1,721,007 research outputs found
A tale of two bridges: half joint failure and deterioration processes
No full textLoad capacity assessment of deteriorating RC structures is a part of the strategy to avoid dramatic failures. Two cases of bridge collapse related to deteriorated half joints are presented. The structures were geographically distant – the de la Concorde overpass in Canada and the Annone overpass in Italy - but their histories show common features. The paper builds on the information gathered in the forensic investigations to explore the possiblities of load capacity assessment through different levels of data collection and modelling sophistication. Knowledge is gained by the comparison of half joints failure, design and construction errors, visible symptoms of damage, lack of maintenance, interventions carried out without taking care of overall conditions and lack of a bridge management strategy. Both structures were affected by shear design deficiencies. Regarding the deterioration processes, frost damage was the main issue in the North American case, while corrosion was the driving cause of the collapse in the European one. As for specific aspects, the de la Concorde overpass was influenced by the presence of a weakness zone resulting from inappropriate shear reinforcement details, further exacerbated by the poor concrete quality and severe exposure conditions. The structure in Annone was characterized by cracking caused by overloading and corrosion of the half joint reinforcement. The possibility to apply models within the assessment framework is discussed, with a focus on simple models for different levels of analysis
SLABSTRESS: SLAB STructural RESponse for Seismic European Design
No full textThe dataset reports results from the full-scale testing of a two-storey flat slab structure, undertaken in the SlabSTRESS research project; the construction and testing were planned and carried out at the ELSA laboratory of the European Commission’s Joint Research Centre. The dimensions are three bays by two, spans 4.5 and 5 m, slab thickness 0.2 m, interstorey height 3.2 m. Two different longitudinal reinforcement details were considered; welded studs shear reinforcement was provided only in the second floor slab. The testing program included seismic tests for service and ultimate actions, using the pseudo-dynamic technique with virtual walls. To this aim, a building structure was designed with primary walls and the flat slab frame as secondary element. Cyclic loading tests followed up to ultimate drift capacity of the structure. The sequence of tests included strengthening of a set of damaged connections using bolted bars in holes drilled through the slab, followed by cyclic testing to failure. The instrumentation was provided for the global response and the connections with local rotations in the columns and slab; cracking around the columns was measured with through-crack sensors; a measurement system for internal forces and moments was included within the columns. The results show the response with deformations and damage for the different loading conditions up to failure. The results obtained on a full-scale structure extend and confirm the knowledge in the literature, mainly based on isolated connections and/or small-scale samples
Structural modelling of the response of deteriorated rc and psc members: Levels of approximation for model code 2020
No full textThe assessment of reinforced concrete structures affected by deterioration such as reinforcement corrosion involves the use of different models, according to different scientific and technical purposes. The paper presents a framework for structural modelling approaches previously developed by the authors to fit in the concept of Levels of Approximation for Model Code 2020. The concept is here extended to include different accuracy levels in deterioration modelling. The paper moves from simple strut and tie models to analytical models and finite element numerical studies. The possibility of an extension of the framework to modelling the freeze-thaw deterioration is highlighted. The conclusions highlight the available techniques and the needs for research developments
Natural corrosion effects on prestressed beams failure modes
Full text linkResearch carried out on the load-bearing capacity of naturally corroded beams in laboratory tests and existing structures is presented and analysed. Load tests were performed on short span pretensioned beams that experienced corrosion under service loads in two different industrial environments for 25 years. Prestressed beams from a decommissioned bridge after 40 years of service life with chloride attack were tested to failure. Different failure modes are analyzed using non linear finite element (NLFE) modelling and limit state models. Flexural and shear-bond failure are shown and analysed for prestressed beams with shear reinforcement. The results show that flexural failures can be predicted with simple resistance models and an estimate of the maximum cross-section loss. Lab tests show that bond-shear failure must be considered in corroded prestressed beams; these have been analysed by a NLFE model, but models for the bond deterioration and this structural limit state are not yet available
Proceedings of the CACRCS DAYS 2021 - Capacity Assessment of Corroded Reinforced Concrete Structures from Research to Daily Engineering Evaluation
No full textEvaluation of corrosion conditions of reinforced concrete structures exposed to chloride-bearing environment
No full textTo plan the maintenance of reinforced concrete structures, damaged by chloride-induced corro-sion, their corrosion conditions need to be properly assessed and this can be carried out only if there is a deep knowledge of the degradation mechanism. This paper deals with the mechanism of chloride-induced corrosion of steel in concrete, analysing the factors affecting the time to corro-sion initiation and corrosion propagation. Attention will be then focused on studies carried out in recent years at the mCD Concrete Durability lab of Politecnico di Milano, which were aimed at investigating the corrosion rate of carbon steel rebar embedded in concrete exposed to chloride penetration
Experimental evaluation of rebars corrosion in concrete
No full textThe proper evaluation of rebars corrosion rate in concrete can provide reliable data for the evalua-tion and modeling of the structural behavior. Electrochemical methods, used since the years ’70, are based on the perturbation of the free corrosion conditions by means of DC or AC current (or potential): the experience gained in the last decades shows that the most reliable method is the linear polarization resistance, based on small DC polarisation vs the free corrosion potential. Promising results have also been got by the measurement of concrete resistivity in carbonated concrete. AC methods have been largerly used in laboratory, while their application is limited on site. Accelerated corrosion test have been used to simulate in short time a significant reduction of the cross section: the limitations of these methods are briefly discusse
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
Effect of environmental exposure conditions on the corrosion rate of carbon steel bars in carbonated concrete
Full text linkIn urban environments the propagation phase of corrosion can represent a significant part of the entire service life of a reinforced concrete structure. To properly evaluate its duration, the knowledge of the corrosion rate is essential. This paper reports the corrosion rate and corrosion potential of carbon steel bars embedded at different depths (i.e. 10, 25 and 40 mm) in concretes with different binders and water/binder ratio of 0.61, exposed both outdoor in Milan in unshel-tered conditions and in laboratory conditions characterized by different temperatures and relative humidity levels. Concrete resistivity at different depths is also reported. Relative humidity strong-ly influenced the corrosion potential, corrosion rate and resistivity, whilst temperature played an important role only at a high relative humidity level. Correlations between these parameters were analysed and discussed
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