Dynamic characterization, modelling and model updating of a lively footbridge

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.This paper presents finite element analyses, experimental measurements and finite element model updating of a lively footbridge consisting on an arched main span 40m long and several shorter access spans. Firstly, a finite element model of the bridge is created in a commercial CAE software and static and modal response are numerically estimated. Then, experimental measurements using static loading test and ambient vibration tests are performed. Initial finite element model is adjusted to match with the static response by fitting some selected parameters. Modal parameters (natural frequencies, mode shapes and modal damping) are extracted and after that the current finite element model is updated. Among the selected parameters, semi-rigid connections in some joints, concrete Young’s modulus and mass density of the concrete deck (to account on pavement mass) are selected to minimize the differences between numerical and experimental structural response. Sensitivity of the modal response to these parameters is also shown. At the end of the study, good agreement between analytical and experimental results is achieved, revealing the suitability of the entire process

On the estimation of the moving mass of a TMD installed on a lively structure

Producción CientíficaTuned Mass Dampers are devices which can be assimilated to single-degree-of-freedom systems with a certain amount of moving mass, a natural frequency and a damping ratio intended to be installed on lively structures to reduce the contribution of a certain mode to their response. Once placed on the structure, the movement of the mass damper couples to the structural response and determines its properties as an isolated system becomes challenging. The authors have previously presented a methodology to estimate the natural frequency and damping ratio of an SDOF system installed on a structure and not necessarily tuned to a certain mode. It was based on a transmissibility function and, thus, the moving mass could not be estimated. With this work, the authors go one step further and present a novel procedure to estimate the moving mass value by means of the same transmissibility function and two well selected frequency response functions. The methodology is applied to estimate the properties of a real single-degree-of-freedom system placed on a lively timber platform. The results are compared with the mass modification technique to show that the proposed methodology provides better estimations in a more efficient way.Ministerio de Economía, Industria y Competitividad - (project RTI2018-098425)Ministerio de Educación, Cultura y Deporte - (grant FPU16/01339

Serviceability conditions of pedestrian structures using a simplified moving mass model

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.A simple mechanical model for pedestrian loading, consisting on a mass with a single degree of freedom that moves at constant speed along the footbridge, is presented. The footbrigde is modelled using a reduced number of beam 2D finite elements, simply supported at its ends. The dynamic interaction is ensured through direct requirement of contact conditions between the mass and the corresponding interpolated point in the beam. When the beam is massive enought, the results are similar to those obtained with models of mobile forces. However, if the beam is lightweight, the effect of the mass of the pedestrian can be significant, resulting in a more realistic modelling. The coupled model allows to study the interaction between the pedestrian and the structure and the results can be used to estimate by simulation the serviceability conditions of this type of slender structures under pedestrian loading

A procedure to track vibration modes under changing external factors: application to a pedestrian bridge

A low-cost vibration monitoring system has been developed and installed on an urban steel- plated stress-ribbon footbridge. The system continuously measures: the acceleration (using 18 triaxial MEMS accelerometers distributed along the structure), the ambient temperature and the wind velocity and direction. Automated output-only modal parameter estimation based on the Stochastic Subspace Identification (SSI) is carried out in order to extract the modal parameters, i.e., the natural frequencies, damping ratios and modal shapes. Thus, this paper analyzes the time evolution of the modal parameters over a whole-year data monitoring. Firstly, for similar environmental/operational factors, the uncertainties associated to the time window size used are studied and quantified. Secondly, a methodology to track the vibration modes has been established since several of them with closely-spaced natural frequencies are identified. Thirdly, the modal parameters have been correlated against external factors. It has been shown that this stress-ribbon structure is highly sensitive to temperature variation (frequency changes of more than 20%) with strongly seasonal and daily trend

Measurement of acceleration response functions with scalable low-cost devices. An application to the experimental modal analysis

Producción CientíficaOne of the most popular options in the Structural Health Monitoring field is the tracking of the modal parameters, which are estimated through the frequency response functions of the structure, usually in the form of accelerances, which are computed as the ratio between the measured accelerations and the applied forces. This requires the use of devices capable of synchronously recording accelerations at several points of the structure at high sampling rates and the subsequent computational analysis using the recorded data. To this end, this work presents and validates a new scalable acquisition system based on multiple myRIO devices and digital MEMS (Micro-Electro-Mechanical System) accelerometers, intended for modal analysis of large structures. A simple form of this system was presented by the authors in a previous work, showing that a single board with some accelerometers connected to it got to obtain high quality measurements in both time and frequency domains. Now, a larger system composed by several slave boards connected and synchronized to a master one is presented. Delays lower than 100 ns are found between the synchronised channels of the proposed system. For validation purposes, a case study is presented where the devices are deployed on a timber platform to estimate its modal properties, which are compared with the ones provided by a commercial system, based on analog accelerometers, to show that similar results are obtained at a significantly lower cost.Junta de Castilla y León - FEDER (VA095P17 y VA228P20)Ministerio de Ciencia e Innovación y Ministerio de Universidades - FEDER (RTI2018-098425

Control de vibraciones en pasarelas peatonales

En los últimos años se ha construido un gran número de pasarelas peatonales como respuesta a la demanda de nuevas vías de paso en las ciudades. Estas estructuras tienen requisitos constructivos menos exigentes en comparación con otros tipos de puentes, lo cual ha facilitado el desarrollo de diseños con nuevos esquemas resistentes, complicadas geometrías y el empleo de nuevos materiales. En general estas estructuras son esbeltas, ligeras y poco amortiguadas, lo que en ocasiones ha generado problemas de vi-braciones al paso de peatones una vez puestas en servicio. Las normativas actuales son cada vez más sensibles a esta problemática, recomendando diseños cuyas frecuencias naturales deben estar alejadas de los rangos de frecuencia de paso típicos de los peatones y fijando límites de confort en forma de valores máximos de aceleración permitidos, asegurándose así un correcto comportamiento de la estructura. En el presente artículo se analiza esta problemática desde un punto de vista práctico. Para ello se muestran los puntos clave de las normativas y guías de diseño de pasarelas que se pueden encontrar actualmente en la bibliografía, se presentan las técnicas que habitualmente se emplean en el análisis dinámico experimental de estas estructuras, y se comentan las soluciones a las que generalmente se recurre para mejorar su comportamiento dinámico. Por último, se muestran los trabajos llevados a cabo por el Centro Tecnológico CARTIF en colaboración con las Universidades de Valladolid y Castilla-La Mancha en la pasarela peatonal del Museo de la Ciencia de Valladolid. Estos trabajos incluyen: (1) el estudio dinámico de los tres vanos metálicos de dicha pasarela, (2) el diseño e implementación de un amortiguador de masa sintonizado en el vano más sensible a las vibraciones, (3) la implementación de un amortiguador de masa activo utilizando un excitador electrodinámico, y (4) el desarrollo de pruebas para la verificación del estado de servicio de la pasarela. In the last years, a wide number of footbridges have been built as demand response of more direct pathways in cities. These structures have lower building requirements as compared with standard bridges. This circumstance has facilitated the development of new structural design with complex geometries and innovative materials. As a result, these structures may be slender, light and low damped, leading to vibration problems once in service. The current codes take into account this problem, and recommend designs with natural frequencies away from the typical pedestrian pacing rates and fix comfort limits to guarantee the serviceability of the structure.This paper studies this problem from a practical point of view. Thus, the key points of codes and footbridges guidelines are showed, the typical experimental dynamic analysis techniques are presented, and the usual solutions adopted to improve the dynamic performance of these structures are discussed. Finally, the works carried out on the Valladolid Science Museum Footbridge by Centro Tecnológico CARTIF in collaboration with the Universities of Valladolid and Castilla-La Mancha are showed. These works include: (1) the dynamic study of the three steel spans of the footbridge, (2) the design and implementation of a tuned mass damper in the liveliest span, (3) the implementation of an active mass damper using an electrodynamic shaker, and (4) the development of field tests to assess the serviceability of such span

6th International Conference on Mechanical Models in Structural Engineering

Producción CientíficaThis ebook contains the 37 full papers submitted to the 6th International Conference on Mechanical Models in Structural Engineering (CMMOST 2021) held in Valladolid on December 2021

Design and validation of a scalable, reconfigurable and low-cost structural health monitoring system

Producción CientíficaThis paper presents the design, development and testing of a low-cost Structural Health Monitoring (SHM) system based on MEMS (Micro Electro-Mechanical Systems) triaxial accelerometers. A new control system composed by a myRIO platform, managed by specific LabVIEW software, has been developed. The LabVIEW software also computes the frequency response functions for the subsequent modal analysis. The proposed SHM system was validated by comparing the data measured by this set-up with a conventional SHM system based on piezoelectric accelerometers. After carrying out some validation tests, a high correlation can be appreciated in the behavior of both systems, being possible to conclude that the proposed system is sufficiently accurate and sensitive for operative purposes, apart from being significantly more affordable than the traditional one.Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant VA095P17 and VA228P20

PhysEx: A novel procedure to estimate full-rank physical matrices of a structure from an incomplete modal model

Producción CientíficaThis work is devoted to presenting and applying a novel methodology that estimates a linear physical model, represented by full-rank mass, stiffness and damping matrices, capable of replicating the dynamic behaviour of an incomplete modal model. No hypothesis is made with respect to the damping matrix, so the procedure is applicable assuming any linear viscous damping model. It is shown that, if the number of considered modes satisfies a certain restriction with respect to the number of degrees of freedom, the problem has infinite solutions that differ in their exogenous eigenvalues. By controlling their effect on the dynamic behaviour of the model in the frequency range of interest, a proper final solution is obtained. The methodology is applied to a three-degrees-of-freedom discrete model and a discretized cantilever beam. Comparisons are made in both frequency and time domains which reveal that the methodology provides physical models that accurately replicate the dynamic behaviour of the incomplete modal model. Even for complete models, where the solvability condition is not met, the methodology manages to provide meaningful results in some situations. To prove the usefulness of the estimated models, a mass is added on one DOF of both examples to show that they reproduce the same effects as the original modified ones. Finally, in the interests of reproducibility, all models and algorithms presented in this article have been made publicly available.Agencia Española de Investigación - Ministerio de economía, industria y competitividad (project RTI2018-098425)Ministerio de Educación, Cultura y Deporte (grant FPU16/01339

Cálculo directo de la carga crítica de pandeo de pórticos. Parte I

De todas las condiciones de diseño de una estructura de barras, en muchos casos, la condición más crítica consiste en asegurar que bajo cualquier combinación posible de cargas no se produzca inestabilidad por flexión, más cuando la tendencia actual es diseñar estructuras esbeltas con aceros de mayor calidad. Resulta por tanto interesantes contar con un método de cálculo que permita determinar de forma sencilla y precisa el máximo nivel de carga admisible, conocido habitualmente como carga crítica de pandeo. Para ello, se plantea el equilibrio de cada barra en su configuración deformada, bajo hipótesis de pequeñas deformaciones y pequeños desplazamientos (Teoría de Primer Orden), resultando un sistema de ecuaciones diferenciales lineal para cada barra. Para obtener la respuesta no lineal del conjunto es necesario imponer en cada unión compatibilidad de desplazamientos y equilibrio en el nudo, nuevamente en la configuración deformada. El objetivo de este trabajo es desarrollar un método sistemático que permita determinar la carga crítica y el modo de pandeo de cualquier pórtico plano sin necesidad de recurrir a las simplificaciones que usualmente se asumen en planteamientos matriciales o de elementos finitos. Esto permitirá obtener resultados precisos con independencia de la discretización realizada.Peer Reviewe