Recorded Time Histories Research Articles

A Multi-Objective Ground Motion Selection Approach Matching the Acceleration and Displacement Response Spectra

For seismic resilience-based design (RBD), a selection of recorded time histories for dynamic structural analysis is usually required. In order to make individual structures and communities regain their target functions as promptly as possible, uncertainty of the structural response estimates is in great need of reduction. The ground motion (GM) selection based on a single target response spectrum, such as acceleration or displacement response spectrum, would bias structural response estimates leading significant uncertainty, even though response spectrum variance is taken into account. In addition, resilience of an individual structure is not governed by its own performance, but depends severely on the performance of other systems in the same community. Thus, evaluation of resilience of a community using records matching target spectrum at whole periods would be reasonable because the fundamental periods of systems in the community may be varied. This paper presents a GM selection approach based on a probabilistic framework to find an optimal set of records to match multiple target spectra, including acceleration and displacement response spectra. Two major steps are included in that framework. Generation of multiple sub-spectra from target displacement response spectrum for selecting sets of GMs was proposed as the first step. Likewise, the process as genetic algorithm (GA), evolvement of individuals previously generated, is the second step, rather than using crossover and mutation techniques. A novel technique improving the match between acceleration response spectra of samples and targets is proposed as the second evolvement step. It is proved computationally efficient for the proposed algorithm by comparing with two developed GM selection algorithms. Finally, the proposed algorithm is applied to select GM records according to seismic codes for analysis of four archetype reinforced concrete (RC) frames aiming to evaluate the influence of GM selection considering two design response spectra on structural responses. The implications of design response spectra especially the displacement response spectrum and GM selection algorithm are summarized.

Characterization of translating tornado-induced pressures and responses of a low-rise building frame based on measurement data

This study presents an analysis and characterization of dynamic wind pressures and internal forces of a low-rise building frame using measurement data obtained from a tornado simulator. The deterministic time-varying mean pressure component is extracted from the time history record using discrete wavelet transformation (DWT) approach. A continuous wavelet transformation (CWT) based approach is employed for determining the evolutionary power spectral density (EPSD) functions and time-varying standard deviation (STD) as well as co-variance of dynamic pressures. The results showed that the characteristics of dynamic pressures are strongly affected by the location of tornado, and are very different from those under straight-line wind. The pressure drop caused by tornado vortex plays a key role in defining the pressure characteristics. The building frame responses are also calculated from the statistics of pressures. The equivalent static wind loads (ESWLs) causing peak responses are defined by using the gust response factor approach. The effect of translation speed of tornado vortex is also investigated. The translating tornado vortex leads to a delay of occurrence of maximum time-varying mean and STD, and reduction in maximum STD thus peak response. It also makes the energy distribution of pressure fluctuations shifted to higher frequencies with a broader power spectrum. Finally, it is shown that the tornado-induced responses are significantly higher than those from ASCE 7-10.

Test my product using sine or random?

As you know, in the vibration world, there are quite a few test “types” to which you can expose your product. The major choices are Sine, Random, Classical Shock, Transient Shock, Field Recorded Time History, Sine-on-Random, Random-on-Random and Sine-and- Random-on-Random. Frequently, our customers will request advice on which of these types of test to run on their product, and in particular, how to choose between the two most common test types: sine or random. Their desire is to know which test, sine or random, is best to most quickly pinpoint flaws in their product. If they can only run one test, either sine or random, which should it be? Recently, I received an even more specific request from a customer. This customer (Don) presented both a sine test and a random test and wanted to know, given both a sine test and a random test, how he could determine which is the most severe? Let’s take a look at the two tests and decide how to answer to his question. Here is Don’s question: How would the following specifications compare with regard to amplitude/severity?

Determination of the bottom deformation from space- and time-resolved water wave measurements

In this paper we study both theoretically and experimentally the inverse problem of indirectly measuring the shape of a localized bottom deformation with a non-instantaneous time evolution, from either an instantaneous global state (space-based inversion) or a local time-history record (time-based inversion) of the free-surface evolution. Firstly, the mathematical inversion problem is explicitly defined and uniqueness of its solution is established. We then show that this problem is ill-posed in the sense of Hadamard, rendering its solution unstable. In order to overcome this difficulty, we introduce a regularization scheme as well as a strategy for choosing the optimal value of the associated regularization parameter. We then conduct a series of laboratory experiments in which an axisymmetric three-dimensional bottom deformation of controlled shape and time evolution is imposed on a layer of water of constant depth, initially at rest. The detailed evolution of the air–liquid interface is measured by means of a free-surface profilometry technique providing space- and time-resolved data. Based on these experimental data and employing our regularization scheme, we are able to show that it is indeed possible to reconstruct the seabed profile responsible for the linear free-surface dynamics either by space- or time-based inversions. Furthermore, we discuss the different relative advantages of each type of reconstruction, their associated errors and the limitations of the inverse determination.

Seismic response of reduced scale stone masonry building

The results of shaking table tests of a one-third stone masonry building model have been presented in this paper. The model was subjected to four levels of acceleration–time history record of the 1940 El Centro earthquake. These levels include 75% (R75), 100% (R100), 125% (R125) and 150% (R150). The data relating to acceleration and displacement were recorded and analysed. The fundamental mode of vibration of the structure was observed at all the levels of ground acceleration that were employed. The in-plane walls at the first storey were severely damaged as the structure was subjected to the increasing levels of peak ground acceleration. The maximum structure response to the ground vibration was observed at the R100 level of acceleration–time history. The fundamental frequency of the model decreased from 9/s for the virgin structure to 1/s after the R150 test run, whereas the damping ratio increased from 4·88 to 29·77%. The idealised resistance curve of the tested model indicated a structure ductility of 2·18.

Wavelet Packet Characterization of Scenario Earthquake Ground Motions

With increased emphasis on performance-based seismic design, the need for appropriate ground motion time histories for use in nonlinear dynamic analyses is felt accutely. However, it is generally not possible to get a suitable recorded time history consistent with the estimated hazard at a specific site. The ground motion prediction models are therefore derived/developed from a statistical analysis of recorded ground motion for a variety of source and site conditions to address this need. Most often, the ground motion prediction models are developed to model the response spectrum amplitudes at a set of natural periods and the ground motion time history, if required, is then generated to be consistent with this predicted response spectrum. These simulated time histories often lack in modeling the wave arrivals and temporal variation in the distribution of energy with respect to frequency. In this paper, we present a wavelet-based ground motion prediction model for directly generating ground motion time history that is consistent with the postulated scenario earthquake at a site.

A Data-based Probabilistic Approach for the Generation of Spectra-Compatible Time-History Records

ABSTRACTA data-based procedure is presented to develop spectra-compatible time-history records that are based on the dominant probabilistic features of an ensemble of records corresponding to the non-stationary stochastic phenomena of interest (e.g., earthquakes, wind loads, etc). The method requires a statistically significant collection of time-history records that are used to construct the associated covariance kernel of the random process. Subsequently, orthogonal decomposition approaches are used to determine the dominant eigenvectors of the covariance matrix, and these vectors are then linearly combined, with an adjustable amplitude-scale and phase-shift, to determine, via a nonlinear optimization scheme (employing a combination of stochastic and deterministic approaches), a time-history record that matches the target spectrum within a specified error bound. The utility of this approach is demonstrated with several collections of earthquake records from different regions of the world (Japan, Los Angeles, and San Francisco) that are then used to match various spectra widely used in seismic design applications. Issues that impact the selection of the bases vectors to construct the optimum spectra-matching record are discussed, and guidelines are provided for successful implementation of the proposed methodology.

Seismic response analysis in the southern part of the historic centre of the City of L’Aquila (Italy)

This paper deals in the 2011 extensive site investigation by means of boreholes up to a depth of 80m, Down-Hole (D-H) tests, Seismic Dilatometer Marchetti Tests (SDMT), Multichannel Analysis of Surface Waves (MASW) tests in the area of via XX Settembre of the city centre of L’Aquila (Italy), to obtain a detailed geotechnical model. Results of site investigations showed a marked variability of shear wave velocity Vs profiles, especially in the upper 5–10m, where different soil types are commonly encountered, all characterised by low values of Vs.In this paper the main features of the April 6, 2009 L’Aquila Earthquake (ML=5.8; MW=6.3) are also discussed. The earthquake caused 308 casualties and heavy damage in the city of L’Aquila and in the surroundings villages. Some accelerometric stations were located across the Aterno River Valley, while only one station (namely AQK) was located in the city centre of L’Aquila. The peak acceleration values ranged from 0.35g recorded in the city centre to 0.65g recorded in the middle Aterno valley. The recorded time histories were characterised by short durations and high peak accelerations both in the horizontal and in the vertical directions.The area of via XX Settembre (southern part of the historic centre of the city of L’Aquila) was severely damaged by the earthquake. This area, located at a very short distance from the city centre, includes also some reinforced concrete frame buildings, mostly 5–7 storey high, built between 1950 and 1965. Old masonry buildings and some of these r.c. buildings collapsed or suffered severe damage due to the main shock, causing several tens of victims. The peculiar subsoil conditions locally detected down to about 40m depths in this area include fine-grained soils interposed within, or placed above, “Brecce dell’Aquila” (typical of L’Aquila) and man-made fills. Low and variable shear wave velocity VS values in the upper portion of the subsoil have locally originated major amplification of the ground motion during the main shock.Therefore the paper deals also in specific one-dimensional numerical seismic response analyses performed. Significant amplification effects related to local subsoil conditions, bigger than the amplification factors given by the Italian Building Code NTC 2008, have been discovered by the seismic response analyses carried out at the site. The results of soil response analyses were compared with the occurred damage in the area.

Characterization of the Dynamic Behavior of Shallow Foundations with Full-Scale Dynamic Tests

AbstractThis work provides a detailed description of the full-scale experimental tests performed on the dynamic behavior of a shallow foundation under intermediate strains. A wind tower supported by the foundation was subjected to a snap-off test, i.e., it was first pulled with a cable and then suddenly released, thus inducing free oscillations of nonnegligible amplitude in the whole system. The motion induced was measured with a digital camera, seismometers, and accelerometers attached to the surrounding ground surface and to the wind tower. An innovative interpretation technique based on optimizing a few meaningful parameters obtained from the recorded time histories was required by the heterogeneity of the data collected and the accuracy needed to deduce the behavior of the foundation plinth. The analyses showed that the rotational stiffness of the foundation plinth was approximately 10 times greater than that of the base joint, which in turn was approximately one order of magnitude greater than that o...

Design Ground Motion Library: An Interactive Tool for Selecting Earthquake Ground Motions

The Design Ground Motion Library (DGML) is an interactive tool for selecting earthquake ground motion time histories based on contemporary knowledge and engineering practice. It was created from a ground motion database that consists of 3,182 records from shallow crustal earthquakes in active tectonic regions rotated to fault-normal and fault-parallel directions. The DGML enables users to construct design response spectra based on Next-Generation Attenuation (NGA) relationships, including conditional mean spectra, code spectra, and user-specified spectra. It has the broad capability of searching for time history record sets in the database on the basis of the similarity of a record's response spectral shape to a design response spectrum over a user-defined period range. Selection criteria considering other ground motion characteristics and user needs are also provided. The DGML has been adapted for online application by the Pacific Earthquake Engineering Research Center (PEER) and incorporated as a beta version on the PEER database website.

Shaking Table Test of the Taiwanese Traditional Dieh-Dou Timber Frame

ABSTRACTThis article attempts to explore the dynamic behavior of traditional Dieh-Dou timber structure under different combinations of structural forms and vertical loads. Using time-history record (TCU 084) from the Chi-Chi earthquake, two semi full-scale specimens (Symmetric and Asymmetric) were tested. Results showed that the Symmetric specimen tends to be damaged more easily and faster than the Asymmetric one. Damage pattern generally begins from the bottom Dou members and subsequently spreading upwards to the upper Dou, horizontal Gong members, and adjoining Shu members. Friction force between the contact surfaces is crucial towards the maintenance of overall structure. Increase vertical loadings have significant effect on the natural frequencies and global stiffness of the structure. Using the Single-Degree-Of-Freedom (SDOF) system, the derived stiffness is generally in good agreement with the dynamic results of both forms. This study suggests that the effects of increasing vertical loadings should be taken into consideration for future evaluation.

Gear Diagnostics – Fault Type Characteristics


 
 
 To date, the majority of existing Condition Indicators for gears are based on various statistical moments of a recorded time history. A supplementary analysis proposed in this study, shall suggest an approach that may, in the future, enable the identification of faulty gearwheel and possibly fault type in the system. In this work, a combined analytical and empiric approach is applied. This approach is based on the assumption that reliable dynamic models can be utilized to predict the effects of faults on vibrational patterns. Dynamic model generated signatures are used to verify experimental findings. Moreover, discrepancies between simulated and actual results, combined with understanding of the assumptions and omissions of the model, are helpful in understanding and explaining the experimental results.A spur gear transmission setup was used for experiments, along with an electric AC motor and a friction belt loading device. The experimental runs were conducted at varying speed settings. Two types of faults, a tooth face fault and a tooth root fault, were seeded in the experimental transmission and into the model. The effect on extracted signal features is examined.
 The purpose of this study is to evaluate fault detection capabilities of proposed diagnostic tools at the presence of two seeded faults of varying severity, verified by a dynamic model. Observed differences between examined fault types and their manifestation will be discussed. A basis for future work on prognostics capabilities is laid by a varying degree of tooth root fault.
 
 

Structural Seismic Response Mitigation using Optimized Vibro-Impact Nonlinear Energy Sinks

A nonlinear targeted energy transfer mechanism called Vibro-Impact Nonlinear Energy Sink (VI NES) is studied in the present work for seismic mitigation of building frames. In order to best tune VI NES parameters including clearance and stiffness ratio, the problem is formulated via an optimization framework. To form the objective function and trace the structural behavior, several seismic performance indices developed in previous works are employed. Carrying out nonlinear dynamic time history analyses on a number of low and medium-rise steel moment frames with an attached VI NES and performing Fourier analyses on the obtained structural responses, reveal a short reaction time and broadband energy dissipation in the passively controlled structure through the attached VI NES. VI NES parameters are also determined via the optimization process under the scaled earthquake time history record that has the closest spectrum to the target spectrum. The seismic performance indices are evaluated to test the trained (optimized) case under other earthquake records in the set and yield appropriate results.

An Efficient Algorithm to Identify Strong-Velocity Pulses in Multicomponent Ground Motions

Ground motions with strong velocity pulses are of special concern for structural engineers. We describe an efficient and quantitative method to identify such ground motions. Previous algorithms to classify these pulse-like ground motions con- sidered the ground motion in a single orientation, which made classifying pulses in arbitrary orientations difficult. We propose an algorithm that can identify pulses at arbitrary orientations in multicomponent ground motions, with little extra computa- tional cost relative to a single-orientation calculation. We use continuous wavelet transforms of two orthogonal components of the ground motion to identify the ori- entations most likely to contain a pulse. The wavelet transform results are then used to extract pulses from the selected orientations, and a new classification criterion based on support vector machines is proposed. Because we are mostly interested in forward directivity pulses, which are found early in the time history, a criterion to reject pulses arriving late in the time history is also proposed. The procedure was used to classify ground motions in the Next Generation Attenuation-West2 database (Ancheta et al., 2013). The list of pulse-like ground motions was then manually filtered using source- to-site geometry and site conditions to find the pulses most likely caused by directivity effects. Lists of both pulse-like ground motions and directivity ground motions are provided, along with the periods of the pulses and the orientations in which the pulses were strongest. Using the classification results, new models to predict the probability of a pulse and pulse period for a given future earthquake scenario are developed. Online Material: Table of all the pulse-like ground motions identified in the Next Generation Attenuation-West2 database, and HTML files of source-to-site geometry, the recorded time history, extracted pulse, and other directivity parameters for each identified pulse.

Investigation of Tacking Strategies Using an America's Cup 45 Catamaran Simulator

The recent America's Cup has demonstrated the extreme performance capability of the AC45 and AC72 catamarans. The high cost and risk of catastrophic failure has imposed restrictions on the availability of these boats for training. As a consequence the use of simulators to allow shore-based training becomes an attractive option. The aim of this study is to use a recently developed AC45 tacking simulator to investigate the optimum tack sequence by conducting a parametric study of user control inputs based on previously recorded time histories. The study will provide a better understanding of the influence of the input parameters on the tack and allow improved shore-based training programmes to be developed.

Inverse Analysis of Pavement Structural Properties Based on Dynamic Finite Element Modeling and Genetic Algorithm

With the movement towards the implementation of mechanistic-empirical pavement design guide (MEPDG), an accurate determination of pavement layer moduli is vital for predicting pavement critical mechanistic responses. A backcalculation procedure is commonly used to estimate the pavement layer moduli based on the non-destructive falling weight deflectometer (FWD) tests. Backcalculation of flexible pavement layer properties is an inverse problem with known input and output signals based upon which unknown parameters of the pavement system are evaluated. In this study, an inverse analysis procedure that combines the finite element analysis and a population-based optimization technique, Genetic Algorithm (GA) has been developed to determine the pavement layer structural properties. A lightweight deflectometer (LWD) was used to infer the moduli of instrumented three-layer scaled flexible pavement models. While the common practice in backcalculating pavement layer properties still assumes a static FWD load and uses only peak values of the load and deflections, dynamic analysis was conducted to simulate the impulse LWD load. The recorded time histories of the LWD load were used as the known inputs into the pavement system while the measured time-histories of surface central deflections and subgrade deflections measured with a linear variable differential transformers (LVDT) were considered as the outputs. As a result, consistent pavement layer moduli can be obtained through this inverse analysis procedure.

Impact Pressure on a Flat Wall by Breaking Water Mass

Impact pressures due to breaking wave sometimes caused serious damages on a ship or marine structures. Impact pressure exerted on the face of a flat plate by a breaking mass was studied experimentally and analytically. Experiments have been carried out with a free-falling water mass apparatus. Recorded time history of impact pressures can be categorized into two typical profiles. One is an impulsive peak with a damped oscillation and the other is without the oscillation. The damped oscillation can be explained by a well-known theory with a trapped air pocket between the breaking mass and the plate. And our analytical model with a curved water surface reveals that a change in momentum due to added mass on the plate yields impulsive force.

S191022 回収機カプセル模型着水時の動的応答計測([S191-02]大気突入・減速技術(2))

Japan Aerospace Exploration Agency has a plan to develop the HTV-R which is an extended version of the HTV. The HTY-R will be a spacecraft for developing a re-entry capsule similar to the Apollo spacecraft. The recovery on the sea surface is the promising methods to develop a Japanese capsule, therefore the shock mitigation at splashdown is one of the key technologies. In the present study, preliminary splashdown tests using a 6.8 percent scale model of the re-entry capsule were performed in the required three kinds of splashdown velocities and four kinds of initial attitude angles of the model. A measuring system of acceleration was constructed, which recorded time histories of acceleration and sent the data to PC wirelessly and measured its splashdown behaviors using five accelerometers. Experimental data obtained from five accelerometers are evaluated based on water impact theory that is considered from virtual mass and conservation of momentum. It was made clear that the maximum acceleration at splashdown was obviously mitigated in the case of initial attitude angle 30 degree compared to other initial attitude angles.

On the monitoring of historic Anime Sante church damaged by earthquake in L'Aquila

The paper shows the activity of a 2-year static and dynamic monitoring activity to check the structural response and the actual level of damage of a historic church hit by earthquake in L'Aquila (Italy) in 2009. Structural health monitoring was carried out with accelerometers and transducers that recorded time histories of the main earthquake-induced ground motions and ambient vibrations. The paper focuses particularly on residual performance and assessment of the ancient church after six earthquake response data set—because of the seismic swarm—via a modal identification of output-only systems by using frequency domain decomposition. In this way, fundamental frequency, mode shapes, damping ratios and displacements can be estimated without knowing the input that has excited the system. The dynamic monitoring provides also a way to check possible drops of tension in the cables and relaxation in the FRP belts used for safety. Efficiency and reliability of modal identification of basilica-type churches, via the dynamic response of macro-elements only in comparison with the whole analysis, are finally proposed. Copyright © 2012 John Wiley & Sons, Ltd.

Enrichment of seismic ground motion databases using Karhunen–Loève expansion

SUMMARYBest estimate seismic analysis are generally based on time‐domain simulations of structural responses. The seismic load is then modeled by a stochastic process representing ground motion. For this purpose, the analyst can use recorded accelerograms or work with synthetically generated ones. The number of ground motion time‐histories available for a given scenario and site condition is limited and generally not sufficient for carrying out more advanced probabilistic structural response analysis. It is then necessary to have at our disposal methods that allow for generating synthetic accelerograms that realistically characterize earthquake ground motions. However, most of the methods proposed in literature for generating synthetic accelerograms do not accurately reproduce the natural variability of ground motion parameters (such as PGA, cumulative absolute velocity, and Arias intensity) observed for recorded time histories. In this paper, we introduce a new method for generating synthetic ground motion, based on Karhunen‐Loève decomposition and a non‐Gaussian stochastic model. The proposed method enables the structural analyst to simulate ground motion time histories featuring the properties mentioned above. To demonstrate its capability, we study the influence of the simulation method on different ground motion parameters and on soil response spectra. We finally compute fragility curves to illustrate the practical application of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.