Mechanical damage in concrete and other cohesive materials
- Autores: José Joaquín Ortega Parreño
- Directores de la Tesis: Gonzalo Ruiz López (dir. tes.), X.X. Zhang (codir. tes.)
- Lectura: En la Universidad de Castilla-La Mancha ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Chengxiang Yu (presid.), Héctor Cifuentes Bulté (secret.), Vitor Manuel Couto Fernandes Cunha (voc.)
- Programa de doctorado: Programa de Doctorado en Territorio, Infraestructuras y Medio Ambiente por la Universidad de Castilla-La Mancha
- Materias:
- Enlaces
- Tesis en acceso abierto en: RUIdeRA
- Resumen
Concrete is one of the main and most extended construction materials. Therefore, the control of the damage in concrete is fundamental for the maintenance of current structures and the design of new ones. The failure or fracture behaviour of this type of quasi-brittle materials is studied through diverse methods like direct testing or statistical, analytical or numerical models. In this thesis, various of these approaches have been applied to the analysis of different types of damage in concrete and other cohesive materials like lime mortars. In this manner, contributions to the research in relevant fields of this topic have been made.
The first area treated in the thesis is the fatigue of concrete. In particular, the error committed in its probabilistic characterisation has been studied. The scatter of fatigue life results for a given stress level can be very high, even of several orders of magnitude. This behaviour can be described by means of a probabilistic distribution, which is obtained by fitting experimental results. However, due to the large variability of cycles to failure that concrete presents, the number of tests becomes a highly influential factor in the quality of the estimated distribution, which is usually disregarded. Based on a set of 100 experimental values, a statistical method has been developed to estimate the maximum possible error in the distribution definition for a given probability and safety margin. With the results provided by the method, the number of tests can be optimised and a design fatigue distribution can be defined for the corresponding concrete.
Next, the analytical double-K method is revised. The method characterises concrete fracture in mode I through two toughness parameters by applying an elastic equivalence. The method is applied to a set of results from different specimen sizes and loading rates. The parameter K(Ic)(un), corresponding to the maximum load, increases with both the specimen size and the loading rate. Regarding K(Ic)(ini), corresponding to the crack initiation, the method obtains it by an analytical procedure which fails for large specimen sizes. Two proposals are made to obtain K(Ic)(ini) in a different way. The first one is to obtain the parameter through the corresponding crack initiation load directly measured on the load-crack mouth opening curve. The second proposal applies some improvements in the evaluation of the cohesive stresses, which corrects the previous procedure. Finally, the influence of the loading rate is introduced in the method by a viscous factor applied to the cohesive law.
The last part of the thesis presents the application of numerical methods to the study of fracture. First, a type of metal anchors for concrete that are not covered by standards is studied. The performance of four different geometrical configurations is analysed for tension and shear loads. The results of a numerical model for each case are compared and validated with previous experimental results. These models allow further analyses to study the effect of different variables. As general conclusions, the anchor capacity improves for better mechanical anchorage and concrete confinement and strength.
Finally, the size effect on the compressive strength of lime mortars is studied by a numerical analysis. The standard test measures this strength with prisms of 40 mm in depth. In a previous experimental programme, the strength provided by cylinders of 150 mm in height was also obtained for two different mortars, which was smaller. A model of the standard test with prisms was validated with the experimental results and, later, tests with two larger specimen sizes of 80 mm and 160 mm in depth were simulated. With the results, the size effect law is obtained for each mortar. The conclusion is that the strength given by cylinders is very similar to the real material strength while the standard prisms offer values around a 50 or 60% higher.
