Failure analysis of the collapse of a raised steel wine tank

As structural damage or even catastrophic collapses are sometimes due to improper design, underestimated design loads or unexpectedly extreme loads, progressive collapse and structural robustness has recently received a great deal of attention, while the number of scientific papers published on the topic has grown considerably. This paper describes an analysis of the failure of a 106 m3 steel raised wine tank belonging to a local wine producer that suddenly collapsed, fortunately without personal injury, but causing significant damage to the company's facilities. The collapse generated the progressive failure of other tanks next to the first one that failed. After several visits to inspect the accident on site, a diagnosis was made to determine the causes. Possible reasons were examined by visual inspections and experimental tests on steel specimens recovered from the collapsed structures, which allowed to determine the mechanical properties and study the fracture surfaces by scanning electron microscopy and micrographs. On the other hand, the load-carrying capacities of the structure were studied by a linear-static finite-element and a nonlinear-static push-over analysis. The collapse mechanism of the system was found to be due to cyclic horizontal loads generated by a pressurized air injection system. The results allowed to conclude that this type of structure is highly vulnerable to horizontal loads and has very little capacity to activate alternative loas paths. The paper also describes a possible solution that could be used to improve the mechanical performance of this structural typology against horizontal loading, based on the lessons learned from the experience

Long-term static and dynamic monitoring to failure scenarios assessment in steel truss railway bridges: A case study

The latest studies on failures in steel truss-type bridge found that they are highly vulnerable to damage and thus prone to potential local or total collapse. Many authors recommend monitoring the critical elements in the existing steel truss-type bridges in real time to anticipate any failures in local members. Although mechanical strain is the most frequently used variable for this purpose, this method also happens to be the most expensive monitoring strategy. This paper describes a case study of failure scenarios assessment in a steel truss-type railway bridge after extensive long-term monitoring conducted by the authors, based on measuring vertical deflections and modal frequencies. The structure has both an isostatic and a hyperstatic configuration, and was assessed by means of a combination of: (i) long-term monitoring results, and (ii) a finite element analysis to simulate several failure scenarios. A sensitivity study of the different failure scenarios has been carried out, identifying those that can be detected. The results are used to define practical recommendations for failure detection by measuring vertical deflections and modal frequencies

Equivalent Frame Model with a Decaying Nonlinear Moment-Curvature of Steel-Reinforced Concrete Joints

A numerical model for the analysis of frame structures that is capable of reproducing the behavior of reinforced concrete (RC) members and steel-reinforced concrete (SRC) members in all steps until collapse by simulating a reduced resistance capacity is presented in this work. Taking into account the solid models obtained in previous research that have been validated by experimental results, moment-curvature graphics were obtained in all steps: elastic, plastic, and post-critical to collapse. Beam models versus 3D models considerably simplified the calculation of frame structures and correctly described both the plastic and post-critical phases. The moment-curvature graph can be used in a simplified frame analysis, from post critical behavior to collapse

Trunk and lower limb muscle activation in linear, circular and spin back kicks

As any martial art, taekwondo can be classified as a specialty that requires high technical skills, such as a fine motor control both in static and dynamic conditions. Practitioners predominantly use kicks with high amplitude in both combat and technique (poomse) modalities. The aim of this study was the knowledge about trunk and lower limb muscle activation according to the type of kick (circular, linear and spin back kick) in the taekwondo technique modality. Twelve healthy and elite male taekwondo athletes voluntarily participated in this study. Surface electromyography (EMG) during maximal isometric voluntary contractions (MVC) and execution of the kicks was bilaterally recorded from rectus abdominis (RA), external and internal oblique (EO and IO), erector spinae (ES), rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius lateralis (GL), in the static phase of the three kicks

FRP Confinement of Stone Samples after Real Fire Exposure

The mechanical properties of stone materials can be severely affected by exposure to high temperatures. The effect of fire on stone buildings could cause irreversible damage and make it necessary to retrofit the affected elements. Particularly, the strengthening of columns by confinement with composites has been widely improved during the last decades. Today, fiber reinforced polymer (FRP) confinement represents a very interesting alternative to traditional steel solutions. This work studied the behavior of cylindrical stone specimens subjected to real fire action and confined by means of CFRP or GFRP jackets, with the aim of assessing the effectiveness of these reinforcement systems applied to a material that has previously been seriously damaged by high temperature exposure. In general, the strengthened samples showed notable increases in strength and ductility. The response seemed to depend basically on the FRP properties and not on the degree of damage that the stone core may have suffered. Finally, the results obtained experimentally were compared with the confinement models proposed by the available design guides, in order to evaluate the accuracy that these models can offer under the different situations addressed in this research.This research was funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018‐101148‐B‐I00. The APC was funded by University of Alicante, grant number VIGROB 212

Estimación de la matriz de mezclas en separación ciega de fuentes indeterminada con un número arbitrario de fuentes

Blind source separation consists on estimating n source signals from m measurements generated through an unknown mixing process of the sources. In the underdetermined case where we have more sources than measurements, we divide the problem into two stages: estimation of the mixing matrix and inversion of the linear problem. This paper deals with the first stage. It is well known that when the sparsity of the sources premise is true, measurements tend to align with the columns of the mixing matrix, so the problem can be formulated as estimating the peaks of multidimensional probability density functions (PDF). In this paper we analyze two different techniques to estimate this peaks: one is to convert the multidimensional PDF into the power spectral density (PSD) of multiple complex sinusoidal signals and use different multidimensional espectral estimation techniques to detect the peaks. The other is to convert the (m − 1)- multidimensional PDF to m − 1 unidimensional projections and estimate the peaks of these

El uso de las biografías en la didáctica de las ciencias sociales en educación primaria a través de diferentes metodologías

Con este Trabajo de Fin de Grado se pretende investigar cómo las biografías pueden ayudar a los maestros a llevar a cabo una óptima Didáctica de las Ciencias Sociales en la etapa de Educación Primaria utilizando diversas metodologías basadas en el aprendizaje cooperativo, como pueden ser el Juego-Concurso, el Jigsaw o Rompecabezas, metodología Indagadora y metodología basada en la Narración. Para realizar esta investigación se ha llevado a cabo un estudio de caso en el que se ha trabajado con cuatro grupos de alumnos del mismo curso. Después de haber desarrollado este estudio en el aula, se han obtenido una serie de datos que se han analizado posteriormente. Tras el análisis de los datos obtenidos en el estudio, se han extraído unas conclusiones. Con dichas conclusiones obtenidas se pretende aportar a la Didáctica de las Ciencias Sociales una posible mejora de su praxis a los maestros, o una futura base de investigación sobre el tema

Textile Reinforced Mortars (TRM) tensile behavior after high temperature exposure

Although one of the main advantages of Textile Reinforced Mortars (TRM) is their non-combustible character, their behavior against fire or high temperatures has not been sufficiently studied at present. This work analyzes the behavior of different commercial systems containing inorganic mortars and fabric reinforcements based on glass, carbon and basalt fibers, subjected to different temperature levels. To characterize the mechanical response of the different systems, non-destructive tests have been carried out to determine the dynamic modulus of elasticity of the different materials, and subsequent destructive tests to determine their strength and stress-strain relationship. For this purpose, the TRM coupons have been subjected to uniaxial tensile tests and the deformations have been monitored using LVDT (Linear Variable Displacement Transducer) sensors and DIC (Digital Image Correlation), in order to evaluate cracking patterns and failure modes. The results show, in general terms, that the mechanical capacity of these materials is seriously compromised at temperatures in the order of 400 to 600 °C, which can easily be reached during a fire inside a building. Therefore, it can be concluded that although these systems are erroneously perceived as fire resistant in many cases, they may require additional protection depending on the specific use for which they are intended.The authors would like to acknowledge Mapei Spain S.A. for the materials supplied in this work. This research has been funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-100

TRM (Textile Reinforced Mortars) sometidos a temperaturas elevadas: análisis de la adherencia sobre muros de ladrillo

Uno de los aspectos más importantes que determina la eficacia de los Textile Reinforced Mortars (TRM) es su capacidad de adherencia respecto del sustrato base, cuestión esencial para garantizar una correcta transmisión de tensiones. Aunque este tema ha sido objeto de diferentes investigaciones durante la última década, la adherencia bajo el efecto de temperaturas elevadas apenas ha sido analizada hasta la fecha. En este trabajo se plantea el estudio experimental de la adherencia entre muros de ladrillo cerámico y distintas soluciones de TRM, con mallas de fibras de carbono o vidrio y diferentes matrices. Los ensayos se realizan a temperatura ambiente y tras exposición a 200 y 400 ºC, a fin de evaluar la incidencia que un eventual incendio podría tener en un edificio reforzado con estos materiales. Los resultados muestran, en líneas generales, que la exposición a temperaturas elevadas reduce notablemente la adherencia y puede comprometer seriamente la eficacia de estos refuerzos. Puede concluirse, por tanto, que aunque los TRM se perciben con frecuencia como sistemas resistentes al fuego y que pueden emplearse sin protección, en realidad no es así.Esta investigación ha sido financiada por el Ministerio de Ciencia, Innovación y Universidades, a través del proyecto RTI2018-101148-B-100