1. Doctorado

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Prediction of failure of sands under constant volume general cyclic simple shear loading using specific dissipated energy
(Pontificia Universidad Católica del Perú, 2023-01-30) Zavala Rosell, Guillermo José; Aguilar Vélez, Rafael; Pando López, Miguel Ángel
Seismic soil liquefaction is a recurring phenomenon that may cause significant damage to infrastructure during earthquakes and that in turn may also cause injuries and even fatalities. This phenomenon has been widely studied by researchers, and for its study the laboratory characterization of behavior of sands when subjected to cyclic loading is very important. One of the approaches for this kind of studies is through the calculation of the energy that is dissipated by the soil when it is subjected to cyclic loading. One of the hypotheses for utilizing these energy methods states that the cumulative dissipated energy required in a soil to reach failure only depends on the initial state of the sample (relative density and initial vertical effective stress) and should be reasonably constant and independent of the loading amplitude and waveform applied to the sample. This thesis work seeks to evaluate the validity of this hypothesis. Also, based on this hypothesis, it seeks to develop a simplified methodology to predict failure of sands when subjected to general cyclic loading, performing only simple harmonic tests. The hypothesis for the development of this methodology is that there is a relationship between the initial state of the sample and the cumulative dissipated energy to failure in cyclic simple shear test. To reach these goals, over 250 uniform and non-uniform constant volume cyclic simple shear tests were performed on Ottawa 20/30 sand, and the dissipated energy to failure was measured in each of these tests. The experimental program showed that the measured cumulative dissipated energy to failure was reasonably constant for the same initial sample conditions, but with some variability inherent to geotechnical laboratory testing. As expected, the cumulative dissipated energy increased with increasing initial stress level and relative density. Also, a simplified method to predict the dissipated energy to failure of a sample subjected to general cyclic loading, based on a multivariable regression performed on a simplified set of laboratory results, is presented, and it is next validated with two independent data sets. In both cases the method was found to yield reasonable predictions of failure of sands when subjected to complex and irregular cyclic shear loading.
Assessment of the influence of environmental conditions in historical adobe buildings through long-term structural monitoring
(Pontificia Universidad Católica del Perú, 2019-02-11) Zonno, Giacomo; Aguilar Vélez, Rafael; Boroschek Krauskopf, Rubén Luis; Lourenço, Paulo José Brandão Barbosa
Historical earthen buildings are vulnerable to external solicitations, as earthquakes, tsunamis, environmental conditions and others, and, often, they are under unacceptable risks. For all these aspects, earthen buildings need an indispensable intervention but also an accurate diagnosis to respect the modern restoration principles. Nowadays, the research field related to the structural analysis of existing earthen buildings is very far from a complete and exhaustive knowledge. For studying these types of buildings, experimental investigations are mandatory. The thesis has the ambitious goal to fill the lack of knowledge about the dynamic behavior of historical earthen buildings. The work started with the study of effects of temperature and humidity on the “earth material”. For this reason, single adobe walls were built and analyzed by a continuous monitoring of the internal and external environmental parameters and dynamic properties to understand their behavior as simple adobe construction systems. The main challenges in this stage were the development of a suitable algorithm to automatically identify the dynamic parameters, the study of the internal distribution of temperature and humidity, and, the analysis of the environmental effects on the long-term monitoring of simple adobe systems. The results showed a good heat storing capacity of the walls and the existence of an internal thermal flow connected to a combined effect of air temperature, wind, solar radiation, and wall orientation. Furthermore, environmental seasonal and daily effects were first identified and subsequently isolated from the structural response, demonstrating a clear inverse relationship between temperature and dynamic properties. After this first stage, the application of the achieved knowledge was applied to a real case study to verify the obtained results in a larger scale. The Church of San Pedro de Andahuaylillas was chosen as case study. This church was built in the sixteenth century and represents a suitable example of historical earthen building. This architecture is one of the most amazing and beautiful example of religious art, solemn testimony of the Andean culture. To this church, a long-term monitoring system was applied for a better understanding of the earthen building behavior. The results indicated that he environmental variable affect the structural behavior at two levels: a seasonal long-term influence was detected as well as a daily short- term one. Seasonal effects caused variations of up to 8% in natural frequencies, and shorter-term influences were also verified causing variations of up 3.8%. Daily results showed a delayed effect of the environmental conditions in the structural response. Finally, multiple linear regression models were developed using the absolute humidity as independent variable to successfully predict the long-term frequency variation of the analyzed case study for structural health assessment purpose.

1. Doctorado

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