Gianluca Mazzucco

An approach for modelling concrete spalling in finite strains

A new approach for modelling concrete spalling process is here proposed, taking into account a fully nonlinear-displacement/strain theory able to catch complex interactions between pressure, thermal and mechanical fields. The micro-structural modelling of concrete under fire conditions is derived from a mechanical and thermodynamic consistent theory and it is strictly related to a self-consistent, carefully extracted set of experimental data, in order to make a correct validation and calibration of the numerical F.E. procedures and codes. Even if appearing as a first but successful example, it is shown that a procedure accounting for coupled material and geometric nonlinearities is able to attain valuable and realistic numerical results concerning spalling process in concrete.

Three‐dimensional modelling of bond behaviour between concrete and FRP reinforcement

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 Mazarss 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 conta...

Mechanical and durability behaviour of growing concrete structures

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 condition...

Large Membrane Roof Analysis: Nonlinear Modeling of Structures, Connectors, and Experimental Evidences

This work discusses the numerical and physical models developed for the design of a membrane roof for the Baptist Church of Fortaleza as well as the fabrication and construction of the actual membrane, comparing results of the models with those of the real structure. The roof area amounts to about 2,900  m2 , a national record for flexible border membranes and, to the writers’ knowledge, the first case of a fully computer-assisted design process within Brazil. The paper initially outlines procedures to form finding, stress analysis, and patterning, and then focuses on the physical models developed to validate them. Finally, construction of the actual membrane is described, and comparison is made with the previous numerical and physical models. Determination of the mechanical properties of the fabrics used to construct the membrane is also briefly discussed. Additionally, analyses of the geometric configuration and definition of the structural response of typical connectors of such a tension structure, col...

Numerical simulation and experimental validation of a coupled mechanical-thermal-electrical contact model

A three-dimensional mechanical-electrical-thermal coupled model is presented and validated both numerically and experimentally on a classical sphere-plane contact problem. The proposed approach combines a innovative Cell Method (CM) approach for the thermal-electrical analysis with a conventional FEM code for the mechanical analysis. Surface roughness and contact spot density are modeled by means of statistical parameters that can be easily included in a CM model. These parameters depend on the apparent contact pressure whose distribution is assessed with FEM. Numerical and experimental results are discussed in the paper.

Modelling a Coupled Thermoelectromechanical Behaviour of Contact Elements via Fractal Surfaces

A three-dimensional coupled thermoelectromechanical model for electrical connectors is here proposed to evaluate local stress and temperature distributions around the contact area of electric connectors under different applied loads. A micromechanical numerical model has been developed by merging together the contact theory approach, which makes use of the so-called roughness parameters obtained from experimental measurements on real contact surfaces, with the topology description of the rough surface via the theory of fractal geometry. Particularly, the variation of asperities has been evaluated via the Weierstrass-Mandelbrot function. In this way the micromechanical model allowed for an upgraded contact algorithm in terms of effective contact area and thermal and electrical contact conductivities. Such an algorithm is subsequently implemented to construct a global model for performing transient thermoelectromechanical analyses without the need of simulating roughness asperities of contact surfaces, so reducing the computational cost. A comparison between numerical and analytical results shows that the adopted procedure is suitable to simulate the transient thermoelectromechanical response of electric connectors.

Fire Spalling Prevention via Polypropylene Fibres

A deep understanding of concrete at the mesoscale level is essential for a better comprehension of several concrete phenomena, such as creep, damage, and spalling. The latter one specifically corresponds to the separation of pieces of concrete from the surface of a structural element when it is exposed to high and rapidly rising temperatures; for this phenomenon a mesoscopic approach is fundamental since aggregates performance and their thermal properties play a crucial role. To reduce the risk of spalling of a concrete material under fire condition, the inclusion of a low dosage of polypropylene fibres in the mix design of concrete is largely recognized. PP fibres in fact evaporate above certain temperatures, thus increasing the porosity and reducing the internal pressure in the material by an increase of the voids connectivity in the cement paste. In this work, the contribution of polypropylene fibres on concrete behaviour, if subjected to elevated thermal ranges, has been numerically investigated thanks to a coupled hygrothermomechanical finite element formulation. Numerical analyses at the macro- and mesoscale levels have been performed.