17 research outputs found
The strength of concrete in historical bridges
No full textTo assess the performances of existing Reinforced Concrete (RC) bridges, the current structural analyses need the definition of material properties, and in particular of concrete strength. Such parameter is usually measured by means of destructive tests on concrete cores drilled form a bridge, or by means of indirect non-destructive analyses, such as the acoustic techniques or the rebound hammer test. Nevertheless, in several cases, a rough estimation of the compressive strength of concrete is sufficient, without performing any test on the structures. This is the case of some historical RC bridges, which date back to the early ages of last Century and are cur-rently in service in Italy. Accordingly, the strength-for-year curves have been introduced to calculate the aver-age strength (and the percentiles) of a concrete cast in a specific year. They are based on the results of tests performed on concrete cubes, and stored in a database available at the Politecnico di Torino (Italy). The use of the strength-for-year curves improves the effectiveness of the rapid assessment procedures. As a result, the priorities of retrofitting, necessary to mitigate the risks associated with the prolonged service of RC bridges, can be better identified
Analogies in fracture mechanics of concrete, rock and ice
No full textBoth in architecture and arts, the golden ratio has been taken into consideration most exclusively for its geometrical properties. Specifically, among all the proportions, the golden ratio can inspire beauty and aesthetic pleasure. Indeed, it has driven, in an implicit or explicit manner, the construction of buildings for centuries. Nevertheless, as discussed in the present paper, also fracture mechanisms in brittle and quasi-brittle materials call the golden ratio into play. This is the case of fracture energy and fracture toughness, in which the irrational number 1.61803 recurs when the geometrical dimensions vary. This aspect is confirmed by the results of different experimental campaigns performed on concrete and rock beams and ice sheets. In other words, it can be argued that the centrality of the golden ratio for quasi-brittle structures has profound physical meanings, as it can bring together the aesthetic of nature and architecture, and the equilibrium of stress flow in solid bodie
Behaviour of R/C elements in bending and tension: the problem of minimum reinforcement ratio
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Multi-scale tension stiffening approach for the minimum reinforcement of hybrid concrete beams
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A protocol to assess the seismic criticality of existing small concrete dams
No full textDams are critical infrastructures whose failure would entail serious consequences for community safety. Although large dams represent the most dangerous items, small size dams may be critical, as a large number of these constructions are built in the proximity to inhabited zones. Earthquake is one of the hazards that may affect an existing dam. To assess safety and plan investments, dam owners need to create prioritisation sequences of interventions through a protocol considering technical, political and societal aspects. It is presented herein a specific procedure, based on a multi-criteria analysis with a rapid screening survey of the infrastructures, which addresses to classify the seismic criticality of dams considering the effects (in terms of loss of life and property) of a failure scenario subsequent to an earthquake. A protocol is used to define a prioritisation of interventions that mitigate the seismic risk. It has been applied to a group of 9 small concrete dams and 17 fixed weirs, built from 1920 to 1990 in Aosta Valley (Italy). As a result, about 30% of the existing dams, which are more vulnerable than fixed weirs, shows the highest level of seismic criticality, and needs to be retrofitted in accordance with the current standards
