Análisis numérico termo-mecánico y termo-higrométrico del hormigón expuesto a altas temperaturas
- Autores: Mariana Rodriguez Frete
- Directores de la Tesis: Ignacio Carol Vilarasu (dir. tes.), Carlos María López Garello (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2020
- Idioma: español
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
Concrete is one of the most used materials in construction, and its application spans to all kinds of structures. For this reason, concrete has been the subject of intense study. In spite of that, there are still apects of its behavior that are not completely unerstood and require further research, such as those related to material durability, i.e. aspects related to the deterioration due to environmental actions such as for instance high temperatures, chemical or biological attack, etc.
The present doctoral thesis focuses on the numerical study of concrete behavior subject to high temeperatures. Nowadays it seems clear that two main mechanisms exist that may lead to material failure or spalling (sudden explosive detachment or outer concrete layers) when concrete is exposed to high temperatures (fire). The first one is related to the develoment of high compresive stresses as the result of restricted termal dilation, and the second one is related to the development of vapor pressures within the material pores due to water vaporization. Both mechanisms are studied independently in this Thesis.
In this context of the high temeprature effects in concrete, most numerical studies in the literature are based on a macroscopic approach, in which the material is considered a homogeneous continuum. However, it is clear that concrete is a heterogeneous material and that its overall behavior strongly depends on the response of each one of its constituents and the interaction between them. In this regard, the approach to the first of the two above-mentioned mechanisms, is carried out using two independent Finite Element codes in-house developed within the MECMAT-UPC research group: the duffusion code DRACFLOW and the meso-mechanical code DRAC. In both analyses, the material is considered as heterogeneous, composed of aggregates and mortar, each of them with different thermal and mechanical properties. The results of various uncoupled calculations under uniform and non-uniform temperature distrubutions, are compared to experimental results from the literature. Numerical results of a thermo-mechanical análisis are also presented. These results represent spalling more realistically, in better agreement with the behavior observed in coulmns exposer to the fire action.
On the other hand, a main contribution of this thesis is the formulation and implementaiotn of a hygro-mechanical TH model (second failure mechanism mentioned above). In this TH formulation, temperature and water vapor pressure are conssidered the primary variables, from which the rest of the field and state variables may be obtained. A novel formulation is also proposed to relate saturation degree and vapor pressure, which is based on the combination of the pore distribution curve with some fundamental equations of termodinamical equilibrium between water vapor and liquid water in the pores. Various 1-D examples of applcation are selected for the validation of the model. The results obtained succeed in reproducing satisfactorily a variety of complex aspects of the phenomenon. Finally, results are presented of the application of the model to the TH analysis of a meso-structural concrete sample
