196,091 research outputs found
A rate dependent cohesive model for the analysis of concrete-FRP bonded interfaces under dynamic loadings
No full textReinforced concrete structures, strengthened with fibre-reinforced polymers materials (FRP), are frequently subjected to dynamic loadings, due to, e.g., earthquake, blast, or impact events. The definition of proper cohesive laws to model the bond between the fibre-reinforced polymer sheet and concrete, under high deformation rates, is a crucial issue because the typical failure mode of these joints is debonding of the composite from the concrete substrate. Although numerous studies have already investigated the quasi-static interface response, experimental and numerical investigations, concerning the effect of deformation rate on the bond behaviour between a fibre-reinforced polymer sheet and concrete, are still few. This paper presents a cohesive law for the modelling of interfaces under mixed-mode dynamic loadings, considering the effect of deformation rate. The formulation is based on the decomposition of the discontinuity displacement vector across the interface into elastic and viscoplastic components, with the evolution of the latter being governed by a viscoplastic law formulated according to the overstress approach. Experimental results available in literature, related to double- and single-lap shear tests, performed on FRP reinforced concrete specimens, are exploited to validate the proposed model and to show its capacity to simulate closely the experimental behaviour
A new cohesive law for the simulation of crack propagation under cyclic loading. Application to steel- and concrete-FRP bonded interface
No full textThis paper presents a new cohesive law for modelling interfaces under mixed-mode cyclic loading. The formulation is based on the definition of a free energy function which governs the interface behaviour under monotonic loading, which is then extended to cyclic-driven decohesion through the introduction of a scalar damage variable, whose evolution in time is governed by a phenomenological rate equation. The cohesive model is formulated for a mixed-mode problem and then it is applied for the simulation of debonding phenomena occurring at the interface under a pure a shear stress state. Experimental results available in literature, related to single-lap shear tests, performed on both concrete and steel specimens reinforced by fibre reinforced composite (FRP), are used to validate the proposed model and to show its effectiveness to simulate very closely the observed experimental behaviour
Strengthening of different types of slabs with Composite-Reinforced Mortars (CRM)
Get PDFA great number of buildings built in Europe in the second half of the last century are currently in need of strengthening and retrofitting. One of the more frequent issues is the weakness of the slabs and, in particular, of the intrados covering layer (usually a plaster) and/or of the clay non-structural elements employed to decrease the overall slab weight. The application of composite-reinforced mortar (CRM) systems represents a fast and easy solution to address these weaknesses. Therefore, they are particularly attractive for applications in school buildings, to avoid long interruptions of the educational activities. In this paper, the use of CRM to strengthen different types of slabs is described and discussed on the basis of the results obtained from an experimental campaign conducted at the Politecnico di Milano
Stochastic and recursive estimation of the hygro-thermo-chemical-mechanical parameters of concrete through Monte Carlo analysis and extended Kalman filter
No full textHygro-thermo-chemical-mechanical models, used to determine the variations over time of temperature, relative humidity and shrinkage induced deformations in concrete components, are characterised by the presence of a large number of input parameters. Some of these parameters can be evaluated on the basis of the concrete mix specifications or from literature data, while the others present a large variability and, in some cases, do not have a precise physical meaning and, for this reason, require the implementation of proper identification strategies. The experimental work involved for this characterisation can be time-consuming and costly because based on the long-term monitoring of the time evolution of the field quantities in specific positions within concrete components. The aim of this paper is to propose and validate recursive identification strategies that exploit, in a step by step fashion, the information coming from the experimentation for the identification of the model input parameters. The influence of different exposure conditions and of different concrete thicknesses are investigated and, for each scenario considered, the expected identification error of each parameter is estimated, within a stochastic context implemented through Monte Carlo analyses and Kalman Filter, as a function of the monitored time
Identification of the parameters contained in a cyclic cohesive zone model for fatigue crack propagation
No full textCyclic cohesive zone models provide a useful tool to describe fatigue driven crack propagation,
covering a wide range of engineering applications. For a proper use of these models, particular
attention must be devoted to the correct calibration of the parameters contained, considering that
some of these can be characterized by a large variability and/or by the absence of a precise
physical meaning so that they are not amenable to a direct measurement. This paper proposes a
robust inverse analysis procedure, to investigate the identifiability of the model parameters
governing the fatigue induced damage evolution, in a recently proposed cyclic cohesive zone
model. A novel control for compact test specimens providing more meaningful experimental
information is proposed. The identification problem is formulated by considering fatigue crack
propagation curve and deformations measurements in a discrete number of points of the specimen
surface as input data of the inverse algorithm. The finite element operator, adopted to simulate
the experimental tests, has been substituted by a proper calibrated meta model to reduce the
computational cost of the forward operator and, thus, to solve the inverse problem in a stochastic
context through Monte Carlo like procedures. Representative results, obtained starting from
virtual data affected by different levels of noise, are reported to highlight the identifiability of the
model parameters on the basis of the experimental data adopted. Indications regarding the
minimum number of measurements needed to make the inverse problem well-posed are also
provided, supporting possible planning of measurements setups for laboratory investigations
SHRINKAGE BEHAVIOUR OF COMPOSITE STEEL-CONCRETE FLOORS USING A HYGRO-THERMO-CHEMICAL-MECHANICAL MODEL
No full textComposite steel-concrete structures are widely used throughout the world for different applications. In the case of building systems, composite solutions can be specified and adopted in the form of composite slabs, composite beams and composite columns. Recent research carried out on the service behavior of composite floor systems has pointed out that a non-uniform shrinkage profile develops through the concrete thickness for a slab cast on profiled steel sheeting. These observations are particularly significant when considering that the design of composite floors is commonly governed by serviceability limit state associated with deflection limits. In this context, this paper provides a brief overview of the main factors influencing the service behavior of composite slabs and of a model capable of predicting their long-term deflections by evaluating the non-uniform shrinkage effects by means of hygro-thermochemical-mechanical model. This approach requires the use of an inverse analysis procedure to identify the large number of parameters of the multi-physics model. The results obtained with this refined strategy have been compared with those calculated with a simplified design approach that is available in the literature for the evaluation of the effects produced by non-uniform shrinkage. The adequacy of the proposed prediction model is then outlined by comparing the long-term deflections obtained with both multi-physics and simplified approaches with those measured experimentally from long-term tests carried out on selected post-tensioned composite slab samples that have been reported in the literature
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