Showing papers by "Bernardino Chiaia published in 2012"

Hierarchical structures for a robustness-oriented capacity design

Abstract: In this paper, the response of two-dimensional framed structures made of rectangular cells to the sudden removal of columns is studied. A simulation algorithm based on the discrete-element method is employed, where the structural elements are represented by elasto-plastic Euler-Bernoulli beams with elongation-rotation failure threshold. The effect of structural cell slenderness and of topological hierarchy on the dynamic residual strength after damage R1 is investigated. Topologically hierarchical frames have a primary structure made of a few massive elements, while homogeneous frames are made of many thin elements. It is also shown how R1 depends on the activated collapse mechanisms, which are determined by the mechanical hierarchy between beams and columns, i.e., by their relative strength and stiffness. Finally, principles of robustness-oriented capacity design that seem to be in contrast to the conventional antiseismic capacity design are addressed.

Fractal grain distribution in snow avalanche deposits

Abstract: Scale-invariant phenomena are common in nature and fractals represent a suitable mathematical tool to describe them. Snow avalanche flow is made up of a mixture of grains and aggregates (granules) which can be broken or sintered together. The granular properties and interactions are important in understanding how avalanches flow. In this paper a fractal model for describing the grain-size distribution in the deposit of a snow avalanche is formulated by introducing the concept of aggregation probability. Although the model is two-dimensional, an extension to the three-dimensional case is proposed in the conclusions. The cumulative size distribution law is extrapolated from the model, and a physical discussion on fractal parameters is conducted. Finally, an experimental application to a real avalanche event is considered to confirm the predictions of the model and to present an extension to multifractality.

Robustness-oriented design of a panel-based shelter system in critical sites

Abstract: This paper deals with the design and off-site construction of particular buildings for critical and emergency situations (e.g., natural disasters such as hurricanes, landslides, floods, and earthquakes; war sites; and desert areas), in which challenging requirements have to be fulfilled. The panel-based system of the ES-KO corporation, which is a major player in this particular market, is described from both the architectural and the engineering points of view. Beyond the classical advantages of off-site systems (e.g., lightness and ease of assembly, speed of construction, transportation, and modularity), specific capacity-design rules can provide high standards of safety durability and structural robustness. Many of these rules can be found in nature, such as exoskeletons, parallelization, redundancy, and compartmentalization. These design issues are suited to particular situations, such as settlements, strong wind, earthquakes, and explosions, because they exploit particular strategies not commo...

Snowpack effects induced by blasts: experimental measurements vs theoretical formulas.

Abstract: To analyse the response of snowpack to explosives and the induced artificial trigger- ing of avalanches, an experimental campaign has been realized during the Winter 2010 in Montero- saSki resort - Gressoney La Trinite (AO- Italy). Two different explosives have been tested (dynamite and emulsion); 24 charges were separately detonated at different elevations from the snowpack (on the snow surface, at 0.5 m, 1 m, and 0.5 m below the surface). The measurements of the craters dimensions induced by the different blasts in the snowpack have been performed, coupled with the pre and post snowpack survey. In this paper, the correlation between geometry of the craters (maximum and minimum diameter and depth) and blasts (type of explosive, change and elevation) parameters is analysed and the em- pirical formulas usually used to design the shots on the snowpack are tested. From the energy point of view, a comparison between dynamic criteria given by different kinds of explosive, charges and elevation and static one is done to understand the influence of artificial trigger- ing in the snowpack stability. The aim of the paper is to define the critical explosive charge: the best agreement between mass of explosive and detonation height to induce an artificial trigger of avalanches.

Different surveys techniques to assess the snow erosion and deposition at the punta seehore avalanche test site

Abstract: The aim of this paper is to describe the surveys techniques, used at the Seehore avalanche test site located in Aosta Valley (NW Italy), concerning the snow erosion and deposition due to avalanches and the preliminary results obtained during the first operative seasons. The following approaches are used: - the laser scanner technique: the data recorded during two experiments are analyzed in order to assess the influence of the morphology of the test site (slope angle) on deposition. Analytical models (the cohesive-frictional and Pouliquen ones) are applied to explain the correlation between the slope angle and the snow depth in the runout area; - the straw test: this new field test is devised to evaluate the net erosion/deposition processes using a very cheap and quick method based on the number and on the position of plastic straws placed within the snow cover. The test is used in the analysis of the eroded and deposited snow along the avalanche track, in particular close to the obstacle,, which was built in the experimental site and was impacted by the avalanches; - the RAMMS simulations: a comparison between the model outputs and the experimental data is made focusing the attention on the eroded areas and on the deposition zones; - the manual measurements of the snow depth through a probe: they allow the evaluation of the deposition depth and the involved snow volume.

New eco-mechanical index for concrete structures

Abstract: A new eco-mechanical index (EMI) has been introduced with the aim of quantifying the environmental impact of concrete structures. From a general point of view, this indicator represents the amount of carbon dioxide released to produce certain mixtures of pre-established strength and ductility. Both for normal strength and high strength concrete, with and without steel fibers, these mechanical properties are summarised by the work of fracture under tensile actions. If also structural durability has to be taken into account, the maximum crack width of reinforced concrete structures must be computed. This is possible by using a tension-stiffening model, here applied to reinforced concrete elements in tension. However, with or without the evaluation of crack width, the concrete with the best EMI releases the highest fracture energy. For this reason, the work of fracture represents also a durability parameter, and therefore it can be used to tailor cement-based composites with the highest strength, ductility, and durability, and the lowest environmental impact.

A new strategy to reduce the environmental impact of FRC

Abstract: Concrete cylinders are subjected to uniaxial compression tests in order to define the whole mechanical response of different mixtures, including the strength and the post-peak ductility. With respect to traditional concretes, the deleterious effects produced by the reduction of cement content (and thus of dioxide carbon emission) can be mitigated by adding mineral admixtures and/or fibers. For instance, fly ashes and silica fumes can increase the compressive strength, even in the presence of a high water/cement ratio. Similarly, low amounts of steel fibers (less than 1% in volume) can drastically enhance the post-peak toughness. Starting from these experimental observations, a new eco-mechanical index is here introduced with the aim of defining an effective strategy to reduce the environmental impact of concrete, without any mechanical detriment. The theoretical and the experimental analyses here developed seem to confirm that the idea of tailoring a new generation of fiber-reinforced concrete, capable of maintaining high mechanical properties with a reduced amount of cement, is not a chimera

New eco-mechanical index for concrete structures

Abstract: A new eco-mechanical index (EMI) has been introduced with the aim of quantifying the environmental impact of concrete structures. From a general point of view, this indicator represents the amount of carbon dioxide released to produce certain mixtures of pre-established strength and ductility. Both for normal strength and high strength concrete, with and without steel fibers, these mechanical properties are summarised by the work of fracture under tensile actions. If also structural durability has to be taken into account, the maximum crack width of reinforced concrete structures must be computed. This is possible by using a tension-stiffening model, here applied to reinforced concrete elements in tension. However, with or without the evaluation of crack width, the concrete with the best EMI releases the highest fracture energy. For this reason, the work of fracture represents also a durability parameter, and therefore it can be used to tailor cement-based composites with the highest strength, ductility, and durability, and the lowest environmental impact.