The paper presents the results of flexural and shear tests up to failure on full-scale hollow-core slabs (HCS) having a depth of 500 mm. A detailed non-linear 2D finite element model is also ...developed to predict the stress distribution and crack pattern within the slabs, providing a well match with experimental results. Experimental and numerical results are compared with analytical calculations provided by Product Standard EN 1168, highlighting the inaccuracy of technical regulations in predicting shear behavior. The proposed numerical procedure is instead viable and sound for the design and the strength assessment of HCS, and can be extended easily to the analysis of whole floor systems.
•Revision of concrete modeling, based on non-linear elasticity, in 2D-PARC relation.•Modeling of dilatation and crushing of concrete under compressive loads.•Extension of the followed approach to the ...case of fiber reinforced concrete.•Implementation of the constitutive model to perform NLFE analyses.•Model validation: comparison between experimental and numerical results.
In this work, a consistent formulation for the representation of concrete behavior before and after cracking is implemented into a constitutive model for the analysis of reinforced concrete structures. This formulation, based on non-linear elasticity, is particularly attractive since concrete stiffness matrix is expressed as a function of only two parameters, namely the secant values of elastic modulus and Poisson coefficient, which are properly updated during the analysis. As confirmed by comparisons with experimental data, the followed procedure is able to represent the dilatation and crushing of concrete under compressive loads and, due to its versatile nature, it can be easily extended to fiber reinforced elements.
•FE analysis of cracked RC ties through 1D, 2D, 3D discrete models.•Comparison between experimental and numerical response of RC ties.•Investigation of multiaxial stress diffusion in the concrete ...blocks between cracks.•Improvement of numerical results through inclusion of damage in the bond–slip law.•Improvement of numerical results through inclusion of secondary cracks.
This paper aims to investigate the role and effect of stress diffusion and bond deterioration in the analysis of reinforced concrete ties. Although tension ties seem to be basically in a uniaxial state of stress, after the onset of cracking the problem presents a multiaxial diffusion of stresses. In this paper, a uniaxial 1D numerical model has been compared with more sophisticated 2D and 3D Finite Element (FE) models, in order to investigate the different level of accuracy and information that can be attained considering or not the multiaxial state of stress. The obtained results show that the contribution of stress diffusion in concrete blocks between cracks has a certain importance for the evaluation of the global and local behavior of investigated tension ties, but it does not alter completely the response. Furthermore, the inclusion of damage in the bond–slip law due to the presence of “cone” cracks improves the description of the element behavior especially in the stabilized cracking stage. The same applies if thin secondary cracks are taken into account.
► Modeling of steel fiber reinforced concrete (SFRC) post-cracking behavior. ► Adoption of a properly developed constitutive model to perform NLFE analyses. ► Modeling of fiber contributions: tension ...softening and tension stiffening. ► Model validation: comparison between experimental and numerical results.
This paper aims to investigate and model the post-cracking behavior of steel fibre reinforced concrete (SFRC) elements, which is characterized by more distributed, narrower and closely spaced cracks with respect to ordinary reinforced concrete. A numerical procedure based on non-linear fracture mechanics concepts has been developed to take into account the main mechanisms governing the problem, namely the tension softening, related to the bridging effect provided by aggregates and fibers across cracks, and the tension stiffening between steel bars and surrounding concrete. The effectiveness of the proposed approach has been then verified through comparisons with significant experimental tests available in technical literature concerning SFRC slabs, tension ties and beams.
The behavior of cracked reinforced concrete structural components is here analyzed through a three-dimensional model, which includes all the interface phenomena generated along cracks, such as ...aggregate bridging and interlock, tension stiffening and dowel action, as well as the non-linear response of concrete in compression and in tension. The model is able to effectively describe the progressive development of multi-axial cracking, by considering the crack re-orientation and the change of the crack spacing as loading increases. The proposed formulation, which is expressed in terms of secant stiffness matrix, is obtained by taking into account the flexibility contributions of cracks and of the concrete between adjacent cracks, in both the singly and the multi-cracked stage. Finally, this model is implemented into a finite element code and is validated through comparisons with significant experimental data available in the literature.
Shrinkage effects on short-term behavior of reinforced concrete elements are often neglected both in design code provisions and in numerical simulations. However, it is known that their influence on ...serviceability performance can be significant, especially in case of lightly-reinforced beams. As a matter of fact, the restraint provided by the reinforcement on concrete determines a reduction of the cracking load of the structural element, as well as an increase of its deflection. This paper deals with the modeling of early-age shrinkage effects in the field of smeared crack approaches. To this aim, an existing non-linear constitutive relation for cracked reinforced concrete elements is extended herein to include early-age concrete shrinkage. Careful verifications of the model are carried out by comparing numerical results with significant experimental data reported in technical literature, providing a good agreement both in terms of global and local behavior.
In this work, a consistent formulation for the representation of concrete behavior before and after cracking has been implemented into a non-linear model for the analysis of reinforced concrete ...structures, named 2D-PARC. Several researches have indeed pointed out that the adoption of an effective modeling for concrete, combined with an accurate failure criterion, is crucial for the correct prediction of the structural behavior, not only in terms of failure load, but also with reference to a realistic representation of crack initiation and development. This last aspect is particularly relevant at serviceability conditions in order to verify the fulfillment of structural requirements provided by Design Codes, which limit the maximum crack width due to appearance and durability issues. In more details, a constitutive model originally proposed by Ottosen and based on non-linear elasticity has been here incorporated into 2D-PARC in order to improve the numerical efficiency of the adopted algorithm, providing at the same time an accurate prediction of the structural response. The effectiveness of this procedure has been verified against significant experimental results available in the technical literature and relative to reinforced concrete beams without stirrups failing in shear, which represent a problem of great theoretical and practical importance in the field of structural engineering. Numerical results have been compared to experimental evidences not only in terms of global structural response (i.e. applied load vs. midspan deflection), but also in terms of crack pattern evolution and maximum crack widths.
A macro-scale approach to R/C modeling is proposed in this paper by formulating a comprehensive model, that describes R/C behavior in the uncracked stage (solid concrete) and in the cracked stage, ...the latter with either unidirectional cracking (primary cracks) or with bidirectional cracking (primary and secondary cracks) or even multi-directional cracking. The secant stiffness matrix is formulated by means of a direct procedure, based on the assumption that the solid concrete and the reinforcement work in parallel, while the solid concrete between the cracks and the cracks themselves work in series. The resistant mechanisms active at the crack interface are introduced by means of their highly nonlinear laws, that are taken from the literature and are based on well-documented tests. The reliability and accuracy of the proposed model are checked against a few well-documented tests on 2D R/C members failing past the formation of secondary cracks.
A method is proposed for the analysis of the nonlinear behavior up to failure of reinforced-concrete membrane elements. The approach considers a linear elastic behavior for concrete before cracking; ...after cracking, the cracks are assumed as having a fixed direction and uniform spacing and cracked reinforced concrete is modeled as an orthotropic material. The basic element of cracked reinforced-concrete membrane is defined and the related stiffness matrix is proposed. The quantities that govern the problem are the opening and the sliding of the crack lips, as well as the strain of the concrete struts that are located between cracks. Applied to a local analysis of cracked reinforced concrete, the above variables allow for the effective modeling of compatibility and equilibrium conditions and take into account phenomena such as aggregate interlock, tension stiffening, and dowel action. To verify the reliability and capability of the proposed method, some comparisons with experimental observations of relevant tests are made.
This work discusses and compares different numerical approaches that can be adopted for the analysis up to failure of reinforced concrete beams, also when they experience a brittle shear collapse. ...Since the development of inclined shear cracks causes a variation of the strain field normal to the element axis, as well as of the shear strains in the beam depth, this type of problem is often dealt with refined bi-dimensional nonlinear finite element analyses. The effectiveness of this type of simulations is in turn mainly related to the adoption of a sound constitutive law for the material. This work highlights that, given the same material model, also more “traditional” approaches, based on sectional analysis or on 1D finite element simulations, can be satisfactorily applied to study the problem, if their kinematic assumptions are improved and extended. In these cases, a subdivision of beam depth into several layers is also recommended. In fact, this allows to both simulate the actual position of steel reinforcement, and to widen the applicability of the method to elements characterized by a generic cross-section shape.
•Two simplified methods are proposed to analyze shear critical RC beams.•The methods are respectively based on sectional analysis and 1D FE analysis.•The results are compared with standard 2D NLFEA and experimental test results.•The results show that both the methods simulate the failure behavior properly.•The 1D FE model can be also used to predict beam structural behavior in D-regions.
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