Mario Solís

Monitoring the Mechanical Behavior of the Weathervane Sculpture Mounted Atop Seville Cathedral’s Giralda Tower

This article presents the application of monitoring and detection of structural damage techniques to a historic monument. Seville cathedral’s famous bell tower ‘La Giralda’ is 96 m tall and is crowned with a large 16th century sculpture known as ‘Giraldillo’. The sculpture is supported with an internal bar structure, which is fitted over the axis about which it rotates according to the wind direction, allowing it to function as a weathervane. Between 1999 and 2005 the Giraldillo was demounted and underwent an intensive restoration process, which included mechanical and structural repair work. As the sculpture is only accessible by means of complex and costly scaffolding systems, an instrumentation system consisting of different types of sensors was installed to study the assembly’s mechanical response, its functioning as a weathervane and its state of conservation while it was being remounted atop the Giralda Tower. Different damage detection techniques aimed at detecting possible deterioration in the Giraldillo’s support structure were employed as well. This article presents results obtained in 2 years of system operation, showing how structural heath monitoring techniques can be applied to historical monuments.

Dynamic characterisation of wind turbine towers account for a monopile foundation and different soil conditions

The response of wind turbines is induced by dynamic loads such as wind, transient and cyclic loads, and also extreme loads such as earthquakes. Thus, the structural design requires an accurate evaluation of the modal parameters of the system because it is strongly required that no resonances are excited. Moreover, it has been concluded from previous research works that soil–structure interaction (SSI) should be accounted for the analysis. In the present paper, the structural dynamic response of wind turbine towers is investigated considering different soil conditions using a numerical model. This research is focused on SSI effects. Firstly, changes in the modal parameters of three different wind turbines considering the effect of three soils are evaluated. The results show that the evaluation of the natural frequency and the resulting classification of the wind turbine design type can be affected by SSI. The obtained results could be used to evaluate the decrement of the natural frequency of the wind turbine account for the soil and the foundation in relation to the frequency computed without soil interaction. Next, the seismic response of the wind tower is analysed considering two seismic events: a horizontally polarised shear incident wave and El Centro earthquake.

Analysis of stationary roving mass effect for damage detection in beams using wavelet analysis of mode shapes

One of the main challenges in damage detection techniques is sensitivity to damage. During the last years, a large number of papers have used wavelet analysis as a sensitive mathematical tool for identifying changes in mode shapes induced by damage. This paper analyzes the effect of adding a mass to the structure at different positions. Depending on the location and severity of damage, the presence of the mass affects the natural frequencies and mode shapes in a different way. The paper applies a damage detection methodology proposed by the authors, although it has been modified in order to consider the addition of the mas. This methodology is based on a wavelet analysis of the difference of mode shapes of a damaged and a reference state. The singular behavior of a normalized weighted addition of wavelet coefficients is used as an indicator of damage. The presence of damage is detected by combining all the information provided by mode shapes and natural frequencies for different positions of the roving mass. A continuous wavelet transform is used to detect the difference between the response of a healthy state and a damaged one. The paper shows the results obtained for a beam with different cracks. The paper analyzes the sensitivity to damage of the proposed methodology by considering some practical issues such as the size of the crack, the number of measuring points and the effect of experimental noise.

Teaching Structural Analysis through Design, Building, and Testing

AbstractThis paper presents the results of an innovative teaching experience in the area of structural analysis in the mechanical engineering program of the Universidad de Sevilla, Spain. The teaching methodology used is aimed at motivating students to learn by promoting the design, calculation, building, and testing of structures. This method not only trains students to make calculations, but also develops skills that allow them to understand how structures function. The project includes subjects taught in the third and fifth year of the course. In their third year, students begin their structural training studying structural analysis, where they learn the basics by designing, building, and testing balsa wood structures. Students have access to computer software when optimizing the design of their models before building and testing them in the laboratory. After this first approach to structural analysis, students receive training on more advanced concepts. A few examples of such concepts are the dynamic ...

Wavelet Based Mode Shape Analysis for Damage Detection

Many authors have proposed wavelet analysis as an efficient and useful numerical tool for damage detection in structures. Some of these proposals consist of the application of the wavelet analysis to the mode shapes of the structure in order to detect perturbations induced by damage. Some authors have proposed the so-called hybrid methods, in which the wavelet analysis is applied to the spatial evolution of a modal damage detection parameter. With these hybrid methods, the ability of the wavelet analysis to detect singularities and variations of a signal is used to enhance the sensitivity of the damage detection parameter. This paper presents a hybrid method based on the variation of mode shapes weighted with the variation of their natural frequencies due to the presence of damage. A Continuous Wavelet Transform is applied to each of the weighted mode shape difference between the undamaged and the damaged state, and the corresponding coefficients for each mode shape are added up. The paper includes an experimental analysis of the sensitivity of the method for a steel beam.

Structural Analysis of La Giralda's 16th-Century Sculpture/Weather Vane

This article presents an analysis of the mechanical behavior of a historical sculpture known as El Giraldillo, which, in addition to its ornamental qualities, also functions as a weather vane. The 4-meter-high bronze sculpture has crowned La Giralda, the bell tower of the cathedral of Seville, since 1568. The mechanical behavior of the sculpture/structure must clearly be analyzed before undertaking its restoration to guarantee that it is capable of withstanding the mechanical actions to which it will be subjected, including self-weight, wind action, thermal effects, and seismic agitation. The analysis was conducted by studying the objects current state of preservation with the aid of a finite element numerical model. The most significant results of this analysis are presented in this article.

Structural Evaluation of an Earthen Building from Operational Modal Analysis

This paper evaluates the structural behavior of a nineteenth century historical construction of rammed earth built in Lima (Peru). The dynamic response of the building was experimentally analyzed from Operational Modal Analysis tests. A FE model was built in order to approach the experimental behavior. Manual calibration of material properties and interaction with surrounding buildings were considered in order to achieve this goal. Due to the complexity of the structure, the level of damage and possible non-linear effects, only the first two modes were considered to be clear enough for calibration purposes. The building is a three story construction made of adobe masonry and a traditional composite material made of wood, cane and mud known as “quincha”. Experimental and numerical results evidenced the different behavior of the quincha and adobe walls in terms of flexibility. Moreover, loss of connectivity or stiffness between floors and walls is observed from the relative displacements between different parts of the building. The paper contributes to the application of vibration based structural health monitoring techniques to earthen historical constructions.

Enhanced Modal Wavelet Analysis for Damage Detection in Beams

The wavelet transform has proven to be a useful mathematical tool to detect changes in the mode shapes of a structure and therefore to detect damage. The authors have proposed a damage detection methodology based on the wavelet analysis of the difference of mode shapes corresponding to a reference state and a potentially damaged state. The wavelet coefficients of each mode shape difference are added up to obtain an overall graphical result along the structure. The coefficients are weighted according to changes in natural frequencies to emphasize the mode shapes most affected by damage. This paper is focused on the enhancement of the damage sensitivity of the methodology. It presents new results when applying a curve fitting approach to reduce experimental noise effect in mode shapes as well as a interpolation technique to virtually increase the geometric sample frequency of the wavelet transform input signal. The enhanced methodology is applied to experimentally tested steel beams with different crack location and depth. The paper analyses the results when considering different number of measuring points. Successful results are obtained using a small number of sensors and mode shapes.

Crack Location in Beams Using Wavelet Analysis

This paper applies a methodology for damage detection in beams proposed by the authors. The methodology is based on a continuous wavelet analysis of the difference of mode shapes between a damaged state and a reference state. The wavelet transform is used to detect changes in the mode shapes induced by damage. The wavelet coefficients for each mode are added up and normalized to unity in order to obtain a clear and precise damage assessment. A curve fitting approach reduces the effect of experimental noise in the mode shapes. When only a small number of measuring points are available, a cubic spline interpolation technique provides additional “virtual” measuring points. The interpolation technique may also be used when measuring points are not equally spaced. It also serves as a softening technique of the mode shapes when applied, and no curve fitting approach is used in that case. An antisymmetric extension at both ends of the mode shapes is used to avoid the edge effect in the wavelet transform. The paper presents the results obtained for steel beams with an induced crack. Several sizes and locations of the crack have been considered. The paper addresses several issues affecting the accuracy of the proposed methodology, such as the number of measuring points and the effect of the extension, curve fitting and interpolation techniques.