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2003, Sports Engineering
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2014, Procedia Engineering
2006, International Journal of Mechanical Sciences
2014, The Journal of Adhesion
2005, Sandwich Structures7: Advancing with Sandwich Structures and Materials
2011, Proceedings of the 1st International Conference on Structural Health Assessment of Timber Structures SHATIS 2011, Lisbon, Portugal, June 16-17, 2011, pp. 1-14, doi: 10.13140/2.1.1887.9040
Long term laboratory experiments have been set up to measure the time dependant performance of multi-nailed connections. Deformations are noted using manual dial gauges and a datalogger for recording strain-gauge based deformation gauges previously used in short term applications. The strain-gauges are bonded to stainless spring steel to give a direct strain to deformation relationship, these are cost effective measuring systems but compensation will need to be made for the long term drift and creep of the strain-gauges. A 3 storey building in New Zealand has frames and energy dissipating rocking shear walls constructed from laminated veneer lumber (LVL) in 2010. Wall post tensioning, wall shortening, deformation of the energy dissipating devices, floor dynamics, moment rotations and mid span deformations are to be remotely monitored. Preliminary dynamic performance has been tested and verified the operation of the installed GNS accelerometers and allowed the initial dynamic modes to be identified.
1990, Canadian Journal of Civil Engineering
2011, Soil Dynamics and Earthquake Engineering
This paper describes ambient vibration based seismic evaluation procedure of an isolated highway bridge. The procedure includes finite element modeling, ambient vibration testing, finite element model updating and time history analysis. Gülburnu Highway Bridge located on the Giresun–Espiye state highway is selected as a case study. Three dimensional finite element model of the bridge is created by SAP2000 software to determine the dynamic characteristics analytically. Since input force is not measured, Operational Modal Analysis is applied to identify dynamic characteristics. Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are used to obtain experimental dynamic characteristics. Analytical and experimental dynamic characteristic are compared with each other and finite element model of the bridge is updated by changing of material properties to reduce the differences between the results. Analytical model of the bridge after model updating is analyzed using 1992 Erzincan earthquake record to determine the seismic behavior. EW, NS and UP components of the ground motion are applied to the bridge at the longitudinal, transverse and vertical directions, respectively. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of highway bridges. Maximum differences between the natural frequencies are reduced averagely from 9% to 2% by model updating. It is seen from the earthquake analyses that friction pendulum isolators are very effective in reducing the displacements and internal forces.► We determine the seismic behavior of Gülburnu highway bridge using finite element analysis and ambient vibration tests. ► We examine changes in dynamic characteristics of the bridge. ► Changing of the some uncertain parameters decreases the differences between analytical and experimental dynamic characteristics. ► We demonstrate that the ambient vibration measurements are enough to identify the most significant modes of highway bridges.
The COST program exists to strengthen Europe and other countries in scientific and technological research, for peaceful purposes, through the support of cooperation and interaction between European researchers. Timber and wood-based engineered products are important as structural materials, especially in the drive towards sustainable technologies and construction. It is very important to improve the properties of these products, making them more competitive and reliable. Research ensures that wood and wood products are at the forefront of the move to more sustainable construction. The Czech Technical University has built a reputation as a leader in experimental research and it is very appropriate that the Department of Steel and Timber Structures should host this conference. COST Action FP1004, “Enhance mechanical properties of timber, engineered wood products and timber structures” provides a network for learning and development in a range of connected topics. This conference is convened as a forum for Early Stage Researchers to present their work. It brings young and experienced researchers together, to learn from one another and to build networks for future research and development. It actively promotes the COST principles of cooperation and interaction and the organizers hope that this will be instilled in the new generation of researchers. The theme that binds the topics is experimental work. The conferences sessions are: Test Methods; Structural Performance; Composites and Reinforcement; Connections. These are at the heart of COST Action FP1004. Proceedings are a key output for the COST Action in defining current work in Europe. Combined with the network built between delegates, they provide a point of reference from which future collaboration will build.
2014, Conference Proceedings of the Society for Experimental Mechanics Series
The modern tiltrotor is an aircraft capable of efficient hover as well as high-speed forward flight. The large, flexible rotors needed for good hover performance are susceptible to an aeroelastic phenomenon known as whirl flutter in high-speed flight: high rotor inflow and the flexible nature of the rotors will result in negative aerodynamic damping when the tiltrotor is in airplane mode, causing the coupled wing/rotor/pylon system to become unstable. Traditionally, the tiltrotor whirl flutter margin has been increased through the use of thick wings of low aspect ratio, which maximize the stiffness of the wings at the expense of increased structural weight and reduced aerodynamic efficiency. To increase the top speed of tiltrotors, new methods of analyzing and mitigating the whirl flutter phenomenon must be developed. This study focuses on the design and development of a semispan wind tunnel model that permits the testing of whirl flutter stability in a controlled, low-risk environment. The wind tunnel model was dynamically tested in the Penn State Hammond Low-Speed Wind Tunnel. Five configurations were tested for modal damping variations with respect to tunnel speed. Two of these configurations ("Gen-2") were modified versions of the first-generation ("Gen-1") wind tunnel model designed and tested by S. C. Johnson in the 2012-2013 timeframe. Three configurations of an all-new model ("Gen-3") were developed to increase the realism of the test specimen, and included features such as tuned wing modal frequencies, higher-Lock number rotor blades, and blade twist. Most importantly, the Gen-3 models were designed to flutter without the use of an added mass or unconventional center of gravity placement. Gen-3 was developed through the use of an in-house computer code, which generated damping predictions for the wing modes at various tunnel speeds. Model components and support equipment were fabricated in-house by the author, with some components (e.g. those requiring computer-controlled machining) outsourced to local manufacturers. Wind tunnel tests were performed in the Hammond tunnel from October 2014 through January 2015; these tests showed that the experimentally-measured flutter speeds of the Gen-3 models were within 5-7% of the predicted values, with the Gen-3a (untwisted composite blades) fluttering at approximately 101 ft./sec., and the Gen-3b model (twisted composite blades) fluttering at approximately 97 ft./sec. The present work has further validated the feasibility of whirl utter testing at a small scale. The Gen-3 model was able to exhibit whirl flutter without the use of an additional mass, and will permit the testing of devices designed to enhance the whirl flutter margin within the current facility. The techniques used to fabricate the Gen-3 model show potential for introducing features such as blade flexibility and an modular wing root flexure for a wider test regime.
2011, Proceedings of 14th Conference of seismic engineering, ANIDIS 2011
The inelastic torsional response of an asymmetric-plan hospital building is studied. The response of the structure in the time domain was recorded by highly sensitive sensor network, integrated by a data acquisition system. The identification was performed using techniques of modal extraction in the frequency domain (frequency domain decomposition). A calibration process was applied in order to identify a reliable structural model to be used for the seismic vulnerability assessment of the hospital building. In particular, a nonlinear static procedure accounting for mass distribution, higher modes contribution and mode-shapes correlation was proposed for the estimation of the seismic response of irregular buildings. Finally, the influence of lateral force distribution, node control during pushover and accidental eccentricity is investigated.
2013
"To improve the understanding of soil-pile interaction under horizontal dynamic loads and seismic events, a parametric centrifugal study was undertaken. Flexible piles with pile caps of different masses and instrumented with 20 strain gauges on the length of the pile were used for this purpose. The piles were impacted and the resulting displacement and acceleration for different levels of force were measured. The equation of the movement of a beam equivalent to the pile under dynamic loading has been established and all the terms of this equation was determined using the experimental results. The term of inertia was divided into two parts, one related to the mass of the pile and the other related to the mass of the associated soil. The contribution of each term to the equation at different period (or time of) of vibration was illustrated. Distribution versus time of the displacements and the reactions of the soil at any depth were deduced from the profiles of the bending moments by a double integration and a double derivation respectively. Then the dynamic P-y curves or loops were constructed based on these results. The procedures of experimental tests and P-y curves construction are explained and a comparison between static and dynamic P-y curves is also indicated."
2003
Page 1. Vibration and Crack Detection in Gas Turbine Engine Compressor Blades using Eddy Current Sensors by Matthew Lackner BSE, Mechanical and Aerospace Engineering, Princeton University (2002) SUBMITTED TO THE DEPARTMENT OF AERONAUTICS AND ASTRONAUTICS IN PARTIAL FULFILLMENT FOR THE DEGREE OF MASTER OF SCIENCE IN AERONAUTICS AND ASTRONAUTICS AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY AUGUST 2004 © Massachusetts Institute of Technology 2003.
2013
2014, Experimental Mechanics
1982, Engineering Structures
2013, Journal of Composite Materials
2009, Piezoceramic Materials and Devices, NOVA Science publ.
In the presented chapter some theoretical and real-world approaches to design and implementation of aircraft structures smart vibration control on the basis of controlled by feedback and shunted by external circuits power PZT patches are presented. First we consider a problem of vibration reduction in the helicopter rotor blades, more particularly, the features of rotor blade dynamics and approach to ensuring a dynamic similarity between full scale and scaled rotor blade. On the basis of this analysis we deduce the principal requirements to smart vibration control of rotor blades. One of the greatest technical difficulties of rotor blade active vibration damping is the necessity to transmit to a blade the number of high-voltage command signals through the rotated hub. The purpose of our investigation was decreasing a number of control channels at saving good vibration damping efficiency. In the presented study we try to find the optimum type (bimorph or unimorph), places, and sizes of plate-like actuators and sensors attached to a composite spar undergoes the bend and twist load. We also perform a comparative investigation of active and passive (shunted by electric circuit) PZT actuators working modes. On basis of numerical simulation it is shown that passive damping mode is efficient in the high frequency range only. On other hand, at active control the stability of control loop can be lost at some vibrations and feedback parameters. We propose an approach according to which all active controlled PZT patches are driven at narrow frequency band filtering preferentially on a first eigenfrequencies. And all installed shunted passive PZT patches will damp high vibration frequencies, simultaneously rising stability of the control loop. Finally we present some experimental results obtained on the scaled (1/7) rotor.
2012
Abstract A non invasive method to assess bone structural integrity (osteoporosis) in female tibiae is presented, based on in-vivo measurement of bone dynamic characteristic (MDF) by applying vibration excitation in the range of acoustic frequencies, in the form of an acoustic sweep signal. The method has already been successfully applied on metallic structures and composites, including animal bones, and is supported by analytical and arithmetic tool based on model's theory.
2004, Engineering Structures
This paper describes an experimental study of a skew bridge model conducted at the Federal Highway Administration Turner-Fairbank Highway Research Center. The objectives of the experiment are: (1) to perform a pilot study on the design, construction, instrumentation, testing and data processing of a skew bridge model, (2) to provide experimental data to validate a 3D finite element model developed
2012
The role of the engineer in society is to guide the wise use of scarce resources (eg, natural resources, human resources, capital, etc.) in order to sustain and improve the human condition, while minimizing direct or collateral damage to the environment and losses from accidents (casualties, injuries, environmental damage, damage to property, etc.).
2013, Report submitted to Earthquake Commission Research Foundation (Project No. UNI/578), 206 pp, doi: 10.13140/2.1.1168.5448
A great deal of knowledge about the performance of structural systems, such as bridges, can be created using full-scale, in-situ experimentation on existing structures. Full-scale testing offers several advantages as it is free from many assumptions and simplifications inherently present in laboratory experiments and numerical simulations. For example, soil-structure interaction, non-structural components, and nonlinearities in stiffness and energy dissipation are always present in their true form in full-scale, in-situ testing. Thus, full-scale experimentation results present the ground truth about structural performance and indeed provide the ultimate test for both actual constructed systems and laboratory and numerical investigations. The performance evaluated this way can be used for advanced assessment of structural condition, detection of damage, aging and deterioration, evaluation of the construction quality, validation of design assumptions, and also as lessons for future de...
In this study the static and dynamic characteristics of conventional open cell polyurethane (PU), of auxetic (negative Poisson's ratio) and of iso -density foams were analysed. The specimens were produced from conventional gray open-cells polyurethane foam with 30-35 pores/inch and 0.0027 g/cm3 density, by means of process which has been previously defined by the authors. Poisson's ratio measurements were performed under quasi-static conditions using an MTS 858 servo- hydraulic test machine and a video image acquisition system. For the auxetic foams the results suggested similar behaviour to that previously reported in the literature, with significant increases in stiffness during compressive loading, and a signi ficant dependence of the Poisson's ratio on the applied strain. Transmissibility tests, performed in accordance with the ISO 13753 procedure for antivibration glove materials, suggested a strong dependence of the transmissibility on the foam manufacturing par...
1995, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts
2007, International Journal of Solids and Structures
2007, Journal of Aircraft
2014
In Brazil, the study of pedestrian-induced vibration on footbridges has been undertaken since the early 1990s, for concrete and steel footbridges. However, there are no recorded studies of this kind for timber footbridges. Brazilian code ABNT NBR 7190 (1997) gives design requirements only for static loads in the case of timber footbridges, without considering the serviceability limit state from pedestrian-induced vibrations. The aim of this work is to perform a theoretical dynamic, numerical and experimental analysis on simply-supported timber footbridges, by using a small-scale model developed from a 24 m span and 2 m width timber footbridge, with two main timber beams. Span and width were scaled down (1:4) to 6 m e 0.5 m, respectively. Among the conclusions reached herein, it is emphasized that the Euler-Bernoulli beam theory is suitable for calculating the vertical and lateral first natural frequencies in simply-supported timber footbridges; however, special attention should be given to the evaluation of lateral bending stiffness, as it leads to conservative values.
2011, Medical Image Analysis
2014, Earthquake Engineering & Structural Dynamics
2010, Procedia Engineering
2009, Structure and Infrastructure Engineering
2006, Canadian Journal of Civil Engineering
2010, Microelectronics Reliability
2006, Engineering Structures
The most established way of performing experimental modal analysis is to use acceleration or velocity based transducers that lead to the calculation of the displacement mode shapes. However, there are applications where the use of strain measurements makes for a more attractive and interesting option. Strain gauges have been commonly used for static load testing of mechanical products in the aeronautic, automotive and mechanical industry. Moreover, fatigue testing, durability analysis and lifetime prediction has also been a common application where strain gauges are used. This sort of testing is a common part of the product development process, and additional information on product durability and dynamic performance can be assessed by obtaining the modal parameters of the system, while still using the same instrumentation. Moreover, since strain measurements are more directly related to stress, fatigue and failure, strain-based measurement methods can be a good option for structural...
2014, Shock and Vibration