P. Galvín

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.

Soil–structure interaction effects on the resonant response of railway bridges under high-speed traffic

In the present contribution, the dynamic behaviour of beams traversed by moving loads including soil–structure interaction (SSI) is investigated. The main application of the study is to analyse the effects of SSI on the resonant response of bridges caused by railway traffic. As this phenomenon is highly influenced by the free vibration response of the deck, a numerical investigation is carried out by analysing the effects of the wave propagation problem on the transverse-free vibration response of beams under moving loads in a wide range of velocities. To this end, a coupled three-dimensional boundary element-finite element model formulated in the time domain is used to reproduce the soil and structural behaviour, respectively. A subset of bridges is defined considering span lengths ranging from 12.5 to 25 m and fundamental frequencies covering associated typologies. A homogeneous soil is considered with shear wave velocities ranging from 150 to 365 m/s. From the single load-free vibration parametric analysis, conclusions are derived regarding the conditions of maximum free vibration and cancellation of the response. These conclusions are used afterwards to justify how resonant amplitudes of the bridge under the circulation of railway convoys are affected by the soil properties, leading to substantially amplified responses or to almost cancelled ones, and numerical examples are included to show the aforementioned situations.

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 ...

A Comparison of Predicted and Measured Ground Vibrations due to High Speed, Passenger, and Freight Trains

In March 2008, the SNCF has launched a blind prediction test for for railway-induced ground vibration. The aim was to compare predictions from different numerical models to measured ground vibrations at a site along the LGV Atlantique and a site along the Paris-Bordeaux line. Apart from vibration measurements, SNCF has also performed tests and collected data for the determination of the input parameters of the prediction models. Based on these input parameters, the free-field vibrations have been predicted by means of a numerical model that has been developed at K.U.Leuven. This model takes into account the dynamic interaction between the train, the track and the soil. The track geometry is assumed to be invariant with respect to the longitudinal direction, allowing for an efficient numerical solution of the dynamic track–soil interaction problem in the frequency-wavenumber domain. Although a good qualitative agreement has been obtained between the predicted and measured vibration velocities, the ratio between the predicted and measured running RMS values of the vibration velocity is sometimes as high as 3 or 5.

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.

Experimental Analysis of Arroyo Bracea II Bridge in Madrid – Sevilla High-Speed Railway Line: Dynamic Response of the Structure and Effect of Soil Properties

Traffic induced vibrations in railway bridges has become an issue of main concern among scientists and engineers due to the extensive construction of new High-Speed railway lines and the upgrading of existing lines for higher operating velocities [1, 2]. In this context, short to medium-span bridges (10–25 m) composed by simply-supported elements are especially critical, due to their usually associated low masses, and may experience considerably high vertical acceleration levels at the platform area [3]. As a result, the transverse acceleration in such structures is one of the most demanding Serviceability Limit States according to present regulations [4]. As a consequence, there is a need to realistically predict the behavior of railway structures in the design phase and along the bridge’s life. In this contribution the authors include results and conclusions from an experimental and numerical analysis of Arroyo Bracea II railway bridge, located in the Madrid-Sevilla High-Speed railway line in Spain. This structure is monitored due to its short length and typology, which make it susceptible to experience high transverse vibration levels. During the experimental campaign the soil properties at the site were obtained. Also, the response of the structure under the circulation of railway convoys travelling at speeds over 260 km/h was measured at several points of the deck and at the abutments. From the experimental measurements the modal parameters of the bridge are identified. Finally the experimental results are compared to those provided by a finite element numerical model in the time and frequency domains. Conclusions are extracted regarding the structure performance and the adequacy of the numerical model implemented for the particular soil and loading conditions.

A SSI NUMERICAL MODEL FOR LAYERED SOILS USING A BEM-FEM FORMULATION IN TIME DOMAIN

Abstract. This paper presents a numerical method based on a three dimensional boundary element-finite element coupled formulation in the time domain. The proposed model allows studying soil-structure interaction problems. The soil is modelled with the boundary element method, where the radiation condition is implicitly satisfied in the fundamental solution. Layered half-space Green’s function including internal material damping is considered as the fundamental solution because of the influence of soil stratification on soil-structure interaction problems is large. This fundamental solution is computed from the exact expressions for the response in the underlying half-space and from a modal solution for the layers. The finite element method is used to represent the structure. In this paper the proposed method is validated by comparison with analytical and numerical results, and an experimental study is done. Afterwards, the dynamic behaviour of a building subjected to an incident wave field is studied.

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.