Numerical Simulation of the Interaction between Fibre Concrete Slab and Subsoil—The Impact of Selected Determining Factors
Abstract
:1. Introduction
- the increased load-bearing capacity of concrete structure
- reduction of concrete slab thickness
- increased durability
- low maintenance costs
- improved flexural properties
- reduced site work for managing steel reinforcement
- reduced project costs
- increased impact and abrasion resistance
2. Materials & Methods
2.1. Fundamental Characteristics and Results of Experimental Fibre Concrete Slab Testing
2.2. Numerical Modelling of the Fibre Slab-Subsoil Interaction
3. Results
- evaluation of the dependence of the vertical displacements of the slab on the applied constitutive model of the slab material (assuming identical input characteristics of Mohr-Coulomb and Drucker-Prager model), comparison of results
- assessment of vertical displacements and deflection of slab corresponding to the variant shear strength parameters of subsoil assuming Mohr-Coulomb model of both slab and subsoil (without interface elements), comparison with monitored results
- assessment of vertical displacements and deflection of slab corresponding to the variant Young’s modulus of subsoil assuming Mohr-Coulomb model of both slab and subsoil (without interface elements), comparison with monitored results
- evaluation of interface elements effect on the vertical displacements and deflection of the slab assuming Mohr-Coulomb model of both slab and subsoil, comparison with monitored results
3.1. Evaluation of the Dependence of the Vertical Displacements of the Slab on the Applied Constitutive Model of the Slab Material
3.2. Assessment of Vertical Displacements and Deflection of Slab Corresponding to the Variant Shear Strength Parameters of Subsoil Assuming Mohr-Coulomb Model of Both Slab and Subsoil (without Interface Elements), Comparison with Monitored Results
3.3. Assessment of Vertical Displacements and Deflection of Slab Corresponding to the Variant Young’s Modulus of Subsoil Assuming Mohr-Coulomb Model of Both Slab and Subsoil (without Interface Elements), Comparison with Monitored Results
3.4. Evaluation of Interface Elements Effect on the Vertical Displacements of the Slab
4. Conclusions
- From the quantitative point of view the Mohr-Coulomb model of slab overestimated both the results of vertical displacements of slab based on the elastic or Drucker-Prager model and experimental results (the difference between the max. vertical displacements assuming Mohr-Coulomb model and experimental measurements achieved 12% in this study). Thus, Mohr-Coulomb model of slab (assuming Mohr-Coulomb model of subsoil) assessed the maximal vertical displacements of the centre of slab on the safety side. The measured maximum vertical displacement in the centre of the slab (under the compressive stressed part of slab) was not achieved with the elastic, Mohr-Coulomb and the Drucker-Prager constitutive models. Mohr-Coulomb overestimated the maximum vertical displacements in the slab centre, while Drucker-Prager underestimated this maximum value for the same input data. In the tensile stressed part of slab both elastoplastic constitutive models overestimated the measured value of vertical displacements. Elastic model underestimated the experimental results (about 37%).
- From the qualitative point of view (shape of deflection curve), the numerical simulation showed the better agreement of the Mohr-Coulomb constitutive model with the experimental measurements in comparison with both other constitutive models. Unlike the elastic and Drucker-Prager model, the curves of both measured and calculated vertical displacements using Mohr-Coulomb model were characterized by the significant differences between the centre of slab and its edge, which corresponds better with the observed real behaviour of slab. But even with the application of Mohr-Coulomb model, experimentally investigated greater deflection was not achieved. Thus, none of the considered constitutive models was able to capture the real shape of the deflection curve in this study, the model indicated smaller deflections of the slab.
- The results, assuming elastic constitutive model, confirmed the unsuitability of the application of this simple elastic constitutive model to the modelling of slab-subsoil interaction from both qualitative and quantitative point of views.
- Assuming Mohr-Coulomb constitutive model of slab without the interface, the shear strength characteristics of subsoil (cohesion and friction angle) affected the maximum vertical displacements in the centre of slab, but there is no effect on the vertical displacements at the edges after the lift of a boundary parts of slab was manifested. With the reduction of the shear strength characteristics of the subsoil, a larger deflection of the slab was achieved in the model, but nevertheless the experimentally measured deflection curve (reflected in internal forces inside of slab) was achieved by the numerical model based on the Mohr-Coulomb constitutive model.
- The Mohr-Coulomb model of slab without interface showed that the calculated vertical displacement of the edges of slab remained the same regardless of the slab load after the lift of a boundary part of the slab was manifested. Of course, the maximum vertical displacements in the centre of slab increased with increasing load.
- The change of deformation characteristics in the subsoil did not lead to the achievement of the measured deflection of the slab after the lift of a boundary part of slab was manifested. Only the maximum vertical measured displacement in the centre of slab was achieved by the model changing the subsoil strength and deformational characteristics.
- The need to apply contact (interface) elements has been shown in this study. These elements can to take into account the reduction of the contact area between the slab and the subsoil resulted from the experimentally observed significant deflection and gapping occurrence between the slab and the subsoil. The effect of interface elements was not significant in case of lower load without manifestation of significant plastic deformation. But for the higher load, the application of contact elements in the model led to a more realistic view of the slab-subsoil interaction, to the redistribution of contact stress in the subsoil from the central part towards the edges and to the lift of the corners of the slab.
- Numerical model based on the finite element method (using MIDAS GTS NX software), assuming Mohr-Coulomb constitutive model for both of slab and subsoil material, can be used to the modelling of slab- subsoil interaction, but certain above mentioned limitations of the modelling results should be taken into account. Especially, assuming elastic, Mohr-Coulomb or Drucker-Prager constitutive model, modelled deflection and the resulting internal forces inside the slab could be underestimated.
- To obtain more reliable results from of the both qualitative and quantitative points of view, it would be necessary to apply more advanced constitutive models of both subsoil and fibre concrete slabs, considering the hardening and softening phenomenon of material and the partial loss of stiffness due to the cracking of concrete [44]. Attention must be also paid to further study of the properties and the behaviour of interface elements and to other numerical methods, including mesh free methods of cracks mechanics [45,46].
- The performed study confirmed that the problem of slab-subsoil interaction is associated significantly with both the geotechnical and structural engineering. Every user of specialized software, whether geotechnical or structural, should be aware of the fact that certain aspects of the previously mentioned engineering areas are emphasized at the expense of others in this software. In specialized geotechnical software (MIDAS GTS NX, PLAXIS, etc.) the structural elements are usually more simplified (often only their elastic behaviour is considered), but the subsoil can be modelled in the more details. On the other hand, the specialized structural software (ANSYS, SCIA Engineer etc.) have option to detailed modelling of structural element behaviour, but the subsoil behaviour is usually more simplified. This fact is necessary to consider when assessing the reliability of the results of numerical models. It is optimal to verify the results of modelling by monitoring, as was done in this presented contact problem.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Slab No. | Concrete | Dosage of Fibers kg/m3 | Compressive Strength [MPa] (Cylindrical Samples—An Average of 3 Tests) | Compressive Strength [MPa] (Cubic Samples—An Average of 6 Tests) | Young’s Module of Elasticity [GPa] (Cylindrical Samples—An Average of 3 Tests) |
---|---|---|---|---|---|
G05 | C 20/25 | 25 | 24.86 | 30.9 | 19.7 |
Unit Weight kN/m3 | Elastic Modulus MPa | Poisson’s Ration | Cohesion kPa | Friction Angle deg- | |
---|---|---|---|---|---|
Subsoil | 19 | 12 | 0.35 | 9 | 19 |
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Duris, L.; Hrubesova, E. Numerical Simulation of the Interaction between Fibre Concrete Slab and Subsoil—The Impact of Selected Determining Factors. Sustainability 2020, 12, 10036. https://doi.org/10.3390/su122310036
Duris L, Hrubesova E. Numerical Simulation of the Interaction between Fibre Concrete Slab and Subsoil—The Impact of Selected Determining Factors. Sustainability. 2020; 12(23):10036. https://doi.org/10.3390/su122310036
Chicago/Turabian StyleDuris, Lukas, and Eva Hrubesova. 2020. "Numerical Simulation of the Interaction between Fibre Concrete Slab and Subsoil—The Impact of Selected Determining Factors" Sustainability 12, no. 23: 10036. https://doi.org/10.3390/su122310036