1,720,963 research outputs found
Failure analysis of the impact of a falling object on a bridge deck
No full textEven if not explicitly considered in most structural design codes, nor studied in-depth in past literature, reports from all over the world seem to indicate that accidental dropping of large heavy objects from transportation trucks can occur. The impact of such heavy objects onto the deck of a bridge can potentially give rise to the development of internal forces higher than those for which the bridge was designed to. To this end, the assessment of the response of bridges subjected to potential impacts from falling objects should be undertaken through idoneous numerical modelling. In recent years, the Applied Element Method (AEM) has been extensively employed to explicitly model complete structural response from the initial elastic stage all the way up to collapse and ensuing debris distribution. The present study, therefore, explores the capability of the AEM to model impact scenarios on bridge decks. It starts with a validation against experimental data available in the literature, and then passes onto the modelling of a case-study, the Morandi bridge, which at the time of its collapse, in August 2018, was being crossed by a truck carrying a heavy steel coil. However, initially use is also made of simplified analytical expressions available in the literature to estimate the forces generated by an impact of this type, with a view to gain additional confidence and reassurance on the obtained numerical results. A local model of the bridge span that the steel coil could have impacted is first developed to preliminarily assess different potential impact scenarios, followed by the analysis of a full model of the collapsed viaduct, including the estimation of debris distribution
Numerical dynamic characterisation of concrete bridge stays
No full textFollowing the recent collapse of a cable-stayed bridge in Genoa, Italy, an interest has arisen to understand if it would have been possible for unknown localised material deterioration and/or decrease in prestress levels to introduce noticeable changes in the dynamic behaviour of RC stays. As such, in this study we start by reviewing past research work, experimental and analytical, on the effects that prestress level may or may not have on the dynamic response of RC beam elements. We then review also available analytical formulations used to determine the natural frequency of vibration of prestressed beams, and, subsequently, complete the preliminary investigation on the effects of prestress levels, and local damage, through the analysis of finite element models of prestressed beams and stays. The comparison of analytical and numerical estimations with results obtained from an in-situ dynamic characterisation campaign on a RC bridge stay is also undertaken. In the second part of the study, we explicitly consider the Morandi bridge case-study, for which finite element models of the stays alone, as well as of the full bridge, are developed and analysed. The obtained results are then also compared with the observations made in pre-collapse in situ dynamic characterisation endeavours. All results obtained and discussed lead to the conclusion that, most regrettably, dynamic characterisation endeavours do not have the capability of providing insight on possible localised material deterioration or partial reduction of the average state of compression in this type of structural elements
Critical review and modelling of the construction sequence and loading history of the collapsed Morandi bridge
No full textThe Viaduct over the Polcevera River, designed by Riccardo Morandi, was a very strategic and important bridge, built in Genoa (Italy) in the mid-60s. In addition to being a renowned engineering work, due to a very innovative design at that period, the bridge was also considered as one of the symbols of the city. On the 14th of August 2018, however, a portion of this bridge suffered a catastrophic sudden collapse that caused 43 casualties. In order to be able to understand, within the context of the necessary numerical forensic investigations, the stress state to which the bridge was subjected to at the moment of collapse, it is first necessary to reproduce both its construction sequence, as well as the loading history the structure was subjected to throughout its life. This work is thus focussed on such task, as well as on showing the differences between the construction sequence that had been initially envisaged at the design stage and the one that was then actually followed during construction. The analyses carried out highlight how important is the correct modelling of the construction sequence, showing how the use of unknowingly incorrect inputs, may give rise to erroneous stress state estimations, which can then in turn mislead post-collapse forensic studies. In addition, the changes in permanent loading (e.g. addition of asphalt layers, replacement of road barriers) and time-dependent effects (e.g. concrete creep and prestress relaxation) over the course of the 51 years of life of the structure, are also scrutinised and discussed, with a view to try to reproduce as accurately as possible the stress state conditions of the structure at the time of its failure
Failure analysis of ageing RC bridges: the cases of the Polcevera viaduct and the Caprigliola bridge
No full textNumerical Study on the Collapse of the Morandi Bridge
No full textAn innovative discontinuum-based micromodeling approach, the Applied Element Method, is used in this work to investigate explicitly potential failure mechanisms that might have contributed to the collapse of the Morandi Bridge in Genoa, Italy, which occurred on August 14, 2018. While, consistently with the findings presented in a previous contribution by the same authors, the initial trigger of the collapse mechanism was assumed as the release of one of the stays, this study investigates, through a sensitivity study, the impact that several parameters and epistemic uncertainties, including reduction of cables' cross section (potentially induced by corrosion) and various possible configurations of both passive and active reinforcements in the main deck, have on the predicted failure mode. Then, to indicate the structural elements and details in which a potential presence of corrosion should be more carefully explored, the observed debris distribution is compared with its numerical counterparts
Revisione critica e modellazione della sequenza di costruzione del viadotto sul Polcevera
No full textAnalytical and numerical analysis of the torsional response of the multi-cell deck of a collapsed cable-stayed bridge
No full textA relevant portion of the bridge over the Polcevera river in Genoa, widely known as the Morandi bridge, collapsed suddenly in August 2018, causing 43 casualties. While most initial forensic studies indicated that a cable-stay failure likely triggered the bridge collapse, only preliminary modelling of the ensuing flexural-torsional-shear failure of the bridge's deck has been undertaken to date. This paper extends previous work by (i) including the most up-to-date knowledge of the Morandi bridge's as-built geometry and reinforcement, (ii) performing detailed numerical studies of the bridge deck capacity, damage accumulation, failure modes, and reinforcement details, and (iii) comparing advanced numerical results with analytical methods to assess the prediction capabilities of simplified procedures for combined-load scenarios of multi-cell box girders. Concrete damage is numerically assessed with both the Finite Element Method and the Applied Element Method, both of which show damage migration for different reinforcement layouts, knowledge of which evolved throughout the forensic process. A numerical simulation of the failure kinematics is then compared against a frame-by-frame video recording of the collapse and a strong match is observed. Finally, a comparison between numerical strength predictions and analytical strength predictions shows that, even though the analytical procedures require significant simplification of the problem, they produce reasonable strength estimates when compared with the Finite Element approach
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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