Two monuments in Portugal are being monitoring by the University of Minho: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. Vibration sensors and temperature and relative air humidity sensors are installed in the two monuments. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures as a part of a heath monitoring process to preserve the historical constructions. The paper presents all the preceding dynamic analysis steps before the monitoring task, which includes the installation of the monitoring system, the system identification and subsequent FE model updating analysis, the automatic modal identification and the investigation of the influence of the environment on the identified modal parameters.
This paper describes the behavior of single rigid-block structures under dynamic loading. A comprehensive experimental investigation has been carried out to study the rocking response of four blue granite stones with different geometrical characteristics under free vibration, and harmonic and random motions of the base. In total, 275 tests on a shaking table were carried out in order to address the issues of repeatability of the results and stability of the rocking motion response. Two different tools for the numerical simulations of the rocking motion of rigid blocks are considered. The first tool is analytical and overcomes the usual limitations of the traditional piecewise equations of motion through a Lagrangian formalism. The second tool is based on the discrete element method (DEM), especially effective for the numerical modeling of rigid blocks. A new methodology is proposed for finding the parameters of the DEM by using the parameters of the classical theory. An extensive comparison between numerical and experimental data has been carried out to validate and define the limitations of the analytical tools under study. Discrete element methodDEM can be considered as a method for modeling discontinuous media. This analysis technique allows relative motion between elements, which is especially suitable for problems in which the
This paper presents the results of the LNEC-3D shaking table tests on two mock-ups, Brick House and Stone House, carried out in the scope of the workshop "Methods and challenges on the out-ofplane assessment of existing masonry buildings". The mock-ups have a U shape with one façade wall and two orthogonal sidewalls. The façade has a central opening and a gable on top, whereas the two sidewalls, acting as abutments, are either blind or have a window. A unidirectional seismic action, in the perpendicular direction to main wall, was applied. Out-of-plane behaviour of the façade was found, even if the response was clearly influenced by the presence of the window in one of the sidewalls, which led to significant torsion of the structure. The detailed description of the two tests and the conclusions are presented. The response of the mock-ups was evaluated based on the displacements, damage and collapse mechanisms developed as function of an increasing intensity earthquake testing protocol, in which a pre-processed strong ground motion component of the Christchurch (New Zealand) earthquake (February 21 st , 2011) was used. IntroductionThis paper focuses on the experimental study of the out-of-plane behaviour of masonry structures under seismic loading and provides a ground for the validation of the different approaches currently available for assessment of existing structures. For that purpose, tests were carried out in the LNEC-3D shake table with two mock-ups: one built using regular clay brick masonry with English bond and the other built using multi-leave granite stone masonry. The mock-ups have a U shape with one façade wall and two orthogonal sidewalls. A unidirectional seismic action perpendicular to main wall was applied. Several experts were invited to predict the out-of-plane seismic capacity prior to the disclosure of the test results, in what is commonly known as a blind prediction test.The main goal of the exercise was to promote a debate about the challenges of existing methods for the out-of-plane assessment of existing masonry buildings, leading to the definition of research needs, rather than evaluating the quantitative differences between the numerical predictions and the experimental results. Each participant was allowed to define the main control outputs according to the structural analysis method adopted, such as the collapse peak ground acceleration, ultimate displacement or energy dissipation.A qualitative assessment was carried out with the purpose of identifying the trends in the predictions of the damage patterns and collapse mechanisms, which allow highlighting the pros and cons of the different methods, discussing their applicability for engineering assessment of existing buildings and comparing the different results with blind experimental tests. To this end, a reference response spectrum and some basic mechanical properties were supplied to the participants, while a clear indication of the performance levels reached and corresponding response spectrum scaling factors had to be indicated b...
This paper describes the dynamical behavior of free standing block structures under seismic loading. A comprehensive experimental investigation has been carried out to study the rocking response of four single blocks of different geometry and associations of two and three blocks. The blocks, which are large stones of high strength blue granite, were subjected to free vibration, and harmonic and random motions of the base. In total, 379 tests on a shaking table were carried out in order to address the issues of repeatability of the results and stability of the rocking motion response. Significant understanding of the rocking motion mechanism is possible from the high quality experimental data. Extensive experimental measurements allowed to discuss the impulsive forces acting in the blocks and the three-dimensional effects presented in the response.
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