Egusquiza, M.; Egusquiza, E.; Valentin, D.; Valero, M.; Presas, A. Engineering failure analysis Vol. 81, p. 234-244 DOI: 10.1016/j.engfailanal.2017.06.048 Data de publicació: 2017-11 Article en revista
In this paper, an uncommon failure of a Pelton turbine has been analyzed. After the monitoring system detected a sudden increase in the vibration levels, the turbine was inspected. The inspection showed that a fragment of one bucket broke off during operation. Moreover there were several buckets with cracks, always located in the same side of the buckets. An analysis of the detached fragment revealed a fatigue problem.After the damage was found, the vibration signatures measured by the monitoring system before damage, with damage and after repair, were analyzed. Before damage occurred, an excessive axial vibration and the excitation of several natural frequencies of the turbine were detected in the measured vibration.In order to identify the origin of the problem the first task was to analyze the dynamic response of the turbine. A numerical model of the runner using the finite element method (FEM) was done. Experimental research using modal analysis techniques (EMA) was also carried out in the turbine runner. The results of the numerical model were compared with the experimental results obtained. With the validated numerical model natural frequencies and mode-shapes were determined and studied.The next step was to determine experimentally the influence of the mounting conditions on the runner dynamics and the transmissibility of the runner vibrations to the machine bearings where the monitoring sensors are located.From the results of this study it was concluded that the natural frequencies excited during machine operation had axial mode shapes indicating that axial forces were applied to the runner. In a Pelton turbine, this can only be produced by a misaligned jet.To determine the influence of a misaligned jet on the bucket stresses, the dynamic behavior of the runner was performed. The dynamic force of the water jet was applied to the runner bucket. The results showed that with a misaligned jet the dynamic stress distribution increases in one side of the bucket with a maximum stress located where the cracks appeared.
The paper presents an integrated approach aimed at assessing the seismic safety of Mallorca cathedral. This cathedral is an extraordinary historical construction dating back to the middle-ages. The experimental modal parameters of the cathedral were identified using Ambient Vibration Testing (AVT). The cathedral numerical model was updated using the identified modal parameters. This updated model was then used to study the seismic response of the cathedral using non-linear static (pushover) analysis. A sensitively analysis was carried out to reveal the dependency of the seismic capacity on the input materials properties. To assess the seismic performance and the safety of the cathedral, the N2 method was employed. It was found that the cathedral is safe when subjected to the earthquakes expected in Mallorca Island.
Failures in reciprocating internal combustion engines operating with landfill gas are not uncommon. In general, damage is located in the combustion chamber surfaces and in the ring grooves, where a layer of non-volatile
combustion products is deposited. These deposits attached to the surfaces reduce heat transfer and increase inner temperature, which produces a knocking phenomena damaging the crank bearings and fusing of the piston head
material. Lubrication problems also appear due to the formation of a layer of soft paste silicone deposits in the rings grooves, which increases friction losses and accelerates wear on cylinder and rings.
In this paper, some typical examples of damaged engines are presented. The deposits found were analysed using Scanning Electron Microscope and Energy Dispersive X-ray Spectroscopy (SEM–-EDX). Additionally, the
engine oil used was also analysed by Infra-Red Spectrometry (IR) and the results were compared with known organo-compounds. A method to detect incipient failure caused by organo-compounds contained in landfill gas is
Silica appears in the layers covering the combustion chamber, as well as silicone compound in the top cylinder zone, piston and ring grooves. Damage is associated with siloxanes (organo-silicon compounds) contained in the
landfill gas, which decompose in the combustion chamber, generating silicic acid and formaldehyde under the high temperature conditions throughout the combustion processes.
Identifying the possible causes of existing damage in historical structures is a complex task. Common difficulties are the limited information regarding the history of the construction, the properties of materials and the morphology of structural members. This paper investigates the capability of advanced numerical modelling to address the aforementioned issues and to simulate the damage in complex masonry structures. The case under study is the church of the Poblet Monastery, one of the UNESCO World Heritage Sites in Spain. The
developed finite element model includes the actual-deformed 3D geometry of a selected bay, aiming to consider the important deformation of the structure during the analysis.
Based on the historical survey, the analysis considers different hypotheses to investigate on the possible causes of existing damage: gravitational loading, settlements , past earthquakes and reported structural alterations. The influence of the material parameters on the structural safety is assessed with parametric analysis. Additionally, the parallel use of graphic statics with numerical analysis helps to interpret realistically the structure’s current equilibrium. The applied numerical strategy is effective to understand the causes of the present damage in the structure. The results of the study are useful to make a first diagnosis and are the prelude for future inspection, testing and monitoring activities
The importance of second order effects has been widely studied in slender concrete structures subjected to compressive stresses, although their effects are not generally taken into account in other fields of structural engineering; this is the case of the overall stability of structures flexible supports, as elastomeric bearing pads. In this paper, the collapse in construction of a 24.9 m span precast concrete Y-beam for the light roof of a sports hall is studied. The roof consisted of a series of these beams simply supported at each end by plain neoprene bearing pads. After a worker had climbed up to the last placed element, the element over-turned producing a partial collapse of the light roof. A simplified analysis, without considering second order effects, indicated that there was an over-turning safety factor (OSF) of 2.67. However, a more detailed analysis showed that with the bearing pad arrangement used, rotational stiffness was drastically reduced, causing the second order effects to gain importance. In spite of the OSF the safety of the element is shown not to be adequate. Upon considering the actual flexibility of the bearing and the large rotations, a reduction of the OSF to neutral equilibrium is explained. Sensitivity and probabilistic analyses are conducted in order to investigate the influence of each parameter and the most likely failure cause. A 90° plan rotation of the bearings would increase stiffness, remarkably reducing the second order effects and would achieve an OSF of 3.99 and a reliability index of 7.9.
In Spain, and in the Mediterranean area in general, there is a long tradition of using "terrazzo", prefabricated cement mortar tiles with a polished upper surface as interior flooring in public and private buildings. This flooring technique provides a surface that is mechanically strong, hard and stable in the long-term.Terrazzo flooring has an appreciated appearance of continuity if installed correctly. In addition, the resulting paving can be polished periodically (every 5. years), which makes it highly prized because it can be made to look new again. Today, it is probably the most common interior flooring technique in Spanish buildings. Everyone, including manufacturers, technicians, workers and users, recognize that it is reliable.However, 10. years ago several incidents occurred in which a notable surface area of terrazzo was affected. The incidents raised the alarm about this interior flooring technique. Such occasional anomalies, as well as changes in consumer tastes, have questioned the supremacy of this technique in the flooring product market.This paper analyses in depth the causes of three such incidents that occurred between 1999 and 2001. The author acted as an external expert consultant in these cases. The first building was a public facility for a university research organization. The anomaly appeared during the construction phase, prior to occupation of the building. The second and third buildings are multifamily housing buildings situated in the same district. The anomaly was declared when people first lived in the building.The conclusions indicate that even extensively used techniques that are currently in the mainstream market can be affected by major anomalies if:. -Rigorous technical quality control is not applied at the building site.-Last minute changes on-site are not authorized by those with previous experience.
A tissue machine suffering from Yankee chatter marks has been experimentally investigated. A series of vibration measurements during normal operation at various Yankee speeds on both the creping and the cleaning blade holders have been carried out. The analysis in a frequency range up to 20 kHz has permitted to identify speed dependent frequency peaks and broadband high frequency vibration content on the creping zone. Hence, an experimental modal analysis of the creping blade and holder has been carried out with the machine stopped to identify its natural frequencies. As a result, resonance conditions have been identified due to the gearbox excitation originated by the meshing process. The study of the corresponding mode shapes has permitted to understand the vibration behavior and its relationship with the damage. To solve the problem, the creping blade holder structure has been redesigned to detune the resonances. Since this overhaul, comparable measurements have confirmed a significant reduction of vibrations and high frequency noise. The appearance of chatter marks has been minimized.
Egusquiza, E.; Valero, M.; Huang , X.; Guardo, A.; Jou, E.; Rodriguez, C. Engineering failure analysis Vol. 23, num. ., p. 27-34 DOI: 10.1016/j.engfailanal.2012.01.012 Data de publicació: 2012-02-02 Article en revista
Martinez, A.; Gamez, J.; Sanchez-Soto, M.; Velasco J.I.; Santana, O.; Maspoch, M. Engineering failure analysis Vol. 16, num. 8, p. 2604-2617 DOI: 10.1016/j.engfailanal.2009.04.027 Data de publicació: 2009-12 Article en revista
Historical and heritage buildings have been remodelled lots of times in his large history, especially for old private ones. For some years these historical buildings have been used for other public o private uses than the one which were designed. Especially important are the remodelling carried out during the last few decades, using extensively concrete. These changes to adapt and restore the structures were performed in order to develop specific uses and, generally, they are not enough documented.
The modifications made and the changes in the employ of these buildings also alter their structural behaviour, which must be calculated when new functions of the structures are considered. In this way, it is required the knowledge of the structural inner elements. The analysis of this kind of constructions has to preserve the integrity of the old remaining elements. Hence, non-destructive techniques have to be applied in order to determine exactly the old elements, the new ones and to determine the different components of the buildings. Now a day, high frequency radar techniques has been enough improved to be use to acquire a high confidentially, accurate and precise information about all these different elements and different parts of the structure.
In this work we present a case study of the high frequency radar techniques applied to a S. XV building that was remodelled in several times. The last change was carried out during the 60 decade of the last century. In this arrangement, it is supposed that almost all the floors were replaced by a beam-flooring blocks structure. The GPR data obtained in the survey allow determining the specific zones affected by this last remodel work that affects mainly the floors of the first and second level of the building. It was also possible to determine the typology of the constructive elements and pieces, detecting some of the bars inside the beams. We also have detected some oldest structural change and the adopted solutions. Finally, results allow us to separate the different zones of the building depending on the structural elements supporting the floor.
Traditional architectonic heritage elements are fragile and irreplaceable resources, signs of the ancient ways of life and
the history of the modern societies, and essential valuable elements of the own landscape of a region. Accurate updated
documentation might be the basis for any conservation or restoration intervention over architectonic heritage in order
to ensure the conservation in its original appearance and in a collapse risk-free state, with the minimum intervention.
This paper shows a multidisciplinary approach to heritage documentation involving close range photogrammetry and ground penetrating radar techniques, as well as the development of finite elements based structural models. Specifically this
study is focused on the documentation of a mediaeval bridge concerning the geometric shape, the building material and the
current damages and its causes. The usefulness of close range photogrammetry techniques in the accurate 3D modelling,
cracks detection and mapping and exterior material characterization is analyzed. Further, a non-destructive test through
GPR is employed for the interior material and zones description. For both techniques, the methodology followed for data
collection and data processing aimed at minimisation of time consuming and optimisation of results is described in detail. Advantages and limitations of these techniques are displayed and the accuracy of the obtained results is also estimated.
Resulting information related to the whole bridge geometry is taken as basis to develop a numerical analysis using the finite elements methods (FEM). Linear finite analysis provides useful information for diagnosis although non-linear methods
should be used when the properties and geometry of the internal and external elements are well known. Photogrammetry
provides the exact geometry needed to perform the FEM pre-process. Radar data provide approximate information about the different internal zones of the bridge. Finally, the FEM analysis leads to obtain a stress distribution compatible with the detected damages, allowing identifying its possible causes. Close range photogrammetry, ground penetrating radar techniques and the FEM analysis are proposed to perform a
complete survey of the stability of the bridge and its accurate geometry.
Otárola, T.; Hollner, S.; Bonnefois, B.; Anglada, M.; Coudreuse, L.; Mateo, A. Engineering failure analysis Vol. 12, num. 6, p. 930-941 DOI: 10.1016/j.engfailanal.2004.12.022 Data de publicació: 2005-12 Article en revista