Vibration serviceability of footbridges under human-induced excitation : a literature review

Increasing strength of new structural materials and longer spans of new footbridges, accompanied with aesthetic requirements for greater slenderness, are resulting in more lively footbridge structures. In the past few years this issue attracted great public attention. The excessive lateral sway motion caused by crowd walking across the infamous Millennium Bridge in London is the prime example of the vibration serviceability problem of footbridges. In principle, consideration of footbridge vibration serviceability requires a characterisation of the vibration source, path and receiver. This paper is the most comprehensive review published to date of about 200 references which deal with these three key issues. The literature survey identified humans as the most important source of vibration for footbridges. However, modelling of the crowd-induced dynamic force is not clearly defined yet, despite some serious attempts to tackle this issue in the last few years. The vibration path is the mass, damping and stiffness of the footbridge. Of these, damping is the most uncertain but extremely important parameter as the resonant behaviour tends to govern vibration serviceability of footbridges. A typical receiver of footbridge vibrations is a pedestrian who is quite often the source of vibrations as well. Many scales for rating the human perception of vibrations have been found in the published literature. However, few are applicable to footbridges because a receiver is not stationary but is actually moving across the vibrating structure. During footbridge vibration, especially under crowd load, it seems that some form of human–structure interaction occurs. The problem of influence of walking people on footbridge vibration properties, such as the natural frequency and damping is not well understood, let alone quantified. Finally, there is not a single national or international design guidance which covers all aspects of the problem comprehensively and some form of their combination with other published information is prudent when designing major footbridge structures. The overdue update of the current codes to reflect the recent research achievements is a great challenge for the next 5–10 years

Fourth Aircraft Interior Noise Workshop

The fourth in a series of NASA/SAE Interior Noise Workshops was held on May 19 and 20, 1992. The theme of the workshop was new technology and applications for aircraft noise with emphasis on source noise prediction; cabin noise prediction; cabin noise control, including active and passive methods; and cabin interior noise procedures. This report is a compilation of the presentations made at the meeting which addressed the above issues

A Novel Experimental Approach Using A Reconfigurable Test Setup For Complex Nonlinear Dynamic Systems

Experimental nonlinear dynamics is an important area of study in the modern engineering field, with engineering applications in structural dynamics, structural control, and structural health monitoring. As a result, the discipline has experienced a great influx of research efforts to develop a versatile and reliable experimental methodology. A technical challenge in many experimental studies is the procurement of a device that exhibits the desired nonlinear behavior. As a result, many researchers have longed for a versatile, but accurate, testing methodology that has complete freedom to simulate a wide range of nonlinearities and stochastic behaviors. The objective of this study is to develop a reconfigurable test setup as a tool to be used in a wide range of nonlinear dynamic studies. The main components include a moving mass whose restoring force can accurately be controlled and reprogrammed (with software) based upon measured displacement and velocity readings at each time step. The device offers control over nonlinear characteristics and the equation of dynamic motion. The advantage of having such an experimental setup is the ability to simulate various types of nonlinearities with the same test setup. As a result, the data collected can be used to help validate nonlinear modeling, system identification, and stochastic analysis studies. A physical test apparatus was developed, and various mechanical, electrical, and programming calibrations were performed for reliable experimental studies. To display potential uses for the reconfigurable approach, examples are presented where the device has been used to create physical data for use in change detection and deterioration studies. In addition, a demonstration is presented of the device’s ability to physically simulate a large-scale orifice viscous damper, commonly used in vibration mitigation in bridges and buildings. For a large-scale viscous damper, physical testing is required to ensure structural design properties. However, due to the large scale of the dampers, expensive dynamic loading tests can be carried out at a very iii limited number of facilities. Using the reconfigurable test setup, the dynamic signature of the large-scale viscous damper can accurately be simulated with pre-collected data. The development of a system capable of emulating the restoring force of a nonlinear device with software is a novel approach and requires further calibration for increased reliability and accuracy. A discussion regarding the challenges faced when developing the methodology is presented and possible solutions are recommended. The methodology introduced by this apparatus is very promising. The device is a valuable experimental tool for researchers and designers, allowing for physical data collection, modeling, analysis, and validation of a wide class of nonlinear phenomena that commonly occur in a wide variety of engineering applications

Space station structures and dynamics test program

The design, construction, and operation of a low-Earth orbit space station poses unique challenges for development and implementation of new technology. The technology arises from the special requirement that the station be built and constructed to function in a weightless environment, where static loads are minimal and secondary to system dynamics and control problems. One specific challenge confronting NASA is the development of a dynamics test program for: (1) defining space station design requirements, and (2) identifying the characterizing phenomena affecting the station's design and development. A general definition of the space station dynamic test program, as proposed by MSFC, forms the subject of this report. The test proposal is a comprehensive structural dynamics program to be launched in support of the space station. The test program will help to define the key issues and/or problems inherent to large space structure analysis, design, and testing. Development of a parametric data base and verification of the math models and analytical analysis tools necessary for engineering support of the station's design, construction, and operation provide the impetus for the dynamics test program. The philosophy is to integrate dynamics into the design phase through extensive ground testing and analytical ground simulations of generic systems, prototype elements, and subassemblies. On-orbit testing of the station will also be used to define its capability

Implications of nonlinear suspension behaviour for feedforward control of road noise in cars

Active control offers a lightweight solution to the problem of low frequency structure-borne road noise in cars. Feedforward control of road noise is predominantly limited by the difficulty of finding reference signals that are highly coherent with the sound in the cabin. One factor that could restrict the coherence of the reference signals, and therefore the performance of a linear control system, is the behaviour of nonlinear components in the suspension. The purpose of this research is to identify potential sources of nonlinearity in a car’s suspension and investigate their influence on the propagation of structure-borne road noise into the cabin. The details of experiments and simulations are described that aim to quantify the role of nonlinearity in the suspension’s dynamics, and determine to what extent it limits the performance of a linear feedforward road noise control system. The results of experiments conducted on a Nissan Leaf test vehicle are presented that establish the theoretical maximum noise reduction that can be achieved with a linear control system using reference sensors placed at the wheel hubs. Laboratory experiments on the components in the Nissan Leaf’s suspension are presented that identify the hydraulic dampers as the main source of nonlinearity in the road noise transmission path. Models of the key components in a car suspension are developed based on the results of the experiments. Models for the front and rear dampers in the Nissan Leaf are validated up to 300 Hz, and analysed to reveal the mechanisms causing their nonlinear dynamics. Models for the bushings, springs and wishbone are developed and combined into a full suspension model. The suspension model’s predictions add to the evidence from the measurements that road noise transmission is strongly influenced by nonlinearity in the damper. Some implications of the suspension’s nonlinear dynamics for feedforward control of road noise are then explored. The linear control systems used currently are often limited to one reference sensor on each suspension; a simplified analysis of a two transmission path suspension system shows that, if one path is nonlinear, a linear control system with a single reference sensor can not cancel all of the noise generated at the wheel. This thesis presents strong evidence that nonlinear suspension dynamics limit the performance of feedforward road noise controllers. A nonlinear model of vibration transmission through a suspension is developed and guidelines are suggested for reference sensor selection.Bose Corporatio

Innovations in earthquake risk reduction for resilience: Recent advances and challenges

The Sendai Framework for Disaster Risk Reduction 2015-2030 (SFDRR) highlights the importance of scientific research, supporting the ‘availability and application of science and technology to decision making’ in disaster risk reduction (DRR). Science and technology can play a crucial role in the world’s ability to reduce casualties, physical damage, and interruption to critical infrastructure due to natural hazards and their complex interactions. The SFDRR encourages better access to technological innovations combined with increased DRR investments in developing cost-effective approaches and tackling global challenges. To this aim, it is essential to link multi- and interdisciplinary research and technological innovations with policy and engineering/DRR practice. To share knowledge and promote discussion on recent advances, challenges, and future directions on ‘Innovations in Earthquake Risk Reduction for Resilience’, a group of experts from academia and industry met in London, UK, in July 2019. The workshop focused on both cutting-edge ‘soft’ (e.g., novel modelling methods/frameworks, early warning systems, disaster financing and parametric insurance) and ‘hard’ (e.g., novel structural systems/devices for new structures and retrofitting of existing structures, sensors) risk-reduction strategies for the enhancement of structural and infrastructural earthquake safety and resilience. The workshop highlighted emerging trends and lessons from recent earthquake events and pinpointed critical issues for future research and policy interventions. This paper summarises some of the key aspects identified and discussed during the workshop to inform other researchers worldwide and extend the conversation to a broader audience, with the ultimate aim of driving change in how seismic risk is quantified and mitigated

Damping Behaviour of Slender Telecommunications Structures

During the last two decades, the development of mobile telecommunications (‘telecoms’) technologies has resulted in an increased number of antennas to be accommodated around us on different kinds of structures. From new, short monopoles to old high guyed masts, all are considered sensitive flexible structures under wind, many of which are required to hold more equipment than their initial design loading capacity. The dynamic analysis of these structures has been neglected for years, in part as it is clearly a field that requires further investigations with new modern methodologies and knowledge. Within the industry, damping is the topic that provides the most uncertainty between existing expert consultants. The complex nature of damping arises from the high deviation between similar structures and the number of involved sources that modify this behaviour, from boundary conditions to aerodynamic effect, or nonlinear amplitude and frequency dependence relationship. In this PhD research, several projects related to response-data acquisition were used to determine how damping behaves for each selected typology structure (monopoles, lattice towers and high guyed masts). Old and new estimation techniques have been applied after human and wind-ambient excitation to provide reliable data to verify current approaches of assessing damping and provide new clues and perspective about understanding damping in this kind of structures. The research counts on a study of the generic structural damping component on short structures compounded by soil-foundation component and material-connection defined by free decaying responses. A study of non-linearities exist on the response that help to determine sources of damping, and finally, diverse studies of monitoring systems under wind excitation were carried out to allow the research to study actual service response to extract aerodynamic damping, and the accuracy of current drag factors for different wind effects. This new perspective provides essential knowledge to structural engineers when designing current and future structures, advising on the effectiveness and feasibility of external damping providers, not just as an option to minimise aeroelastic vortex shedding effects, but also to reduce the buffeting response with the consequential structural capacity improvement. Results also show the deficiency of current standards and recommendations in the estimation of dynamic properties, especially on damping matter

Enhancing the collaboration of earthquake engineering research infrastructures

Towards stronger international collaboration of earthquake engineering research infrastructures International collaboration and mobility of researchers is a means for maximising the efficiency of use of research infrastructures. The European infrastructures are committed to widen joint research and access to their facilities. This is relevant to European framework for research and innovation, the single market and the competitiveness of the construction industry.JRC.G.4-European laboratory for structural assessmen

Aeronautical Engineering: A continuing bibliography, supplement 120

This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980