Gianluca Mazzucco, Beatrice Pomaro, Giovanna Xotta, Carmelo E. Maiorana and Valentina A. Salomoni
The purpose of this paper is the numerical assessment of concrete behaviour close to failure, via the development of robust elastoplastic models inclusive of damage effects. If…
Abstract
Purpose
The purpose of this paper is the numerical assessment of concrete behaviour close to failure, via the development of robust elastoplastic models inclusive of damage effects. If mesoscale investigations are to be considered, the model must take into account the local confinement effects because of the presence of aggregate inclusions in the cement paste and, correspondingly, the possibility to account for local 3D stress states even under uniaxial compression. Additionally, to enhance the predictive capabilities of a mesoscale representation, the reconstructed geometry must accurately follow the real one.
Design/methodology/approach
The work provides a procedure that combines a 3D digital image technique with finite element (FE) modelling thus maintaining the original 3D morphology of the composite.
Findings
The potentialities of the proposed approach are discussed, giving new insights to a FE modelling (FEM)-based approach applied together with a computer-aided design. Coupled mechanisms of mechanical mismatch and confinement, characterizing the combined cement matrix-aggregates effect, are captured and highlighted via the numerical tests.
Originality/value
The novelty of this research work lies in the proposal of a digitally based methodology for a precise concrete reconstruction together with the adoption of an upgraded elastic–plastic damage model for the cement paste.
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Giovanna Xotta, Valentina A. Salomoni and Carmelo E. Majorana
Knowledge of the behavior of concrete at mesoscale level requires, as a fundamental aspect, to characterize aggregates and specifically, their thermal properties if fire hazards…
Abstract
Purpose
Knowledge of the behavior of concrete at mesoscale level requires, as a fundamental aspect, to characterize aggregates and specifically, their thermal properties if fire hazards (e.g. spalling) are accounted for. The assessment of aggregates performance (and, correspondingly, concrete materials made of aggregates, cement paste and ITZ – interfacial transition zone) is crucial for defining a realistic structural response as well as damage scenarios.
Design/methodology/approach
It is here assumed that concrete creep is associated to cement paste only and that creep obeys to the B3 model proposed by Bažant and Baweja since it shows good compatibility with experimental results and it is properly justified theoretically.
Findings
First, the three‐dimensionality of the geometric description of concrete at the meso‐level can be appreciated; then, creep of cement paste and ITZ allows to incorporate in the model the complex reality of creep, which is not only a matter of fluid flow and pressure dissipation but also the result of chemical‐physical reactions; again, the description of concrete as a composite material, in connection with porous media analysis, allows for understanding the hygro‐thermal and mechanical response of concrete, e.g. hygral barriers due to the presence of aggregates can be seen only at this modelling level. Finally, from the mechanical viewpoint, the remarkable damage peak effect arising from the inclusion of ITZ, if compared with the less pronounced peak when ITZ is disregarded from the analysis, is reported.
Originality/value
The fully coupled 3D F.E. code NEWCON3D has been adopted to perform fully coupled thermo‐hygro‐mechanical meso‐scale analyses of concrete characterized by aggregates of various types and various thermal properties. The 3D approach allows for differentiating each constituent (cement paste, aggregate and ITZ), even from the point of view of their rheologic behaviour. Additionally, model B3 has been upgraded by the calculation of the effective humidity state when evaluating drying creep, instead than using approximate expressions. Damage maps allows for defining an appropriate concrete mixture to withstand spalling and to characterize the coupled behaviour of ITZ as well.
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Valentina A. Salomoni, Carmelo E. Majorana, Giuseppe M. Giannuzzi and Adio Miliozzi
The purpose of this paper is to describe an experience of R&D in the field of new technologies for solar energy exploitation within the Italian context. Concentrated solar power…
Abstract
Purpose
The purpose of this paper is to describe an experience of R&D in the field of new technologies for solar energy exploitation within the Italian context. Concentrated solar power systems operating in the field of medium temperatures are the main research objectives, directed towards the development of a new and low‐cost technology to concentrate the direct radiation and efficiently convert solar energy into high‐temperature heat.
Design/methodology/approach
A multi‐tank sensible‐heat storage system is proposed for storing thermal energy, with a two‐tanks molten salt system. In the present paper, the typology of a below‐grade cone shape storage is taken up, in combination with nitrate molten salts at 565°C maximum temperature, using an innovative high‐performance concrete for structures absolving functions of containment and foundation.
Findings
Concrete durability in terms of prolonged thermal loads is assessed. The interaction between the hot tank and the surrounding environment (ground) is considered. The developed FE model simulates the whole domain, and a fixed heat source of 100°C is assigned to the internal concrete surface. The development of the thermal and hygral fronts within the tank thickness are analysed and results discussed for long‐term scenarios.
Originality/value
Within the medium temperature field, an innovative approach is here presented for the conceptual design of liquid salts concrete storage systems. The adopted numerical model accounts for the strong coupling among moisture and heat transfer and the mechanical field. The basic mathematical model is a single fluid phase non‐linear diffusion one based on the theory by Bažant; appropriate thermodynamic and constitutive relationships are supplemented to enhance the approach and catch the effects of different fluid phases (liquid plus gas).
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Valentina A. Salomoni, Gianluca Mazzucco and Carmelo E. Majorana
This paper seeks to analyse 3D growing concrete structures taking into account the phenomenon of body accretion, necessary for the simulation of the construction sequence, and…
Abstract
Purpose
This paper seeks to analyse 3D growing concrete structures taking into account the phenomenon of body accretion, necessary for the simulation of the construction sequence, and carbon dioxide attack.
Design/methodology/approach
A typical 3D segmental bridge made of precast concrete is studied through a fully coupled thermo‐hygro‐mechanical F.E. model. The durability of the bridge is evaluated and carbonation effects are considered. Creep, relaxation and shrinkage effects are included according to the theory developed in the 1970s by Bažant for concretes and geomaterials; the fluid phases are considered as a unique mixture which interacts with a solid phase. The porous material is modelled using n Maxwell elements in parallel (Maxwell‐chain model).
Findings
First, calibration analyses are developed to check the VISCO3D model capabilities for predicting carbonation phenomena within concrete and the full 3D structure is modelled to further assess the durability of the bridge under severe conditions of CO2 attack.
Originality/value
The adopted numerical model accounts for the strong coupling mechanisms of CO2 diffusion in the gas phase, moisture and heat transfer, CaCO3 formation and the availability of Ca(OH)2 in the pore solution due to its transport by water movement. Additionally, the phenomenon of a sequential construction is studied and numerically reproduced by a sequence of “births” for the 3D finite elements discretizing the bridge. The fully coupled model is here extended to 3D problems for accreting bodies (as segmental bridges) in order to gather the effects of multi‐dimensional attacks of carbon dioxide for such structures.
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Nicolò Spiezia and Valentina Anna Lia Salomoni
This paper proposes a unified original general framework, designed to theoretically develop and to extremely easily implement elastoplastic constitutive laws defined in the so…
Abstract
Purpose
This paper proposes a unified original general framework, designed to theoretically develop and to extremely easily implement elastoplastic constitutive laws defined in the so called two-invariants space, both in small and finite strain regime.
Design/methodology/approach
A general return mapping algorithm is proposed, and particularly a standard procedure is developed to compute the two algorithmic tangent operators, required to solve the Newton–Raphson scheme at the local and global level and thus cast the elastoplastic algorithm within a FEM code.
Findings
This work demonstrates that the proposed procedure is fully general and can be applied whatever is the elastic law, the yield surface, the plastic potential function and the hardening law. Several numerical examples are reported, not only to demonstrate the accuracy and robustness of the algorithm, but also explain how to use this general algorithm also in other applications.
Originality/value
The proposed algorithm and its numerical implementation into a FEM code is new and original. The usefulness and the value of the algorithm is twofold: (1) it can be implemented in a small and finite strain simulation FEM code, in order to handle different types of constitutive laws in the same modular way, thus fully leveraging on modern object-oriented coding approach; (2) it can be used as a framework to develop (and then to implement) new constitutive models, since the researcher can simply define the relevant functions (and its main derivatives) and automatically get the numerical algorithm.
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Valentina Salomoni, Gianluca Mazzucco, Carlo Pellegrino and Carmelo Majorana
The purpose of this paper is to investigate the bond behaviour between fiber reinforced polymer (FRP) sheets and concrete elements, starting from available experimental evidences…
Abstract
Purpose
The purpose of this paper is to investigate the bond behaviour between fiber reinforced polymer (FRP) sheets and concrete elements, starting from available experimental evidences, through a calibrated and upgraded 3D mathematical‐numerical model.
Design/methodology/approach
The complex mechanism of debonding/peeling failure of FRP reinforcement is studied within the context of damage mechanics to appropriately catch transversal effects and developing a more realistic and comprehensive study of the delamination process. The FE ABAQUS© code has been supplemented with a numerical procedure accounting for Mazars's damage law inside the contact algorithm.
Findings
It has been shown that such an approach is able to catch the delamination evolution during loading processes as well.
Originality/value
A Drucker‐Prager constitutive law is adopted for concrete whereas FRP elements are assumed to behave in a linear‐elastic manner, possibly undertaking large strains/displacements. Surface‐to‐surface contact conditions have been applied between FRP and adjacent concrete, including the enhancement given by the strain‐softening law according to Mazars' damage model. The procedure has been introduced to describe the coupled behaviour between concrete, FRP and adhesive resulting in specific bonding‐debonding features under different load levels.