurations, can thus represent a profitable tool to investigate the performance of nets used in retaining systems. Currently, for flexible rockfall barriers the whole system structural behaviour is evaluated with real tests impact tests performed in the centre of the system, only, possibly overestimating the system capacity and consequently underestimating the residual risk at installation sites. An analytical model is proposed in this paper with the aim to evaluate the mechanical behaviour of wire ring nets for eccentric impacts too. The model validation is performed using quasi-static experimental punching tests results related to both rigid and flexible boundaries conditions for the centred impact case, while numerical models, realized applying well-established approaches, strengthen the model validation for eccentric impacts. Analyses performed during the barrier design phase and its service life enable to assess the real efficiency of retaining systems
Failure probability of rockfall net fences subjected to ageing: a reliability- based approach for risk reduction
No full textNet fences, or rockfall flexible barriers, are rockfall risk mitigation structures that have an inherent failure probability. Analysing the variability of the phenomenon and the uncertainties associated to the prediction of the trajectories of the potentially falling blocks, the Authors have found that the adoption of non site-specific partial safety factors, as suggested in Italian and Austrian rules and the European Guidelines, would lead to a wide range of failure probabilities. Hence, they have introduced a new approach tailored for any slope that implements a time-integrated reliability-based analysis. All the previously discussed analyses have been performed on new structures, considering a Dirac-delta distribution for the capacity of the barrier. The present contribution deals with the introduction of ageing phenomena (e.g. corrosion of components, untightening of connections, etc) or the activation of the energy dissipating devices into the evaluation of the failure probability of the barrier. Numerical and analytical modelling and recent tests on artificially corroded barrier components have shown an overall reduction of energy dissipation capacity. Based on the assessment of the current state of a net fence, an appropriate distribution that accounts for the reduction of the capacity and the uncertainties in the evaluation of the ageing parameters is introduced, and the effects on the failure probability of the system are quantified. An example of application is included, showing how risk reduction can be efficiently achieved by considering the effective failure probability of the net fence
A model predictive control approach to the load shifting problem in a household equipped with an energy storage unit
No full textThis paper deals with the load shifting problem in a household equipped with smart appliances and an energy storage unit with conversion losses. The problem is faced by establishing an event driven Model Predictive Control framework aiming to meet the real life dynamics of a household and to keep low the impact of the control system on the total electric energy consumption. The proposed approach allows the consumer to minimize the daily energy cost in scenarios characterized by Time of Use tariffs and Demand Side Management, by dynamically evaluating the best time to run of the appliances and the optimal evolution of the battery level of charge. A proper set of realistic simulations validates the proposed approach, showing the relevance of the energy storage unit in the domestic load shifting architecture
Numerical back-analysis of impacted rockfall barriers steel posts: discussion on the effectiveness of the system
No full textFlexible rockfall barriers are effective structures for rockfall risk mitigation, capable to withstand very high impact energies, up to 10000 kJ. The assessment of the barriers is demanded to the appropriate European Assessment Document EAD 340059-00-0106 (EOTA, 2018): it ties the performance to a standard test procedure, in which the net is the only impacted element. Despite this impacting case is representative of the majority of the cases, other impact positions are possible, e.g. on the supporting elements. Hence, the debate on the performance assessment for the rockfall barriers is still open.
The producing company Geobrugg AG has recently conducted experimental tests producing an impact at the midspan of an internal steel post on a 500 kJ rockfall barrier. In this paper, a numerical back-analysis of these tests is performed to analyze the failure mechanisms and to be able to extend the results for different impact positions on the structural element, evaluating the system effectiveness
Francesco Scorza Barcellona o della passione agiografica
No full textL'autrice traccia, sul filo dei ricordi, il profilo scientifico ed umano di Francesco Scorza Barcellona ed introduce gli studi raccolti nel volume.The author traces, on the thread of memories, the scientific and human profile of Francesco Scorza Barcelona and introduces the studies collected in the book
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