Opening angle of loose-snow avalanches

Loose-snow avalanches occur frequently after snow-falls or as long as snowpack evolves in winter.The two relevant points in the signature of this kind of avalanches are: the lack of internal cohesion and the inverted V shape of the avalanche, also known as ‘'pear'' shape. In this research paper, the opening angle of such snow avalanches is investigated. A discrete mechanical model is defined and Mohr-Coulomb yield criterion is considered. Thanks to a graphical solution that considers Mohr's circles, the opening angle is found and its independence from the value of the cohesion is shown

The role of complexity in random element removal in statically indeterminate structures

Modern requirements on constructions impose that proper design strategies must be adopted in order to obtain a robust structure: in this sense, consequence-based design focuses the attention on the structural response to damage. The behavior of statically indeterminate structural systems under damage is non-linear because the load paths intertwine each other, even if each component behaves linearly. As much as the structural complexity increases, the presence of effective ways of carrying the load becomes crucial for the robustness of the struc- tural system under a damage process acting at random on the structure. In addition, the size of the system plays an important role: although tendentially more fragile, large systems are able to redistribute and absorb the effects of damage even with low complexity. The theoretical considerations are applied to a real case: a statically indeterminate truss structure is presented and randomly damaged. The results are discussed and the possibility of using the normalized structural complexity index as a potential metrics for testing the efficacy of alternate load path strategy in structural design is critically debated

Brief communication: Accuracy of the fallen blocks volume-frequency law

De Biagi et al. (2017) have proposed a procedure for building a fallen block volume-frequency law for rockfall phenomenon. The input data are from both the recording of rockfall events and from the survey of fallen block volumes. The epistemic and aleatoric uncertainties present in the approach affect the value of the parameters of the law. It is shown how to quantify the errors due to missed events, to an observation period of finite duration and to a limited set of measured blocks. At the end, the procedure outputs corrective parameters to compute a design volume for rockfall analysis and engineering calculations

Structural behavior of a metallic truss under progressive damage

Modern requirements on constructions impose that proper design strategies must be adopted in order to obtain a robust structure: in this sense, consequence-based design focuses the attention on the structural response to damage. The behavior of statically indeterminate structural systems under damage is nonlinear because the load paths intertwine each other, even if each component behaves linearly. The paper aims both to highlight the behavior of a metallic truss under progressive damage and to define a possible strategy for designing a truss that is able to sustain damage acting at random on one of its elements. Structural complexity is used as a leading parameter. Following the results of a parametric analysis, it emerges that, as much as the Normalized Structural Complexity Index increases, the efficacy of the load paths is spread such that the impact of random damage decreases, making the approach feasible

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

Complexity and robustness of structures against extreme events

Civil structures are designed to support the loads acting on them. At present, the common practitioner considers both ordinary (winds, snow, accidental loads) and extreme events (earthquake, fire), combines the actions in such a way that, once the resistance of the elements is determined, the probability of failure is limited to a prescribed value. The set of events that may interest the structure is known and, therefore, a statistics of the actions is defined a priori. However, other events that are not forecastable may interest the construction. The sources of such events, called “Black Swans” after Taleb, are unknown, as well as their magnitude. For ensuring the integrity of the construction in such situations, which imply large damages, robust measures have to be taken (Chapter 3). Structural engineering is not the only domain in which unexpected events occur. Nature is the realm of contrasts. By means of evolution, living species differentiates, differentiated, in order to survive and reproduce. Various strategies were implemented in order to guarantee a biological robustness. Such mechanisms evoke one fundamental property of systems, the complexity and the connectivity between the components. The interaction between the parts makes the whole system more robust and tolerant to errors and damages (Chapters 1 and 2). Robustness in structures is implemented through classical strategies, which tend to limit the extent of damages through a design based on the consequences (Chapter 4). Being inspired by natural strategies, the idea of complexity in structural engineering is explored. Many issues arise, since a proper definition of this term has not been stated yet (Chapters 5 and 6). The ef- fects of element removal on frame structures, which represent an example of highly connected structural scheme, are investigated. As a result of simple simulations, the trend observed in Nature, which wants the complex systems to be robust to random damages, are spotted in the loaded structural schemes (Chapter 7)

Mechonomics: design thinking for growth and resilience of sociotechnical organizations

In this paper the principal ideas of mechonomics are introduced. Mechonomics is a neologism indicating the possibility of predicting the behaviour of sociotechnical organizations in the complex and interconnected world of the 21st century by means of models borrowed from structural mechanics. In particular, the concepts of growth, resilience and robustness of the organizations are discussed. The analogy with structural and natural systems is shown to be sound and permits to interpret the effects of the size of the organization and of its internal arrangement and collapse of enterprises and institutions. Consequence-based design, as the tool able to tackle with unpredictable stimuli and external effects, is introduced as the only robust philosophy that should pervade design and management of sociotechnical organizations

Effects of Alternate Load Paths in damage evolution and identification in architectural heritage

The conservation of architectural heritage encompasses various aspects of technical sciences. In large buildings, made and further modified in different stages with different materials and techniques, it is difficult to measure the “health” of its structure in a simple way. The monitoring through displacement gauges represents one of the less costly solutions for estimating the evolution of damage in an existing structure: evidence of damage is represented by an increase of displacements. Anyway, due to the nonlinear behavior of large constructions, it is possible that displacements are measured only when the damage is at an advanced stage. In this sense, urgent measures have to be taken for ensure the stability of the construction. A preliminary study of the monitoring system and a good calibration of the threshold displacement values is required in order to limit the uncertainty about the true damage evolution stage. At the end, a full example illustrating the strategy to adopt in monitoring an historical construction is proposed