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Construction method and numerical approach for the robustness of precast concrete buildings
No full textThe structural robustness of reinforced concrete buildings subjected to accidental actions is nowadays a
relevant research topic in the engineering community. During the years, considerable work was aimed
to the evaluation of the structural robustness of monolithic reinforced concrete buildings, with scarce
attention to precast concrete systems. In this context, the building may be able to withstand the gravity
loads after the loss of a load-bearing element, such as a column, through the role played by the tying
reinforcement, as stated in the current Eurocodes and Unified Facilities Criteria guidelines. In this paper,
a simplified numerical approach is described considering both mechanical and geometrical
nonlinearities for the structural robustness assessment of precast concrete buildings. Nonlinear static
and dynamic responses of precast concrete frames with dry beam-to-column connections are validated
against available experimental tests in the current literature. Finally, practical suggestions and future
requirements are discussed aimed to improve the structural robustness of precast concrete system
Simplified analytical method for moment-curvature response of corroded prestressed concrete beams
No full textNowadays, the corrosion phenomenon is recognized as one of the main causes of
deterioration of reinforced and prestressed concrete (PC) structures. Several experimental and
numerical investigations have been proposed in the literature for the flexural and shear response
of reinforced concrete structures. However, the lack of simplified yet accurate analytical models
have been outlined, especially concerning the residual mechanical response of corroded pre stressed concrete members. To this aim, the present work focuses on the proposal of a simplified
analytical model for the flexural resistance of prestressed concrete beams - subjected to chloride induced corrosion - in terms of moment-curvature response. Firstly, the basic assumptions of the
approach and the validation against un-corroded PC beams are described by adopting a novel
stress-strain relationship for corroded strands previously proposed by the authors. Secondly, the
effect of the corrosion level on the moment-curvature response of deteriorated PC beams is in vestigated. Finally, outcomes are provided concerning: (i) the expected flexural failure mode, (ii)
the evaluation of useful parameters for the assessment of flexural and shear resistances - the latter
referring to the current formulation provided in the Model Code 201
Study of Biaxial Shear Failure Envelope of Reinforced Concrete Columns
No full textSeveral scenarios can trigger bi-axial shear in reinforced concrete (RC) vertical members such as wind actions, earthquake, column loss induced by explosions and/or impacts. The majority of standard codes impose uniaxial shear verification of vertical members and neglect the interaction between shear forces and bending moments acting along the two principal directions of inertia of the transversal cross section. Moreover, bi-axial shear interaction curves proposed by codes are based on the fitting of experimental data conducted on heavily reinforced specimens. In this paper, the bi-axial shear failure envelope of existing RC columns, is investigated. A database previously published by Authors on experimental data on beams and columns tested under bi-axial loading is updated. Afterwards, the experimental shear resistances of the database's members subjected to both monotonic and cyclic loading are compared with analytical predictions. Three different formulations are adopted for the analytical calculation of the uniaxial shear resistance: (i) Model Code 2010, (ii) Eurocode 8 and (iii) the cyclic shear resistance recently proposed by Biskinis and Fardis. Such resistances are adopted to create the bi-axial shear failure envelope. Finally, the shape of the bi-axial shear failure envelope is critically analysed in order to select the formulation that provides the best fitting between experimental and analytical bi-axial shear resistances
SCPS-model Validation Based on a Database of Naturally Corroded Prestressing Strands
No full textChloride-induced corrosion of prestressed concrete (PC) structures is worldwide recognized as a one of the main causes triggering the structural performance reduction of PC members over time. To ac-count for this issue, the accurate estimation of the mechanical properties decay of corroded prestressing reinforcement plays a crucial role. To provide model uncertainties estimation useful for reliable assess-ment of corroded PC members, the paper presents a further validation of the novel SCPS-model, based on an updated test database on naturally corroded strands collected by Authors from scientific literature. As revealed by the statistical analysis outcomes, the SCPS-model is confirmed as a useful tool for the daily engineering practice for the prediction of the residual tensile response of corroded strand
Pushover analysis of reinforced concrete framed structures: comparison between response obtained using beam or multi-layered shell elements
No full textIn the context of the seismic vulnerability assessment of existing reinforced concrete buildings, the load-carrying capacity of structures is strongly affected by steel and concrete mechanical properties and construction details. In this work, the institute “A. De Gasperi – R. Battaglia”, located in Norcia, is chosen as case study. Two different modelling strategies have been adopted by using beam elements or multi-layered shell elements for the structural schematization. The non-linear behavior and the ductile or brittle failure mode of shell elements are evaluated using PARC_CL 2.0 crack model, implemented as user subroutine in Abaqus Code. The non-linear ductile behavior of beam elements is evaluated using, at each integration point, the moment/curvature and the axial force/strain relationships which are uncoupled. Brittle failure mode in columns, beams and beam-to-column joints are calculated using post-processing procedures based on analytical formulations provided by Italian NCT 2018 and Eurocode 8 Standard Code. The main scope of this paper is thus the evaluation of the structural response of the case study by using nonlinear finite element analyses, highlighting the benefits of using beam or shell element modelin
Role of floor diaphragms on the seismic response of reinforced concrete frames
Full text linkIn existing Reinforced Concrete (RC) framed buildings, floor structural components (i.e. RC topping and joists) may play a crucial role in the seismic performance of the structure. The interaction between floor diaphragms and seismic-resistant frames can lead to different effects, depending on the relative stiffness and resistance of the elements belonging to the structures and on the adopted construction details. In this work, these aspects are deepened with reference to the institute “A. De Gasperi – R. Battaglia”, located in Norcia, Italy, chosen as case study. The seismic response of the building is investigated through pushover analyses by adopting a multi-layered shell element approach, where the mechanical nonlinearity is evaluated by using the PARC_CL 2.1 crack model, implemented as user subroutine in Abaqus FE package. The obtained results highlight that the modelling of the diaphragm increases the flexural capacity of the beams, so determining an increase of the seismic global response for frames characterized by ductile failure modes. The modelling of diaphragms may also alter beam-column strength hierarchy and stresses’ magnitude in beam-to-column joints, leading to anticipated brittle failures, that cannot be detected through the modelling of the bare fram
LONG-TERM AND CORROSION EFFECTS ON THE PUNCHING SHEAR RESISTANCE OF RC FLAT SLABS SUBJECTED TO SUDDEN COLUMN LOSS
No full textDuring an extreme event occurring on a reinforced concrete structure, characterized by the loss of a load-bearing element, the remaining resisting members may develop alternate load paths to resist gravity loads. However, it is recognized that reinforced concrete flat slabs are prone to punching shear failure. This issue is particularly relevant for existing reinforced concrete structures where creep, shrinkage, and corrosion effects due to environmental conditions play a fundamental role before the occurrence of the extreme event. In this paper, nonlinear pushdown and dynamic analyses were performed on an existing continuous reinforced concrete flat slab to investigate the structural response in the case of an interior column loss. Firstly, the flexural and membrane action resisting contributions were in-deeply analyzed. Secondly, the crucial effects of creep, shrinkage and corrosion on the dynamic response and punching shear resistance of the system were critically evaluated. Finally, useful insights for the structural robustness assessment of existing RC structures subjected to material deterioration were provided
Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal
No full text: Robustness of reinforced concrete (RC) structures is an ongoing challenging research topic
in the engineering community. During an extreme event, the loss of vertical load-bearing elements can
activate large-deformation resisting mechanisms such as membrane and catenary actions in beams
and floor slabs of cast-in-situ RC buildings to resist gravity loads. However, few studies have been
conducted for precast concrete (PC) buildings, especially focused on the capacity of such structures to
withstand column loss scenarios, which mainly relies on connection strength. Additional resistance
resource and alternate load paths could be reached via tying systems. In this paper, the progressive
collapse resistance of a PC frame building is analyzed by means of nonlinear dynamic finite element
analyses focusing on the fundamental roles played by beam-to-column connection strength and tying
reinforcement. A simplified modelling approach is illustrated in order to investigate the response of
such a structural typology to a number of sudden column-removal scenarios. The relative simplicity
of the modelling technique is considered useful for engineering practice, providing new input for
further research in this field
Robustness-oriented conceptual design of precast concrete frame structures
No full textOngoing research on structural robustness of precast concrete (PC) structures is a source of debate in the structural engineering community because few studies are currently available in the literature exploring it thoroughly. The importance of preventing progressive collapse of such structures relies upon redistribution capacity of structural members through connections and tying systems. A recent study has demonstrated that continuous ties along members can substantially improve the progressive collapse performance of PC buildings. In this paper, quantitative data from nonlinear dynamic analyses of a frame structure under peripheral column removal at different floors is processed to identify the most demanding scenarios. Furthermore, the dependency of the robustness assessment on the ties’ mechanical properties has been investigated both in terms of resistance and ductility. Finally, some remarks concerning the design of key elements, such as columns placed at the corner of the building, are given. The study is aimed at driving the conceptual design of PC frame structures towards robust solutions able to mitigate the risk of progressive collapse under extreme events
A robustness-oriented procedure for the design of tying reinforcement in precast concrete hollow-core floors
Full text linkBuildings may be subjected during their service life to extreme events which can trigger progressive collapse. On this front, the role played by tying reinforcement in structural members is crucial for an adequate load redistribution and the avoidance of disproportionate collapse. This work proposes a robustness-oriented procedure for the design of tying reinforcement placed in the hollow-core units and beams of precast concrete buildings, where limited studies are available in scientific literature. In particular, the aim is to provide a simple yet reliable approach for the design of concentrated and distributed ties in precast floors by adopting fundamental input parameters such as the system’s chord rotation capacity and dynamic amplification factor, which are not considered in current design codes. Firstly, a flow-chart of the design procedure is proposed and discussed. Secondly, the input parameters are calculated based on recent analytical approaches - proposed by some of the authors - to optimize the tying reinforcement design. Finally, the efficiency of the design procedure is demonstrated with an application example, and a novel detailing scheme is proposed which is aimed at a significant enhancement of structural robustness. Due to its simplicity, the proposed design procedure is contended to be applicable in robustness assessment and design of building structures with precast concrete hollow-core floors
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