1,721,226 research outputs found
Implementation of Steel Constitutive Model Including Buckling in Parc_CL 2.1 Crack Model
Full text linkLacking of details in existing structures, like high value of stirrups spacing, causes a bad confinement of concrete and consequently high lateral deformations of longitudinal bars after the spalling of the concrete in case of cyclic loading induced by seismic actions. Longitudinal reinforcing steel in reinforced concrete (RC) elements may undergo large tension and compression strain reversal that lead to buckling of steel bars. The buckling is a phenomena associated to bar slenderness values that typically may cause second order effects.
In non-linear finite element analysis (NLFEA) rebar can be modelled using beam elements with geometrical and mechanical non linearity or using different approaches like fibre models or smeared models in which the steel behaviour is represented by constitutive model derived on the average behaviour of bare bar experimentally calibrated. In this field it is located the PARC_CL 2.1 smeared crack model implemented at the University of Parma in UMAT.for user subroutine of Abaqus software. Two different models for the buckling effect have been implemented. The first one is the Monti-Nuti model, able to take into account the softening of steel in compression in case of bar slenderness values ranging from 5 to 11. The second one is the Kashani model, for slenderness values up to 30.
In this paper, NLFEA of a RC column is provided to highlight the differences of the response prediction between the two models
Numerical prediction of multi-storey reinforced concrete walls by static and dynamic analysis using the PARC_CL 2.0 crack model
No full textPhase 2 of the CASH benchmark was dedicated to the response prediction of multi-storey reinforced
concrete (RC) walls used as seismic resisting members in nuclear power plants. Nonlinear static and
dynamic analyses have been carried out to check the reliability of non-linear finite element analysis
(NLFEA) to assess the seismic capacity of reinforced concrete walls. Authors attended the benchmark
by modelling RC walls using multi-layered shell elements and by adopting a self implemented crack
model. The paper describes modelling strategies and some critical issues of the Eurocode 8 prescriptions for the shear demand and shear capacity evaluation of multi-storey RC wall
Il Collasso Progressivo e la Robustezza Strutturale nel Quadro Normativo Nazionale e Internazionale
No full textA crack model for corroded reinforced concrete elements subject to cyclic loading
No full textCorrosion of embedded reinforcement is the main cause of deterioration of existing reinforced concrete infrastructure. Corrosion can significantly affect the seismic response and failure mode of reinforced concrete elements, causing premature concrete crushing, size reduction of reinforcement, degradation of mechanical properties of steel and concrete, and degradation and breaking of stirrups. The latter effects trigger inelastic buckling of the longitudinal reinforcement. In this paper, a non-linear finite-element approach, based on multi-layer shell elements and a crack model, is presented. The fixed crack model was developed at the University of Parma (Italy) and is implemented as a subroutine in standard finite-element software. The model incorporates cyclic constitutive laws for steel able to account for buckling of longitudinal rebars and the effects of corrosion. The effectiveness of the proposed model is validated through comparison with experimental data available in the literature. Finally, the capability of the proposed shell modelling to implicitly consider axial force, shear force and bending moment interaction is discussed and comparisons with analytical model and non-linear finite-element analysis results are provided
Service Life Prediction of Corroded Prestressed Concrete Beams based on Probabilistic Assumptions
No full textPrestressed concrete (PC) members are wide used components for bridges, infrastructures, buildings, etc... However, despite its advantages, the structural durability of PC members results to be extremely affected by chloride-induced corrosion deterioration. Based on the probabilistic prediction of the maximum pit depth distribution of prestressing wires, the present work aims to investigate the remaining service life of corroded PC beams. In particular, referring to a determined exposure class, the effects of the chloride attack on prestressing wires are reproduced by considering different corrosion pit penetration depths. The average value of the maximum pit depth distribution, the fractile at 5%, and the fractile at 95%, are assumed, respectively. Finally, the comparison between the analysed configurations is carried out and the main conclusions are drawn
Capacity assessment of existing RC columns taking into account bi-axial shear failure
No full textSeveral scenarios can trigger bi-axial shear in reinforced concrete (RC) vertical members such as wind actions, earthquake, fire, and explosions. In this paper, bi-axial shear scenarios are analysed and the capacity of corroded RC members such as columns or bridge piers is evaluated. Firstly, the interaction between bending moment and shear force, combined with cyclic degradation is analytically evaluated. To this aim, the recent formulation proposed by Biskinis and Fardis for the assessment of the uni-axial shear resistance is extended to plot the bi-axial failure criterion, while the ductility is evaluated by considering the effect of the bi-axial bending moments and the applied axial force. Finally, design provisions are given in order to propose adjustments to the formulations provided by standard Codes and Guidelines that allow to take into account the effect of corrosion in the assessment of the bia-axial shear resistance of RC members
Ultimate chord rotation of corroded reinforced concrete columns subjected to cyclic loading
No full textThe seismic response and the failure mode of reinforced concrete structural elements can be significantly
affected by the detrimental effects induced by corrosion, as cracking, concrete crushing, size
reduction of reinforcement, and degradation of mechanical properties of materials. The aim of this work
is to evaluate the influence of corrosion on the structural response of reinforced concrete columns, using
finite element analysis. A parametric analysis is conducted in order to investigate the dependency of
ultimate chord rotation on the corrosion level of longitudinal reinforcement. Finally, a reductive coefficient,
to be applied to the empirical formulation for the calculation of ultimate chord rotation, is proposed
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
Il fenomeno del buckling implementato nel modello fessurativo PARC_CL 2.1
Full text linkGli edifici esistenti in calcestruzzo armato, progettati prima delle attuali normative sismiche, presentano solitamente un’armatura traversale ridotta o assente che causa un cattivo confinamento dell’armatura longitudinale. Durante il sisma le armature longitudinali possono essere sottoposte ad elevate deformazioni che possono indurre lo svergolamento (“buckling”). Si rende dunque necessario l’utilizzo di un modello costitutivo per l’acciaio capace di simulare realisticamente il fenomeno del buckling. I modello analizzati nel presente lavoro sono quello formulati da Monti-Nuti e da Kashani implementati nel modello fessurativo PARC_CL 2.1. Sono stati quindi analizzati elementi in calcestruzzo armato sottoposti a carichi ciclici con caratteristiche geometriche e meccaniche tipi-che degli edifici costruiti negli anni ’70 (pre normativa sismica), simulandone il comportamento con entrambi i modelli proposti.Reinforced concrete (RC) structures, designed and built before the modern seismic codes, typically present an un-derestimated transversal reinforcement, that causes a bad confinement for the longitudinal rebars. During earthquake, longitudinal reinforcement could be subjected to high deformations inducing buckling. It is therefore necessary using a constitutive model able to realistically simulate the buckling phenomenon. In the present work, the Monti-Nuti model and the Kashani model has been ana-lyzed and implemented in the PARC_CL 2.1 crack model. Then, RC elements subjected to cyclic loads with mechanical and geo-metrical characteristics typical of 70’s buildings in Italy (before seismic codes) have been analyzed with the two proposed models.
Saw-tooth softening model for reinforced concrete structures
No full textThe non-linear behaviour of reinforced concrete structures strongly depends on abrupt cracking phenomena. The crack pattern prediction is fundamental to the reliable assessment of the structure, both at the service and at the ultimate limit states. The Non-linear Finite Element (NLFE) analysis is the common tool to perform these verifications. Unfortunately, the constitutive models for RC material are characterized by softening stress-strain relationships, which involve negative tangent stiffness. Therefore, the incremental-iterative solution procedure often leads to numerical instability and divergence problems, especially when the energy dissipated by cracking and crushing phenomena is little compared with the elastic energy stored in the structure. In this paper, the sequentially linear approach is proposed as an alternative to incremental convergence methods. The robustness and effectiveness of themethod is proved through plane concrete and RC case studie
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