Carlos Moutinho

LabVIEW toolkits for output-only modal identification and long-term dynamic structural monitoring

This paper describes the development of computational tools for modal identification and long term dynamic monitoring in LabVIEW environment. These tools mainly consist of two individual toolkits for structural modal identification (SMI) and continuous monitoring (CSMI), respectively. The SMI toolkit implements the frequency domain Peak-Picking (PP) and Enhanced Frequency Domain Decomposition (EFDD) method, as well as the time domain Stochastic Subspace Identification (SSI) techniques. Based on this toolkit, the user can easily develop the whole process of structural modal identification by simply pushing buttons. The CSMI toolkit was conceived for continuous dynamic monitoring excluding manual interaction. It automatically searches the latest output measurements, detects maximum vibration amplitudes and makes statistical treatment of acceleration time series, generates waterfall plots for depicting the frequency component distribution and identifies modal parameters based on automated EFDD technique. The application of these tools is briefly described based on experimental data collected at Pinhão bridge and Coimbra footbridge.

Vandal Loads and Induced Vibrations on a Footbridge

The paper describes a study to characterize intentional human dynamic loads (vandal loads) and their induced effects on a footbridge. A numerical model to characterize the dynamic behavior of the footbridge has been developed, is experimentally validated, and is used to numerically simulate the response induced by groups of pedestrians synchronized at critical bridge frequencies. The vandal load associated with a single pedestrian is characterized and compared with definitions in the literature. The response is then calculated considering the measured load and compared with the measured response to the excitation induced by a single pedestrian or a group with varying dimensions. The definition of a general load model for vandal excitation, including a tentative definition for synchronization is discussed.

Dynamic identification and continuous dynamic monitoring of bridges: different applications along bridges life cycle

Abstract This paper aims at stressing the major role that Dynamic Identification and Continuous Dynamic Monitoring can play in the observation and understanding of the structural behaviour of bridges along the different phases of their life cycle, based on the authors’ experience got at the Laboratory of Vibrations and Structural Monitoring (ViBest) of the University of Porto during the last 20 years. The paper comprehends two initial sections summarising some relevant aspects regarding the evolution observed in terms of excitation devices and instrumentation, as well as in the field of modal identification of large Civil structures. Subsequently, the importance of dynamic identification along bridges’ life cycle (design, construction, commissioning, and service or rehabilitation phases) is illustrated on the basis of relevant case studies, involving several outstanding structures. Lastly, the interest and potential of Continuous Dynamic Monitoring is also emphasised, describing several dynamic monitoring programmes implemented with different perspectives, such as: (i) the vibration serviceability safety checking in lively footbridges; (ii) the evaluation of dynamic effects of traffic loads in roadway and railway bridges and fatigue assessment; (iii) the vibration based damage detection; (iv) or the dynamic monitoring of wind effects on large bridges.

ANALYSIS OF THE VIBRATION LEVELS OF A SLENDER FOOTBRIDGE MEASURED BY A CONTINUOUS DYNAMIC MONITORING SYSTEM

This paper is related to the work involving the numerical and experimental dynamic analysis of a very flexible pedestrian bridge located in Porto. Given the high level of vibrations reported by the users of that structure, the Laboratory of Vibrations and Structural Monitoring (www.fe.up.pt/vibest ) from Faculty of Engineering of University of Porto (FEUP) became interested in this case, following the previous work of this research group in this area of Civil Engineering. In a first stage, the structure is described and the identified dynamic properties are listed. Then, experimental and numerical simulations of several scenarios of pedestrian loads exciting the bridge are presented. Given the “lively” behavior of the structure, it was decided to install a dynamic monitoring system in order to characterize the effective levels of vibration experienced by that structure during long periods of time. The results of the dynamic monitoring are exposed in this paper, which gives reason to the actual existence of complaints from pedestrians.

REDUCING VIBRATIONS IN A FOOTBRIDGE USING A SEMI-ACTIVE TUNED MASS DAMPER

The stress-ribbon footbridge located at the campus of the Faculty of Engineering of University of Porto (FEUP) is a slender structure that connects the main buildings of the university to the students’ canteen. Its dynamic behaviour has been studied over the last few years in several areas of the system dynamics. First, the modal parameters in terms of natural frequencies, damping ratios and modal shapes were identified, and a complex non-linear numerical model of the structure that takes into account the various construction phases was calibrated. Then, a comprehensive study of the analysis of the vibration levels of the footbridge involving either regular and vandal loads was developed. Given the perceptible levels of vibration that often affect that structure, an active vibration control system was implemented for research purposes. Since 2009, a dynamic monitoring system composed of 4 accelerometers and 4 thermal sensors collets time series, enabling the Operational Modal Analysis and the Vibration-based Structural Health Monitoring of the footbridge. In 2013, a Tuned Mass Damper was installed in the context of a research project related to Smart Inertial Vibration Control Systems. At a first stage, this device worked passively, tuned close to the critical natural frequency in terms of proneness to resonant pedestrian loads. More recently, the control system was updated to a semi-active functioning with the objective of increasing the system efficiency. This was done because the footbridge has several critical vibration modes around 2 Hz and only one control device was installed. Using the Phase Control law, it is possible to adjust, in real-time, the vibrating frequency of the inertial mass to the structure frequency, enabling not only the correct tuning of the device but also the possibility of performing multimodal control. After a description about how Phase Control works, this paper describes the laboratory tests of the semi-active device, which showed that the system behaved as numerically expected. Then, the implementation of the device in the footbridge is described and all equipment and instrumentation are listed. Finally, the effect of the control system in reducing the vibration levels of the footbridge over the last few years is analysed. This was done by observing the data from the continuous dynamic monitoring system from 2010 until 2016. It was noted a tendency in the reduction of the peak accelerations of some sections of the deck after the installation of the passive TMD, which were even more attenuated after the activation of the semi-active device. 4099 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4099-4114

Dynamic monitoring of civil engineering structures

The paper describes two dynamic monitoring systems installed in civil engineering structures, a footbridge and a suspended stadium roof. These systems are used for characterization of environmental and operational effects and, in the limit, for the early detection of damage. Some examples of collected data and results are presented.

Dynamic monitoring of lively footbridges

The demo will focus on two dynamic monitoring systems installed in footbridges with the purpose of characterizing the dynamic behavior and response of these structures and possibly detecting damage at early stages.

Continuous Dynamic Monitoring of Bridges: Different Perspectives of Application

This paper makes a brief characterisation of some aspects related with the extensive research activity of the Laboratory of Vibrations and Structural Monitoring (ViBest) of the Faculty of Engineering of the University of Porto (FEUP) in the field of Continuous Dynamic Monitoring of Bridges and Special Structures, selecting four examples where large high quality databases have been created since 2007, namely Infante D. Henrique bridge, Pedro e Inês footbride, FEUP Campus stress-ribbon footbridge and Trezói railway bridge.