Full-scale Vibration Tests Research Articles

Probabilistic model updating of steel frame structures using strain and acceleration measurements: A multitask learning framework

This paper proposes a multitask learning framework for probabilistic model updating by jointly using strain and acceleration measurements. This framework can enhance the structural damage assessment and response prediction of existing steel frame structures with quantified uncertainty. Multitask learning may be used to address multiple similar inference tasks simultaneously to achieve a more robust prediction performance by transferring useful knowledge from one task to another, even in situations of data scarcity. In the proposed model-updating procedure, a spatial frame is decomposed into multiple planar frames that are viewed as multiple tasks and jointly analyzed based on the hierarchical Bayesian model, leading to robust estimation results. The procedure uses a displacement–stress relationship in the modal space because it directly reflects the elemental stiffness and requires no prior knowledge concerning the mass, unlike most existing model-updating techniques. Validation of the proposed framework by using a full-scale vibration test on a one-story, one-bay by one-bay moment resisting steel frame, wherein structural damage to the column bases is simulated by loosening the anchor bolts, is presented. The experimental results suggest that the displacement–stress relationship has sufficient sensitivity toward localized damage, and the Bayesian multitask learning approach may result in the efficient use of measurements such that the uncertainty involved in model parameter estimation is reduced. The proposed framework facilitates more robust and informative model updating.

STUDY OF THE INFLUENCE OF METRO LOADS ON THE DESTRUCTION OF NEARBY BUILDINGS AND CONSTRUCTION STRUCTURES USING BIM TECHNOLOGIES

The authors studied the influence of metro loads on the destruction of nearby buildings and construction structures with the help of BIM technologies in order to eliminate the human factor at the design stage. In the study, numerical modeling was carried out using the LIRA-SAPR software package, and dynamic loadings were set by the time integration technique. The suggested technique involved a nonlinear dynamic analysis conducted considering the time factor; the parameters of the stress-strain state (displacement, force, stress) were determined at each moment of exposure, changing the rigid characteristics of the building structures. The authors conducted a structural assessment of an unfinished construction facility, considering the vibrodynamic loads of the metro. Numerous models were adopted as the structural designs of buildings that consider various impact factors, such as nonlinear soil behavior and permanent action and the nature of dynamic loads. The comparison with experimental data confirmed the theoretical and computational parts of the developed technique. The study determined the vibrodynamic impact of the metro on the construction structures. Verification of the developed methodology based on BIM technologies was carried out by comparing the results of numerical experiments with the results of subsequent full-scale vibration tests.

Assessing vibration isolation performance of single and coupled wave barriers through field experiments

Wave barriers have become a common practice in the mitigation of undesired ground vibrations when direct isolation of the source has not been applicable. Even though the vibration isolation performance of open and in-filled trenches has been scrutinized, only a limited number of experimental studies are available about stiff wave barriers such as piles and sheetpiles. The present study aimed at assessing not only the screening effectivenesses of single barriers such as open trench and sheetpile but also the coupled open trench-sheetpile barrier. 15 m long, 0.75 m wide, 3 m deep single open trench and 15 m long, 8 m deep sheetpile were investigated in full-scale vibration tests. The influences of excitation frequency, source-barrier distance and barrier type on the vibration isolation were examined. The efficacy of the single and coupled-wave barriers was quantitatively presented within a wide range of frequencies (10–80 Hz) based on field measurements using highly sensitive accelerometers and geophones. No vibration isolation was provided at the excitation frequency of 10 Hz, while all the wave barriers provided an appreciable amount of reduction in the amplitudes of the vibrations at other frequencies. In most of the test configurations, the open trench and the coupled-wave barrier exhibited similar isolation performance and outperformed the sheetpile. In cases the sheetpile has already been installed, the implementation of an open trench in front of the sheetpile may noticeably improve the screening effectiveness.

Quantifying and managing uncertainty in operational modal analysis

Abstract Operational modal analysis aims at identifying the modal properties (natural frequency, damping, etc.) of a structure using only the (output) vibration response measured under ambient conditions. Highly economical and feasible, it is becoming a common practice in full-scale vibration testing. In the absence of (input) loading information, however, the modal properties have significantly higher uncertainty than their counterparts identified from free or forced vibration (known input) tests. Mastering the relationship between identification uncertainty and test configuration is of great interest to both scientists and engineers, e.g., for achievable precision limits and test planning/budgeting. Addressing this challenge beyond the current state-of-the-art that are mostly concerned with identification algorithms, this work obtains closed form analytical expressions for the identification uncertainty (variance) of modal parameters that fundamentally explains the effect of test configuration. Collectively referred as ‘uncertainty laws’, these expressions are asymptotically correct for well-separated modes, small damping and long data; and are applicable under non-asymptotic situations. They provide a scientific basis for planning and standardization of ambient vibration tests, where factors such as channel noise, sensor number and location can be quantitatively accounted for. The work is reported comprehensively with verification through synthetic and experimental data (laboratory and field), scientific implications and practical guidelines for planning ambient vibration tests.

Effective impulse model for prediction of vibration response of high-frequency steel staircases

Nowadays the use of steel staircases is increasing more and more even in reinforced concrete building structures because of the many advantages associated with dry construction. Typical steel staircases often exhibit high-frequency and relatively low-damping characteristics. In addition, they are subjected to footfall forces whose magnitude and pace may be quite different from those caused by walking on a building floor. However, design guides for such high-frequency steel staircases are quite limited. In this study, the effective impulse model is proposed based on full-scale vibration tests that can be used to predict the vibration response of high-frequency steel staircases. It is shown that the proposed model gives more consistent and more accurate predictions than existing comparable methods over the pace frequency range of 1.4Hz to 4.5Hz expected in staircases.

Study on the Derailment Mechanism of Railway Vehicle by Earthquake Ground Motion with a Full Scale Bogie on Roller Rigs

The derailment mechanism for when earthquakes occur has been verified in vibration bench tests and simulations in the past. However, in the past full-scale vibration bench tests including ours, the wheels did not rotate. The aims of this study are to verify the derailment mechanism in case that the railway vehicle running at a high speed is vibrated by a large lateral displacement of track during earthquakes, and to reconfirm the past other verifications. In order to realize this aim, we conducted the full-scale vibration tests with an actual series N700 bogie on roller rigs by use of the rolling stock field test simulator. This apparatus enables to simulate running tests with one or half rolling stock on roller rigs which can experience a considerable degree of horizontal displacement. As a result of this vibration test with an actual bogie on roller rigs, we were able to confirm the influence of wheel rotation on the wheel lift motion, the anti-derailing guard rail acting on a rotating wheel, and so on.

Full-scale dynamic testing and modal identification of a coupled floor slab system

This paper presents work on full-scale vibration testing of the 2nd and 3rd floor slabs of the Tin Shui Wai Indoor Recreation Center. The slabs are supported by one-way long span steel trusses, which are connected by diagonal members and vertical columns to form a mega-truss. On the 2nd floor are a large multi-function room and children play area, while the 3rd floor hosts two basketball courts. Based on their expected usage, significant cultural vibrations with possible rhythmic activities can be expected. To determine the dynamic characteristics of the constructed slab system, ambient and forced vibration tests were performed. Thirty-five setups were carried out in the ambient test to determine the mode shapes using six triaxial accelerometers. A recently developed Fast Bayesian FFT Method is used to identify the modal properties using the ambient data in individual setups. The mode shapes from the individual setups are assembled by a least square fitting procedure. Forced vibration tests were performed by loading the slabs at resonance with a long-stroke electromagnetic shaker, resulting in vibration amplitudes in the order of a few milli-g. A steady-state frequency sweep was carried out and the modal properties were identified by least square fitting of the measured steady-state amplitude spectra with a linear dynamic model. The dynamic properties identified from the ambient and forced vibration tests, as well as their posterior uncertainty and setup-to-setup variability, will be compared and discussed. The field tests provide an opportunity to apply the Fast Bayesian FFT Method in a practical context.

Field Measurement and Modal Identification of a Coupled Floor Slab System

This paper presents work on full-scale vibration tests of the second and third floor slabs of the Tin Shui Wai Indoor Recreation Centre. The concrete slabs are supported by one-way long span steel trusses and are connected by diagonal members and vertical columns to form a mega-truss. To determmine the actual dynamic characteristics of the constructed slab system, ambient and forced vibration tests were performed. Thirty five setups were performed in the ambient vibration test to determine the mode shapes with a high spatial resolution. A recently developed Fast Bayesian FFT Method was used to identiify the modal properties using the ambient data, where the mode sshapes from individual setups were assembled by least square fitting. Forced vibration tests were performed by exciting the slabs with a long-stroke electromagnetic shaker, resulting in vibration amplitudes of the order of a few milli-g. A frequency sweep was carried out in the forced vibration tests and the modal properties were identified by least square fitting of steady-state amplitude spectra. The dynamic properties identified from the ambieent and forced vibration tests will be compared and discussed.

3階建木質接着パネル構法住宅の実大振動実験 : 木質接着パネル構法住宅の実大振動実験 その1

3階建木質接着パネル構法住宅の実大振動実験 : 木質接着パネル構法住宅の実大振動実験 その1

On the dynamic instability of components in complex structurest

The case where one structural member of a larger complex structure experiences a dynamic instability is addressed. An averaged integral representation of the overall structure is chosen, except for the structural member of interest which is modelled precisely by means of the conventional methods of vibration theory. Material damping and the energy dissipation between components are taken into account by means of a distributed elastic-plastic rheological model. Particular attention is paid to keeping the intrinsic nonlinear properties of the energy dissipation. Structural members prove to act as dynamic absorbers with respect to the primary structure. The phenomenon of vibration saturation in complex structures is revealed and discussed. Full-scale vibration testing of a complex structure driven by an electromagnetic shaker is considered as an application of the concept. The moving coil of an electromagnetic shaker is shown to be dynamically unstable if an experiment is not properly designed. The influence of the large vibrating structure on the stability chart of the shaker turns out to be considerable and it changes the shaker’s stability chart drastically.

Forced Vibration of Full-Scale Wall-Backfill System

A full-scale vibration test is conducted to measure the low-amplitude dynamic characteristics of a reinforced concrete cantilever wall-backfill system. Measurements during a frequency sweep are recorded along the wall length. From these measurements, resonant frequencies are identified, along with the corresponding response configurations that depict variation in motion along the wall length. In general, the wall and adjacent backfill zone are observed to move together in-phase. Farther away from the wall, out-of-phase wall-backfill motions are measured at higher resonant frequencies. Finally, retaining systems of uneven height, such as wing walls, are shown clearly to exhibit three-dimensional (3D) seismic response characteristics.

A concept for earthquake protection of the Bucharest tandem accelerator

A concept for an earthquake protection of a tandem accelerator has been developed starting from a better understanding of the earthquake effects upon an FN column structure as a result of dynamic interaction between the ground, building and accelerator. The characteristics of earthquakes in Bucharest as well as the preliminary full-scale vibration tests are described. The main requirements for an efficient earthquake protection system are derived. These requirements are best met by a protection system that performs the vibration isolation of the accelerator tank by supporting it on spring and damper units. By means of specially designed devices (“mechanical fuses”), these units are blocked under normal operation conditions to ensure the alignment of the accelerator and are released in case of an earthquake whose acceleration exceeds a certain limit. Such a vibration isolation system might be useful for other scientific or industrial equipment too.

組積弾性体系の地震応答解析法

During the 1978 Miyagi-ken-oki earthquake in Japan, many stacked crates collapsed in warehouses and factories, not only causing economic losses but also creating menace to the safety of workers. Full scale vibration tests were carried out to study the dynamic properties of the stack. Vibration modes at small amplitude were similar to that of the uniform flexural cantilever beam. At larger amplitude, the vibration period became longer, and the rocking motion was observed at the bottom of the stack. An analytical method was developed to reduce the dynamic properties of stacked elastic body into a single-degree-of-freedom model by means of Galerkin's method. The model considers the elastic vibration before uplifting, the conservation of angular momentum at the instance of uplifting and landing, and the decrease of base shear after uplifting.

“Magnification Factors in the Higher Modes of Ship Vibrations”

An analysis is made of the dynamic magnification factors in the higher modes of ship vibrations, using the experimental data obtained from full-scale vibration tests. From these data, it is derived that the values of dynamic magnifiers have the general tendencies to decrease evidently at the natural frequencies over 300 c. p. m. in the case of vertical vibration and over 350 c. p. m. in the case of horizontal vibration. In order to investigate these phenomena, the author has carried out some theoretical calculation, and it becomes clear that the local vibrations of ship have a great influence upon the magnitudes of dynamic magnifiers. And using these actual ships' data, the author derives some empirical formula for estimating the magnification factors in the higher modes of ship vibrations.