Enhancing structural robustness by complexity maximisation

Structural robustness is considered a fundamental prerequisite in the design of structures. In particular, attention has to be paid to events that are unforecastable and with no known magnitude. Referring to an idea by Donald Rumsfeld, these are unknown unknowns. Among all the possible strategies for ensuring robustness, alternating the load paths on the structures may represent a feasible design solution. Structural complexity is a novel metrics for measuring the amount of interaction between hypothetical load paths on a structure. Maximum complexity corresponds to maximum interaction. In the paper, the links between structural complexity and robustness are investigated

Archetypal Use of Artificial Intelligence for Bridge Structural Monitoring

Structural monitoring is a research topic that is receiving more and more attention, especially in light of the fact that a large part our infrastructural heritage was built in the Sixties and is aging and approaching the end of its design working life. The detection of damage is usually performed through artificial intelligence techniques. In contrast, tools for the localization and the estimation of the extent of the damage are limited, mainly due to the complete datasets of damages needed for training the system. The proposed approach consists in numerically generating datasets of damaged structures on the basis of random variables representing the actions and the possible damages. Neural networks were trained to perform the main structural monitoring tasks: damage detection, localization, and estimation. The artificial intelligence tool interpreted the measurements on a real structure. To simulate real measurements more accurately, noise was added to the synthetic dataset. The results indicate that the accuracy of the measurement devices plays a relevant role in the quality of the monitoring

An Efficient Reliability-based Design Approach to Reduce Rockfall Risk Below a Target Threshold

Rockfalls are expected to increase due to global warming and extreme events induced by climate change. An accurate quantification of the risk is fundamental for Administrations to predispose effective risk mitigation plans. Risk value should account for all the possible events that can occur in a specific time, i.e. for a magnitude (block volume) frequency relationship. Among structural protective measures, rockfall barriers are widely selected. Despite their design method has been almost defined, even not standardized, the widely adopted safety factors approach with fixed factors does not allow obtaining a specific probability of failure. Moreover, the event magnitude-frequency relationship is not accounted. A novel time- independent reliability-based approach has been recently conceived by the Authors, allowing obtaining the design values for a specific failure probability. The method accounts for all the possible events, integrating them in time with their probability. In this way, an increase of rockfall events can been accurately considered. The obtained barrier failure probability can be used to compute the risk reduction in a given time or, conversely, to define the maximum failure probability of a barrier that could be accepted

A simplified method for assessing the response of RC frame structures to sudden column removal

Column loss is a type of damage that can occur in frame structures subjected to explosions or impacts. The response of such structures largely depends on the capacity of the assembly of elements and on the inertia effects due to the sudden nature of the phenomenon. Frame structures are able to develop various resisting mechanisms that prevent the collapse to progress. The assessment of the robustness often requires complex and detailed numerical modelling. For the preliminary design of a robust frame, simplified methods to assess the effectiveness of the redistribution of the loads after the removal of a member are welcome. In the present paper, an approach based on the idealisation of the damaged structure into a single degree-of-freedom system with an elastic-plastic compliance law is proposed. The output of the method is the dynamic response of a target point, which can serve for assessing the residual safety of the structure. Comparing the obtained results with the outputs of a more sophisticated FE (Finite Elements) analysis, a satisfying accuracy is found

Experimental studies on the progressive collapse of building structures: A review and discussion on dynamic column removal techniques

Dynamic progressive collapse tests are becoming more and more popular in recent years since this approach captures the real structural behavior more robustly, and progressive collapse response more accurately. The results of dynamic tests are of great importance for defining computational models and improving current codes and guidelines. Even for static tests and simulations, the dynamic effects should be indirectly considered, namely by including the dynamic amplification factors. The adopted dynamic column removal approach is the most important and challenging aspect of the dynamic progressive collapse tests. While several methods for dynamic column removal have already been suggested and implemented, a comprehensive discussion of the techniques is missing. In this regard, a comprehensive review of the available literature is first presented. Current experimental techniques for dynamic column removal are categorized into three main groups, i.e., quick-release device, dummy column, and explosion technique, and the underlying concepts and applied methodologies are compared and contrasted. Finally, future needs are highlighted and possible improvements for the current methodologies are also discussed

A mixed quantitative approach to evaluate rockfall risk and the maximum allowable traffic on road infrastructure

Rockfall events constitute one of the most dangerous phenomena in mountainous areas, which can affect transportation routes. In a risk mitigation perspective, the quantification of the risk for pedestrians and vehicles represents a crucial aspect for authorities. A method tailored to these elements at risk is herein presented. The proposed method is based on a mixed formulation of the Quantitative Risk Assessment and the Event Tree Analysis approaches. According to these procedures, an accurate evaluation of the annual probability of adverse outcomes can be computed considering all the scenarios which can lead to a fatality or to an injury. Vice versa, the method lets to evaluate the allowable traffic condition, given an acceptable threshold for the risk. Furthermore, it serves to quantify the risk reduction in case of installed passive mitigation measures and, thus, to plan the priority of intervention works. An application on a study case in the Italian Alps illustrates the potentialities of the methodology

Successful grafting of isolated molecular Cr7Ni rings on Au(111) surface

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Snow Avalanche Impact Measurements at the Seehore Test Site in Aosta Valley (NW Italian Alps)

In full-scale snow avalanche test sites, structures such as pylons, plates, or dams have been used to measure impact forces and pressures from avalanches. Impact pressures are of extreme importance when dealing with issues such as hazard mapping and the design of buildings exposed to avalanches. In this paper, we present the force measurements recorded for five selected avalanches that occurred at the Seehore test site in Aosta Valley (NW Italian Alps). The five avalanches were small to medium-sized and cover a wide range in terms of snow characteristics and flow dynamics. Our aim was to analyze the force and pressure measurements with respect to the avalanche characteristics. We measured pressures in the range of 2 to 30 kPa. Though without exhaustive measurements of the avalanche flows, we found indications of different flow regimes. For example, we could appreciate some differences in the vertical profile of the pressures recorded for wet dense avalanches and powder ones. Being aware of the fact that more complete measurements are necessary to fully describe the avalanche flows, we think that the data of the five avalanches triggered at the Seehore test site might add some useful information to the ongoing scientific discussion on avalanche flow regimes and impact pressure

A new experimental snow avalanche test site at Seehore peak in Aosta Valley (NW Italian Alps) - Part II: Engineering aspects

The estimate of the effects produced by the impact of a snow avalanche against an obstacle is of the utmost importance in designing safe mountain constructions. For this purpose, an ad-hoc instrumented obstacle was designed and built in order to measure impact forces of small and medium snow avalanches at Seehore peak (NW Italian Alps). The structural design had to consider several specific and unusual demands dictated by the difficult environment. In this article, the new test facility is described from the engineering point of view, discussing the most important aspects of the analyzed problems which were solved before and after the construction. The performance of the instrumented obstacle in the first two operating seasons, and some proposals for future upgrading are eventually illustrate