Resumen de Metodología y validación experimental para el estudio de la influencia de los rellenos en el comportamiento sísmico de pórticos
José Barros Cabezas
Nowadays, one of the most widely used structural building systems consists of masonry infilled frames, in which the walls are intended to protect the interior of the building from environmental conditions. The construction of these walls is well known by practitioners and has been attractive for its low cost and its ability to isolate different environments of a building. In most cases, the aforementioned walls are considered as non-structural elements; however, the observation made on the behaviour of this type of structures, especially after the occurrence of seismic events, has shown that these elements effectively collaborate with the rest of the structure in withstanding the event.
The structural system of masonry infilled frames has a large number of variables that condition its behaviour. Among the most influential variables we can mention: (1) the masonry units: the variety of materials used, the different forms of manufacture, quality and geometry, (2) the bonding mortar between masonry units: the different materials and dosages used and the bonding quality achieved between the masonry units, (3) the bonding quality between the wall and the portal frame: the existence of stress transfer elements or the direct interaction of the mortar with the frame material, (4) the construction process and the expertise of the workmanship, (5) the interaction between the behaviour of the wall in and out of its plane, (6) the existence of openings (doors and/or windows) in the wall. The aforementioned variables constitute sources of uncertainty that denote the difficulty of characterizing the seismic-resistant behaviour of this system, been particularly important when deterministic methodologies are going to be used.
The main objective of this thesis is to provide tools to evaluate existing masonry infilled frame structures. In this sense, the use of probabilistic tools has been explored to propose techniques to predict the behaviour of buildings with this structural system. First, the use of approximate Bayesian computational algorithms is studied to infer non-linear numerical modelling parameters of masonry infilled frames, taking as a reference the results of laboratory testing. An improvement to the original ABC-SubSim algorithm is proposed, for ease of use by autonomously estimating a series of meta-parameters that influence the speed of calculation and quality of the result. This new algorithm has been named A2BC-SubSim, which has been proven to achieve a balance between computational speed and result quality, after the solution of some numerical examples. On the other hand, the application of neural networks to predict the constitutive behaviour of the structural system was also explored. A database of existing tests was developed in order to train such networks; however, due to the limited number of tests available in the literature, it was chosen to work with Bayesian neural networks, which have the advantage of also providing information on the quality of the prediction made. The prediction capabilities of the trained network is checked against measurements of laboratory tests that were not part of the training group, achieving promising results.
Finally, laboratory tests were performed to study the relationship between the out-of-plane fundamental frequency of the wall versus the stiffness of the system in the plane of the wall. With the results of these tests and a parametric study using complex numerical models, a semi-empirical and non-destructive methodology has been proposed to estimate the stiffness of existing masonry infilled frames. The methodology was checked with measurements of specimens tested on a seismic table, demonstrating the feasibility of application of the proposed methodology.
