1,720,965 research outputs found
Failure scenarios of small bridges in case of extreme rainstorms
No full textThis contribution comes from the investigations carried out on recent flooding events occurred in
Italian suburban areas. Those events, regarding minor roads, cause unexpected failure modes of
existing bridges with reduced span (less than 10 m), whose construction and maintenance are not
properly covered by standards. Three failure scenarios are here considered: the dragging effect on
vehicles when they are crossing bridges (A), the erosion effect due to the overtopping of the bridge
(B), and the erosion and the floating effect caused by upward buoyant force from Archimedes’
principle on the bridge slab (C). The described mechanisms of failure are paradigmatic to identify
not only the structural collapses but also the service failure. In this sense, the ‘resilience’ of the small
bridge is defined, in view to propose technical indications for maintenance and consolidation
activities
Seismic reinforcement of a R.C. school structure with strength irregularities throughout external bracing walls
No full textThe effect of irregularities due to the non-uniform distribution of material properties on structural elements of a significant real case is here investigated. Mechanical tests performed on a typical Italian reinforced concrete (r.c.) school building built in the 1960s showed irregularity in the distribution of compression strength in columns, even though the construction is featured by substantially symmetric distribution of the frames. Extreme scenarios in the distribution of irregularities in compression strength of concrete columns are analyzed, with the hypothesis of rigid or deformable slabs. The seismic analysis showed the influence of the response due to the irregular distributions of concrete strength. A proposal of equivalent "material eccentricity" is shown to account for the mentioned irregularity. Furthermore, the practical solution of reinforcement to mitigate the effects of irregularities is also described. It consists of couple of external r.c. walls stiffened by r.c. buttresses added to the building, connected by transverse slabs. An extensive reduction of material eccentricity is achieved, together with a relevant improvement in seismic capacity
Estimation of tensile mechanical parameters of existing masonry through the analysis of the collapse of Volterra’s urban walls
Get PDFIn this work, numerical analyses on the Volterra’s ancient walls are performed to understand the causes of a collapse occurred after an extreme rainfall (2014) and to identify the mechanical parameters that most influenced it. The stretch of collapsed wall is modelled with finite elements by distinguishing the material composing the multi-leaf wall. Non-linear static analyses are carried out with the DIANA software considering different levels of hydraulic head up to reach the collapse of the structure. The impact on the failure modes of the involved parameters, such as tensile strength, fracture energy and shear strength, are discussed. Tensile strength is found as the most relevant parameter in the failure mode. Finally, a 3-dim model is presented, and the results show a very good agreement with the failure mode actually occurred in terms of both failure modes and displacement fields. The safety evaluation is performed in the as-built and the retrofitted configuration, consisting in the wall restrained by tie-rods. The results show a significant increasing of the safety level of the retrofitted configuration showing a considerable improvement not only in terms of limit equilibrium but also in terms of structural capacity of the wall
Maintenance interventions period of existing RC motorway viaducts located in moderate/high seismicity zones
Get PDFConsidering the recent collapses which have affected several existing reinforced concrete (RC) motorway bridges, the correct maintenance interventions planning of these strategic infrastructures has acquired increasing importance to maintain a suitable safety level even in case of seismic loads. One of the most important problems which influences the structural performance of existing RC motorway bridges is the presence of corrosion which may affect the bearing-capacity members. In particular, the corrosion of steel reinforcement of the piers due to the carbonation phenomenon is strictly related to the seismic performance of these structures as the viaducts of the Italian motorway networks realized around the 1970s.In this paper, the evaluation of the seismic vulnerability of three existing RC motorway bridges has been developed using non-linear time history analysis. Three corrosion scenarios (slight, moderate and high) have been analysed. The effects of the carbonation, expressed in terms of piers steel rebars area reduction, have been considered as a function of the age of the viaduct. Risk indices calculated as the ratio of the peak ground ac-celeration leading to collapse of the first structural element and the design peak ground acceleration, are useful to optimize the scheduling of the motorway networks maintenance interventions
Structural protection after landslide phenomena : a case study in Northern Italy
Get PDFThe protection of a vehicular road after a landslide due to heavy rainfall is described in this paper. With a vi-sion to design steel barriers and wires, collapse scenarios with simple failure models of single falling blocks are presented. The content refers to an application in a vulnerable area of Northern Italy, where a landslide oc-curred next to an important road. Specific reinforcements and safety features against rolling blocks are illustrated
Climate Change Impact on Corrosion of Reinforced Concrete Bridges and Their Seismic Performance
No full textAs a consequence of climate change impact, a significant variation in terms of temperature, atmospheric humidity, and carbon dioxide concentration levels is happening. This condition leads to several negative effects on the safety and the life cycle of existing concrete structures, such as the increase in the rate of material degradation, due to corrosion phenomena. In fact, the presence of carbonation and corrosion phenomena significantly influence the load-bearing capacity of existing reinforced concrete (RC) structures, under both static and dynamic loads. Among the wide range of existing RC constructions, bridges stand out for their importance. Furthermore, as structures directly exposed to the weather effects, they are more susceptible to these phenomena. In this paper, the influence of corrosion on existing RC motorway viaducts' seismic behavior, considering the impact of climate change, is investigated, by means of an efficient procedure based on the implementation of 3D simplified finite element models and the use of analytical relations to obtain the amount of reduction in the steel reinforcement area as a function of the age of the bridge and of the different corrosion scenarios analyzed. Several scenarios for the expected variations in CO2 concentrations, temperature, and relative humidity are evaluated, considering that most of the viaducts present in the Italian motorway network were built between the 1960s and the 1970s. The results obtained using the projection of climate change impacts are compared with those calculated considering the corrosion scenarios resulting from the DuraCrete research project, to understand if the evolution of climate change leads to worse scenarios than those previously assessed
Modelling of Moisture Effect in Safety Evaluation of Soil-Interacting Masonry Wall Structures
No full textThis paper deals with analytical models of retaining walls interacting with soil, whose mechanical properties are influenced by penetrating moisture. Specifically, urban masonry walls are here considered. The proposed simplified procedure takes rainfalls as the intensity measure dependent on rain duration and return period. Growing levels of imbibition of the soil behind the wall determine a de-crease of the strength parameters of the soil. A geometry of the section at each step of imbibition is analyzed considering a set of soil layers with modified properties over time. The method is applied to a section of the Volterra historical urban walls named "Sperone" which was affected by a relevant collapse occurred in March 2014: a back analysis of the soil-structure section is also proposed to re-place the collapse
Analysis of seismic risk on existing dams. Part I: an example of masonry structure
No full textThe paper deals with the analysis of a gravity masonry dam in Italy. Its mechanical properties are defined by means of experimental tests on the dam and the bedrock. A 3D finite element model was implemented in Abaqus and the analysis suggested by the Italian code for dams was performed. Verifications in terms of stresses, in non-linear range assuming a concrete damaged plasticity model for masonry, were made, showing their compatibility with both tensile and compressive strengths
Analysis of seismic risk on existing dams. Part II: an example of concrete structure
No full textThe paper deals with the analysis of a light-weight gravity concrete dam in Italy. Its mechanical properties are defined by means of experimental tests on the dam and the bedrock. A 3D finite element model was implemented in Strand 7 r.3.4 and the procedure described by the Italian code for dams was performed. Verification in terms of stresses, in non-linear range were made, to assess the structural safety and vulnerability to piping effects
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