Ultrasonic Pulse-Echo Signal Analysis for Damage Evaluation of Metallic Slit-Plate Hysteretic Dampers

This paper proposes a pulse-echo Ultrasonic Testing (UT) methodology to quantify the damage of hysteretic dampers subjected to cyclic loadings. Energy dissipation is known as an innovative strategy for the protection of buildings against earthquakes. It consists of installing special devices called dampers in the construction, which are entrusted to dissipate most of the energy input by the earthquake, thus keeping the main structure basically undamaged. In particular, the hysteretic dampers dissipate the input energy through plastic deformations in their metallic parts. Several moderate ground motions would not exhaust the capacity of the dampers, but they cause damage—plastic deformations in the device. Therefore, continuous or periodic inspections of the damper are required in order to decide upon its eventual replacement. In this particular work, several hysteretic dampers made of stainless steel were subjected to different patterns of low-frequency cyclic loads that caused diverse levels of damage. Each damper underwent pulse-echo UT before and after the cyclic loading. Spectral energy of the echo signals was properly calculated at each damage level in order to define a reliable damage index. The new index has been compared with a well-established mechanical damage index, ID, previously proposed by the authors. A successful correlation was observed, making the pulse-echo UT technique promising for this particular application.This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429

Acoustic emission as a reliable technique for filiform corrosion monitoring on coated AA7075-T6: Tailored data processing

Acoustic emission (AE) was used for in-situ filiform corrosion (FFC) monitoring on coated AA77075-T6. The analysis of AE data using DBSCAN as clustering algorithm (validated by Bhattacharyya Coefficients´ evaluation) has revealed the presence of three clusters (out of four) related to phenomena involved in the FFC mechanism: metal-coating interface delamination due to opening (tensile), sliding (shear) and mixed mode enclosing both previous ones. The peak frequency was found to be the most relevant descriptor for clustering by using Random Forest classifier, and the correlation with the dominant frequencies range was validated obtaining the Power Spectrum Density of the AE signals.This work has been funded by the European Commission under the Horizon 2020 framework (H2020-CS2-CFP09-2018-02) within the U-Cross project (Grant Agreement 864905) in collaboration with Dassault Aviation, INSA Lyon, Mistras Group, Titania Ensayos y Proyectos Industriales and Université Bourgogne-Franche-Comté. J.M. Vega also would like to acknowledge the support of RYC2021-034384-I by Ministerio de Ciencia e Innovació

Pine Beams Retrofitted with FRP and Poplar Planks: Mechanical Behavior

The paper presents an experimental analysis of the bending behavior of pine beams (Pinus Sylvester) retrofitted with fiber reinforced plastic (FRP) and poplar planks used as external covering. Poplar wood was chosen because of its rapid growth in planted forests, its homogeneity and attributes for sustainable local development, and high CO2 absorption rate. Vibration tests were also conducted in order to evaluate the stiffness in a non-destructive way and compare it with that obtained by means of the destructive tests. Three types of reinforcement were compared, namely: basalt fabric (FB), carbon fabric (FC) and carbon laminate (LC). In addition, some pine beams were reinforced only with poplar planks and used as control specimens in order to evaluate the improvement provided by the FRP. It was observed that a strong delamination preceded the final breakage of beam. Moreover, the results indicated that stiffness is provided mainly by the poplar plank and not by the FRP, as was expected.This work was made possible thanks to the financial support of the COMPOP_Timber project “Desarrollo de productos de ingeniería elaborados a base de tablones y chapas de chopo con inserciones de material compuesto para su uso en construcción”, BIA2017-82650-R

Temporal Acoustic Emission Index for Damage Monitoring of RC Structures Subjected to Bidirectional Seismic Loadings

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs.This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429, by the Spanish Ministry of Economy and Competitivity, research project reference MEC BIA2017 88814 R and received funds from the European Union (Fonds Européen de Dévelopment Régional)

Monitorización mediante técnicas vibro-acústicas de estructuras sismorresistentes de hormigón armado sometidas a cargas dinámicas en mesa sísmica

En zonas de sismicidad moderada o alta, como el sur de Europa, los terremotos causan la pérdida de vidas humanas y tienen un impacto económico importante. Las pérdidas humanas se han reducido notablemente en las construcciones proyectadas siguiendo normas modernas. Sin embargo, el control/reducción de los daños sigue siendo una asignatura pendiente. En particular, en esta Tesis Doctoral se exponen los trabajos y resultados experimentales relacionados con el diagnóstico del daño en estructuras bidireccionales de hormigón armado (HA) y en disipadores histeréticos con propiedad de recentrado TTD-NiTi, sometidos a ensayos sísmicos (simulaciones biaxiales) y ensayos cuasi-estáticos, respectivamente. En concreto, se monitorizan las estructuras de HA con el método de emisión acústica (EA) para evaluar el daño en el hormigón, y se inspecciona la parte disipadora del TTD-NiTi con los métodos de ultrasonidos (UT) y memoria magnética del metal (MMM) para evaluar el grado de deformación plástica alcanzado y decidir sobre su eventual sustitución. En ambos casos se proponen nuevos índices de daño indirectos que se validan con índices de daño mecánicos bien establecidos en la bibliografía.In areas of moderate or high seismicity, such as southern Europe, earthquakes cause the loss of human lives and have a significant economic impact. Human losses have been significantly reduced in the constructions designed following modern standards. However, damage control/reduction remains a pending issue. Seismic engineering has been oriented since the beginning of the 21st century to produce structures with controlled damage and quantifiable repair costs, within the so-called Performance Based Seismic Resistance Project (PBSD) paradigm. In particular, this Doctoral Thesis shows the experimental works and results related to the diagnosis of damage in bidirectional reinforced concrete (RC) structures and in TTD-NiTi hysteric dampers with recentering properties, subjected to seismic tests (biaxial simulations) and quasi-static trials, respectively. Specifically, the RC structures are monitored with the acoustic emission method (AE) to assess the level of damage of the concrete, while the dissipative part of the TTD-NiTi is inspected with the ultrasonic (UT) and magnetic memory metal (MMM) methods in order to evaluate the degree of plastic deformation achieved and then decide on its eventual replacement. In both cases, new indirect damage indices are proposed and validated with well established mechanical damage rates in the literature.Tesis Univ. Granada.PE-12 TEP-02429. Proyectos de Excelencia de la Consejería de Innovación, Ciencia y Tecnología de la Junta de Andalucía. Disipadores de energía histeréticos avanzados con propiedades de recentrado y memoria de forma: desarrollo, monitorización del daño y estrategias de implementación en el mercado. Investigadores principales: Amadeo Benavent-Climent y Antolino Gallego Molina. BIA2017 88814 R. Proyectos del Plan Nacional I+D+i del Ministerio de Ciencia, Innovación y Universidades. Estudio numérico y experimental de la respuesta sísmica de estructuras con disipadores de energía híbridos que combinan componentes viscosas y elastoplásticas. Investigador principal: Amadeo Benavent-Climen

Acoustic emission and numerical analysis of pine beams retrofitted with FRP and poplar wood

Acoustic emission (AE) released by pine beams retrofitted with fiber reinforced plastic (FRP) and poplar planks in bending is analyzed. Basalt fabric (FB), carbon fabric (FC), and carbon pultruded laminate (LC) have been used as FRP. Experimental results and AE behavior are discussed based on an elastoplastic finite-element numerical model. The model demonstrates a strong strain concentration at the end of poplar planks, which causes high AE activity in these areas and acts as a precursor of the delamination of the poplar plank. Based on the experimental results, some AE criteria for predicting the onset of the delamination are tentatively proposed. © 2020 by the authors

Experimental validation of a CFRP laminated/fabric hybrid layout for retrofitting and repairing timber beams

This paper proposes a new hybrid layout to retrofit and repair timber beams by means of carbon composite material. It is based on the combination of a carbon laminate strip attached on the tension side, and a carbon fabric discontinuously wrapping the timber element. This layout has been experimentally validated by means of a study involving large-scale timber beams with many years in service. Results demonstrate not only that the bending load capacity of the broken beams can be totally recovered, but that it may even be increased by 70% with respect to the non-broken ones. © 2018, © 2018 Taylor & Francis Group, LLC

Diagnosis of hysteretic dampers used for seismic protection of structures by means ultrasonic measurements

Energy dissipation is an innovative strategy for the passive protection of buildings and infrastructures against earthquakes. It entails installing special devices called dampers in a construction. They dissipate most of the energy input by an earthquake, thus keeping the main structure basically undamaged. Among the different types available, the so-called hysteretic dampers are commonly used to dissipate energy through plastic deformations in metallic parts of the device. Several moderate ground motions or even a single severe earthquake would not exhaust the capacity of the dampers, but they do cause damage —namely, plastic deformations in the device. Therefore, continuous or periodic inspections of the damper are required in order to decide upon its eventual replacement. The present work proposes Ultrasonic Testing (UT) as a method to quantify the damage upon hysteretic dampers subjected to cyclic loadings. To this end, several hysteretic dampers made of stainless steel were subjected to different patterns of quasi-static (low-frequency) cyclic loads that caused diverse levels of damage. Each damper underwent UT before and after the cyclic loading. UT parameters related to ultrasound waves including spectral amplitude and spectral energy were properly analyzed at each damage level. Based on these parameters, a UT damage index is put forth. The proposed UT index was then compared with a well-established mechanical damage index, ID, based on decomposing load–displacement curves into the skeleton part and Bauschinger part and computing the corresponding energies. A successful correlation was observed between the mechanical damage index ID and the novel UT index, making the UT technique promising for this particular application. © 2019 Elsevier Lt

Acoustic emission analysis of raw bamboo subjected to tensile tests

This work presents data analysis of the acoustic emission (AE) signals released by raw bamboo specimens subjected to monotonic tensile tests. Bamboo wood samples were extracted from the full culm of Bambusa Vulgaris species. A spectral analysis of the AE signals was conducted. It was found that the material suffers a significant plasticization before breakage of the culm's inner wall. From this point and until the final breakage of the outer wall, an important increase of the center of gravity (CoG) of the signal spectrum was observed. AE signals with CoG above 200 kHz were associated with fiber breakage. © 2019 Taylor & Francis Group, LLC

Acoustic emission analysis of raw bamboo subjected to tensile tests

This work presents data analysis of the acoustic emission (AE) signals released by raw bamboo specimens subjected to monotonic tensile tests. Bamboo wood samples were extracted from the full culm of Bambusa Vulgaris species. A spectral analysis of the AE signals was conducted. It was found that the material suffers a significant plasticization before breakage of the culm’s inner wall. From this point and until the final breakage of the outer wall, an important increase of the center of gravity (CoG) of the signal spectrum was observed. AE signals with CoG above 200 kHz were associated with fiber breakage. © 2019, © 2019 Taylor & Francis Group, LLC