Table Experiments Research Articles

A comparative study of hybrid simulation and dynamical substructuring system schemes for shake table tests

In shaking table experiments, the dynamics of the shake table is strongly affected by a specimen to be tested, particularly when the specimen is very heavy. This is also the case when substructuring experiments are implemented by the shaking tables. This study numerically examines two substructuring schemes applied in shaking table experiments. Hybrid simulation scheme, which is commonly used in substructuring experiments, directly uses the output of the numerical substructure as the input to the physical substructure. Dynamical substructuring system (DSS) scheme, which requires more complicated control design, determines the control input to minimize control error obtained by outputs of numerical and physical substructures. This study has found that, in shaking experiments, the stability of the hybrid simulation scheme is very sensitive to a pure time delay. It is also found that DSS scheme can provide much higher stability margin against the pure time delay than the hybrid simulation scheme. The effort to rather complicated controller design of DSS scheme will be rewarded at actual control practices.

Fractal-like overturning maps for stacked rocking blocks with numerical and experimental validation

A novel, compact mathematical formulation is presented to describe the dynamic rocking response of single and double block systems subjected to gravity and/or ground excitation. The derivation of the closed-form solutions of impacts and motion is based on the conservation of angular momentum and the Euler-Lagrange equation, respectively, and combines all the different cases of possible block relative rotating and impact modes (16 in total) into a single set of equations without the need of transient expressions. The derived equations that describe the impact modes are the equivalent to the expression derived by Housner and depend on the angular velocity of the blocks before impact. The analytical model is integrated numerically via an ad hoc algorithm and its reliability & accuracy are verified after various self-consistency tests and comparisons with the literature. In addition, several shaking table experiments were conducted in EQUALS laboratory in Bristol, set-up constructed to test free and forced rocking motion of single and double block configurations. The error margins of the measurements are determined, and the extracted data are in good agreement with the numerical results for most examined cases. The ideal Housner restitution coefficient of single block impact to a rigid base is adjusted to match experimental conditions, and it is found to be correlated with the block aspect ratio. The forced rocking of a two-block system is shown to exhibit numerous different response patterns depending on the excitation conditions. The integrated model is finally applied to produce normalised overturning maps for double block systems, subjected to single-pulse sine inputs, which uncover the existence of a fractal-type behaviour. This previously unsuspected trait of multi-block systems is reminiscent of the chaotic behaviour exhibited by a classical double pendulum and suggests that the risk of overturning can only be evaluated on a probabilistic sense.

Frequency and intensity dependent dynamic responses of soil-steel pipe sheet pile (SPSP) foundation-superstructure system

Frequency and intensity dependent dynamic response behavior of soil-steel pipe sheet pile (SPSP) foundation and superstructure supported on it is studied in this work considering the soil-structure interactions (SSI) effect through experimental investigation by utilizing a physical scaled model of soil-SPSP foundation-superstructure (S-SPSP-S) system. The vertical shear resistance of SPSP foundation joint is assessed experimentally by using an element model of SPSP joint and the result satisfies the requirement laid in design code. The components of sub-structuring solution technique for dynamic response computation namely-the inertial interaction effect and the kinematic interaction effect are estimated through SPSP foundation head loading test and shake table experiment under 1-g conditions, respectively. Frequency and intensity dependent SPSP foundation head impedance functions (IFs) and effective foundation input motion (EFIM) are estimated from these experiments for inertial interaction and kinematic interaction, respectively. The total dynamic response of S-SPSP-S system is computed using the sub-structuring technique through superposition of the experimentally measured IFs and EFIM. The superimposed dynamic response is further compared with the experimental total dynamic response estimated from shaking table experiment with the model S-SPSP-S system. The comparison shows certain discrepancies particularly in resonance behavior of SPSP foundation system. The reason for such observed difference is the stiffness variation of SPSP foundation unit due to the nonlinear behavior of SPSP joint resulting from profound influence of superstructure mass. As a whole, the results and discussions presented in this paper will provide the reader a detail insight on the fundamental dynamic response behavior of S-SPSP-S system.

Toxicity of cyanobacterial blooms from the reservoir Valle de Bravo (Mexico): A case study on the rotifer Brachionus calyciflorus

Proliferating cyanobacterial blooms due eutrophication in reservoirs is a major global problem. The production of cyanotoxins often increases with grazing pressure and temperature while the sensitivity of zooplankton to cyanotoxins is directly related to temperature. Here we evaluate the effect of different concentrations of the crude extract of cyanobacteria from Valle de Bravo reservoir during dry (January) and rainy (September) seasons at 20 and 25 °C on the rotifer Brachionus calyciflorus based on acute and chronic toxicity tests. We filtered 20 or 150 l of lake water, depending on the intensity of the bloom, and estimated the density and diversity of the cyanobacteria. The crude extracts, after 5 cycles of freezing, thawing and sonication at 14 MHz, were filtered and the microcystin concentration quantified based on ELISA. The extracts were used to conduct the acute and chronic toxicity tests, all in quadruplicate. Acute toxicity tests were based on 24 h mortality. Chronic toxicity tests (population growth and life table experiments) were conducted at 5 and 10% of the median lethal concentration. The field samples were dominated by Microcystis sp. (January) or Woronichinia naegeliana (September). The microcystin concentration in lake water was 9.57 μg/l and 0.097 μg/l and the median lethal concentration was 5.34 μg microcystin/L and 0.35 μg microcystin/L in January and September, respectively. Survival and reproduction of B. calyciflorus were lower in the presence of the cyanobacteria crude extract, more so at 20° than at 25 °C. Our results highlight the urgency of regular monitoring based on zooplankton assays for reservoirs in tropical and temperate regions, subject to frequent and dominant cyanobacterial blooms, often as a result of climate change.

Elimination of a measurement problem: A robust prediction model for missing eigenvector value to assess earthquake induced out-of-plane failure of infill wall

One of the effective methods to assess local or global behavior of structural system is to perform shake table experiment. The biggest challenge of all experiments, either shake table or others, are missing data during the experiments due to removed instruments. This problem is arose especially during the out-of-plane tests. This problem is named as “Measurement” problem. This paper is focused on detection the measurement problem and solving this problem by using Adaptive-Network Based Neuro Inference System (ANFIS). Definition of the problem is briefly missing out-of-plane eigenvector value during the implementation of a shake table experiments on a full scale one bay one storey reinforced concrete structural system. For this aim, two shake table experiments were performed with reinforced concrete frame (RCF) and infill wall at the National Civil Engineering Laboratory (LNEC) Portugal. The out-of-plane failure of infill wall was assessed under combined bidirectional seismic load. Shake table experiments were conducted on two types of specimens. One of them is Unreinforced Brick Infill Wall (URBIF) composed of single layer 22 cm thick brick. The other is single layer 22 cm thick Infill Wall with Bed Joint Reinforcement solution (IwBJR). Both specimens were made of a single-layer brick infill wall enclosure with the RCF. Bed joint reinforcement term refers horizontal bed joint reinforcement as a strengthening technique. Shake table experiments were performed on each specimen at four stages. After third level of earthquake load, the accelerometers were removed on the wall to prevent damage to them. The removal of these instruments results in missing data. The missing eigenvector values were predicted with a robust Adaptive-Network Based Neuro Inference System (ANFIS) model to present failure mode of infill wall. The estimation quality was tested with R2, Mean Absolute Percentage Error (MAPE), Mean Square Error (MSE) and Root Mean Square Error (RMSE) among with available data. The results of the quality indicator of R2 are 0.999 for URBIF model and 0.997 for IwBJR model, respectively. Moreover, rest of the indicator results are less than %1. The proposed approach is reliable on the base of quality indicator. Moreover, this study can be used for seismic engineering to predict eigenvector values to see local behavior of infill wall and mode shape evolution to determine which mod prone for partial and total collapse of infill wall.

Unseating mechanism of a skew bridge with seat-type abutments and a Simplified Method for estimating its support length requirement

In this paper, the unseating mechanism of a skewed bridge during earthquake shaking is investigated. To begin, an existed unseating mechanism in literature, which was proposed by other researchers, is described. The mechanism hypothesizes that under lateral loading, the obtuse corner of the superstructure of a skew bridge engages the adjacent back wall and the superstructure then rotates about this corner, causing large in-plane displacements at the acute corner at the other end of the span, potentially unseating the edge girder. It is then validated using data from a comprehensive set of shake table experiments recently conducted by the author and other researchers. Whereas the experimental data confirms this mechanism as the primary reason for the rotation, it is not the only reason. Impact of the span against the back wall is followed immediately by rebound away from the wall and the span continues to rotate in the same direction in free vibration about the center of stiffness of the substructure. This additional rotation further increases the superstructure rotation and the in-plane displacement of the acute corner. Based on the existed mechanism, a Simplified Method is then developed to estimate the support length requirements of skew bridges. This method, which is based on response spectrum analysis, can consider the closure of expansion gap. The basic procedures are described for the AASHTO’s design spectrum, and spectrum of an arbitrary ground motion. A closed form solution is achievable for the former spectrum, while iteration is required for the latter spectrum. The results are then compared with the experimental dataset. It is found that the accuracy of the Simplified Method depends on the gap size. That is: it overestimates the maximum displacements normal to the abutment of skew bridges when the gap is small, accurately estimates when the gap is in a typical range, and underestimates when the gap is large. The underestimation is mainly because the Simplified Method neglects the “bounce back” effect of skew bridges. Therefore, the Simplified Method may be used for the preliminary design of bridges with standard gap sizes, but should be modified to include “bounce back” effect when the gap is large.

Causes of mortality at different stages of Cactoblastis cactorum in the native range

Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is native to South America and has been used successfully as a biocontrol agent against invasive species of Opuntia (Cactaceae). After its release in the Caribbean, it entered North America, dispersed to southeastern USA, and may reach Mexico threatening native cacti biodiversity and industry based on Opuntia spp. Identifying mortality factors acting on insect populations is central to develop pest management programs. The objective of this study was to estimate mortality causes of C. cactorum in its native range through life table experiments conducted on the exotic O. ficus-indica (L.) Miller and the native species O. quimilo K. Schum. and O. megapotamica Arechav., to detect vulnerable stages and natural enemies. The main mortality factors were generalist predators and native plant defenses. Apanteles opuntiarum Martinez & Berta (Hymenoptera: Braconidae) was found to be the parasitoid with the highest potential as a biocontrol agent.

Revival of water table experiments in fluid mechanics courses, part I

In a classroom environment, after a comprehensive theoretical discussion of compressible flows, it is beneficial to conduct a visual experiment in which students can observe these flows and some of the features associated with them. Experimental study of compressible fluid dynamics is associated with high equipment costs; therefore, conducting an experiment is not feasible for some colleges. This article describes an experiment implemented at Manhattan College upper division and graduate fluid dynamics courses at a relatively low cost. In the experiment, a water table hydraulic analogy was used. Theoretical considerations of this analogy are explained in this article. An area–velocity relation was used to study the Mach number at the exit of a Laval nozzle. The theory and measurement came within 10% of each other, which is sufficient for a teaching demonstration. This exercise can be conducted in two class sessions: (1) discussing the theoretical considerations and (2) performing the experiment and analyzing data. The overall experience is a good way to help students understand some of the compressible flow features, and further promote their interest in fluid mechanics.

Similitude theory for scaled friction pendulum bearings for shaking table experiments

Scaled models of friction pendulum bearings (FPBs), which require a similitude design based on a set of scaling laws, are typically employed in shaking table experiments to investigate the seismic behavior of the models. In this study, scaling laws for scaled FPBs are developed to determine the physical parameters of their models. Then, an equivalent method for the distribution of scaled FPBs in the model isolation layer is proposed for scaling cases in which fewer FPBs are arranged in the model than in the prototype. In addition to an accurate simulation of the global seismic response of the prototype isolation layer, the proposed equivalent method also aims to simulate the possible worst-case loading conditions of an individual FPB in a prototype. A model of an FPB-isolated space truss on top of four towers was scaled, manufactured and tested on a shaking table. A comparison of the seismic response of the global isolation layer and the individual FPB between the model and the prototype demonstrates the effectiveness of the developed theory.

Demographic responses underlying eco-evolutionary dynamics as revealed with inverse modelling.

Changes in population dynamics due to interacting evolutionary and ecological processes are the direct result of responses in vital rates, that is stage‐specific growth, survival and fecundity. Quantifying through which vital rates population fitness is affected, instead of focusing on population trends only, can give a more mechanistic understanding of eco‐evolutionary dynamics.The aim of this study was to estimate the underlying demographic rates of aphid (Myzus persicae) populations. We analysed unpublished stage‐structure population dynamics data of a field experiment with caged and uncaged populations in which rapid evolutionary dynamics were observed, as well as unpublished results from an individual life table experiment performed in a glasshouse.Using data on changes in population abundance and stage distributions over time, we estimated transition matrices with inverse modelling techniques, in a Bayesian framework. The model used to fit across all experimental treatments included density as well as clone‐specific caging effects. We additionally used individual life table data to inform the model on survival, growth and reproduction.Results suggest that clones varied considerably in vital rates, and imply trade‐offs between reproduction and survival. Responses to densities also varied between clones. Negative density dependence was found in growth and reproduction, and the presence of predators and competitors further decreased these two vital rates, while survival estimates increased. Under uncaged conditions, population growth rates of the evolving populations were increased compared to the expectation based on the pure clones.Our inverse modelling approach revealed how much vital rates contributed to the eco‐evolutionary dynamics. The decomposition analysis showed that variation in population growth rates in the evolving populations was to a large extent shaped by plant size. Yet, it also revealed an impact of evolutionary changes in clonal composition. Finally, we discuss that inverse modelling is a complex problem, as multiple combinations of individual rates can result in the same dynamics. We discuss assumptions and limitations, as well as opportunities, of this approach.

Reproductive isolation, morphological and ecological differentiation among cryptic species of Euchlanis dilatata, with the description of four new species

Morphological approaches may not provide sufficient resolution for species delineation. Thus, we used an integrated approach that included molecular and ecological characters as well as morphological features to gain a better estimate of species diversity and to improve our understanding of the speciation process within rotifers. Previously, seven putative cryptic species were found within Euchlanis dilatata complex based on a nuclear marker. Here, we investigated reproductive isolation, variation in trophi morphology, and life history characteristics among representatives of some of these species. Mating success between each cryptic species was 0–1.1%; lower than that of positive controls (intra-clonal: 15.6–43.9%). SEM trophi images representing individuals from all seven lineages were used for morphometric analyses. Using Discriminant Analysis, 64% of individuals were correctly assigned to cryptic species. Five clonal lineages, each representing a putative species, were used in life table experiments with varying temperature and conductivity. Age-specific fecundity increased under high temperature and life expectancy decreased under high temperature and high conductivity. There was variation among cryptic species in some life table characteristics, such as life expectancy and generation time. Applying an integrative taxonomy approach, we examined the boundaries between E. dilatata cryptic species and described four of them as new species.

Experimental study of the effect of a flexible base on the seismic response of a liquid storage tank

Previous studies have demonstrated that strong earthquakes can cause severe damage to storage tanks. In many countries tanks are built near the coast on soft soils. Because of the difference in stiffness between the tank (rigid) and the soil (flexible), the soft soil causes an elongation in the period of the impulsive mode of the soil-foundation-tank system and, therefore, this flexible base can have an important effect on the seismic response. Numerical studies by other researchers have shown the influence of a flexible base on the seismic response of storage tanks. However, experimental investigation on the effects of a flexible base using sand box on the key design parameter, i.e. stress developed in the tank shell, has not been reported. In this research shake table experiments were performed. Sand in a box is used to simulate the flexible base. Actual earthquake records scaled to the New Zealand design spectrum for Wellington City are used. The results showed that in comparison with the rigid base case (model placed directly on the shake table) the axial compressive stresses decreased. The experimental results are corroborated by a numerical model.

An experimental investigation on the dynamics of liquid sloshing in a rectangular tank and its interaction with an internal vertical pole

In the present study we perform shake table experiments to study the fluid structure interaction effects between the sloshing liquid and the internal structure. A partially filled storage tank is systematically subjected to (i) horizontal (ii) vertical and (iii) seismic excitations. To start with, forced horizontal excitations are imposed by varying the amplitude of excitation ranging from 0.001 L to 0.0075 L, where, L is the tank length. As the amplitude of excitation is increased, sub-harmonic wave features were observed at the wave crests, which indicate the presence of higher slosh modes. The resulting resonant free surface oscillations are validated against available theoretical and computational studies. Furthermore, the tank was subjected to vertical harmonic excitations at nth slosh frequency (ωn), where, n = 1, 2, 3 and 4 covers first four sloshing modes. The excitation frequency (Ωn = ωn∕ωv) of 0.5 and the corresponding forcing amplitudes (κv) are chosen such that, the combinations were with in the unstable range of Matheiu's instability diagram. For higher modes of vertical excitation, the free surface oscillations were found to be better damped. A detailed study of flow visuals, free surface fluctuations, dynamic pressure data, power spectral densities, structural responses etc reveal the nature of coupling with the container wall and the circular cylinder. The shake table is further programmed to simulate the well known El Centro earthquake excitation, where the storage tank is imposed with horizontal as well as combined horizontal and vertical components of excitation (at 50% of actual amplitude) to investigate the fluid structure interaction effects. When the partially filled storage tank is subjected to seismic excitation, spiky jet like features were observed over the free surface.

Theoretical studies of the geophone coupling influence in the bare carbonate rock area

Extremely abundant oil and gas resources in the sedimentary basins of marine carbonate which are of vast areas exist in South China. However, it is very difficult to make a wonderful geophone coupling with the outcrop of hard limestone. And then the qualities of the seismic data are reduced. Now, geophone coupling test is of great blindness due to lack of appropriate theoretical guidance. In this paper, in order to understand fully the transmission mechanism of the geophone-limestone coupling system, considering that the coupling mediums such as gesso, clay and so on are used in field seismic data acquisition, I bring forward the theory of geophonelimestone 3-DOF (degree of freedom) coupling system based on vibration dynamic concept. The geophonelimestone coupling system responses are computed when the parameters of coupling medium, geophone spikes and damping are changed. And we find that the geophonelimestone coupling system is a resonance system which has three resonance frequencies. The results show that the resonance frequency can be increased through increasing the elastic modulus of the coupling medium, decreasing the area of the underside and the height of the coupling medium, using spikes with lower material density and reducing the height of the spike. The results also show that the impact of the narrow frequency bands ?band pass filtering? can be decreased by increasing the damping of the coupling system properly. Finally, we preliminary validate the theoretical results of the geophone-limestone 3-DOF coupling system using shake table experiments.

Verification of performance criteria using shake table testing for the vulnerability assessment of reinforced concrete buildings

SummaryShake table experiments are conducted to support the selection of performance criteria and to verify the inelastic modeling approach for developing the fragility functions of reinforced concrete buildings. Two frames representing the lateral force‐resisting system of a preseismic code building are tested under the effect of an earthquake record with increasing severity. Shear failure is detected in columns at a PGA of 1.28g before other failure modes, which was effectively predicted by the fiber‐based numerical model, performance criteria, and shear supply approaches adopted for vulnerability assessment. Five buildings, ranging from 2 to 40 stories, are then assessed under the effect of far‐field and near‐source earthquake records, considering the experimentally verified modeling approach and shear failure prediction models that account for flexural ductility and shear‐axial force interaction. The impact of considering shear response on the vulnerability assessment results is considerable, particularly for the lower‐height wall structures when subjected to the near‐source earthquake scenario. Higher modes dominate the behavior of wall structures, principally under the latter seismic scenario, and shift their response to shear‐controlled. Therefore, seismic scenario‐structure‐based performance criteria are adopted for developing a range of analytically derived, experimentally verified fragility functions for the earthquake loss estimation of buildings with different characteristics.

Numerical and experimental study on scaled soil-structure model for small shaking table tests

The goal of this study is to determine an appropriate geometric scaling coefficient for small-capacity shaking table tests representing the full-scale field conditions rigorously for the soil-structure interaction (SSI) problem. SSI effects on the dynamic response of the mid-rise reinforced concrete structures placing on silty sand soil under different earthquake motions for both actual system and scaled test model were directly analyzed by using 2D finite element method under plane-strain condition. Three different earthquake acceleration records as Chi-Chi (1999), Loma Prieta (1989) and Kocaeli (1999) have been considered at the bedrock level of the soil-structure system for this study. In the first phase of this work, the representation capacity of the employed scaling factor of 1:45 are evaluated by comparing the structural lateral displacements obtained from the fixed-base and flexible base analysis for full-scale field conditions with those for scaled test model to be experimentally examined in the small-capacity shaking table. The scaled geotechnical model is composed of the undisturbed soil specimen taken from the real site and the laminar soil container designed to be formed of aluminum frames and rubber layers. Afterward, the obtained results from the scaled numerical model of the soil-structure coupled system have been validated and verified by those of employing experimental shaking table tests. According to the obtained numerical and laboratory test results, it is concluded that the carefully selected large geometric scale coefficients for the soil-structure model used in the small-scale shaking table experiments can capture the dynamic response of the full-scale soil-structure system with acceptable accuracy. It is clearly observed that the local soil properties have considerably amplified the earthquake response of the structures in comparison to the fixed base structure. Furthermore, the structural behavior is significantly affected by the frequency content of the earthquakes considered in the SSI problem.

Design and Experimental Verification of a 1/20 Scale Model of Quayside Container Crane Using Distortion Theory

The scale model is an effective method to research the performance of quayside container crane (QCC) under the seismic condition, but the model distortion usually exists in the similar design process which leads to the incomplete similarity between the scale model and prototype. In this investigation, the distortion theory and the prediction coefficient correction method are used to upgrade the quality of 1/20 QCC scale model and, then, the seismic response of the QCC prototype is obtained from the shake table scale model test. In the first step, the similarity ratio of the 1/20 QCC scale model is calculated by the similitude law and the size of scale model is obtained from the similarity constants. In the second step, the bending stiffness is selected and determined as the distortion term and, then, the relationship between the distortion coefficient and the prediction coefficient is obtained by the finite element prediction coefficient method. Furthermore, the three different scale models are manufactured and tested in the shake table experiment under different seismic conditions. It is found that the experimental test results are consistent with the numerical simulation results of the QCC prototype. It can be concluded that the QCC scale model can be used to predict the performance of the prototype under the different seismic conditions after corrected by distortion theory, and the distortion theory is an effective method to solve the incomplete similarity between the scale model and prototype.

An algorithm for data reconstruction from published articles – Application on insect life tables

AbstractData collection in life table experiments is generally time-consuming and costly such that data reconstruction of published information provides an avenue to access the original data for pu...

Numerical modeling of a tunnel in jointed rocks subjected to seismic loading

The studies on the performance of tunnels under static loads are reported extensively in the literature but their performances under dynamic loads are limited. The present study highlights some of the important aspects of jointed rock tunnels during seismic loading. The literature review provides a shake table experimental study of a jointed rock tunnel. A Universal Distinct Element Code (UDEC) model is developed from this shake table experiment. The model tunnel is subjected to a scaled input motion of the 1985 Mexico earthquake. The numerical results are validated systematically with the findings of the shake table experiment. Further, the developed numerical model is used to perform parametric studies to understand the effect of in-situ stress, joint angles, joint stiffness, and joint friction angle on the deformation and stability of the tunnel under the same earthquake input motion. It is observed that some joint angle combinations form a wedge that yields excessive deformation and subsequently a complete failure. An exponential decrease in deformation occurred in the tunnel as the joint stiffness increases. It is found that the shallow tunnels are more susceptible to damage under the action of earthquake loads.

Structural Damage Detection and Localization with Unknown Postdamage Feature Distribution Using Sequential Change-Point Detection Method

The high structural deficient rate poses serious risks to the operation of many bridges and buildings. To prevent critical damage and structural collapse, a quick structural health diagnosis tool is needed during normal operation or immediately after extreme events. In structural health monitoring (SHM), many existing methods will have limited usefulness in the quick damage identification process because (1) the damage event needs to be identified quickly, and (2) postdamage information is usually unavailable. To address these drawbacks, we propose a new damage detection and localization approach based on stochastic time series analysis. Specifically, damage sensitive features, which are extracted from vibration signals, follow different distributions before and after a damage event. Hence, we use optimal change-point detection theory to find the time of damage occurrence. Because existing change-point detectors require the postdamage feature distribution, which is unavailable in SHM, we propose a maximum likelihood method for learning the distribution parameters from the time-series data. The proposed damage detection using estimated parameters achieves optimal performance. Also, we utilize the detection results to find damage location without any further computation. Validation results show highly accurate damage identification in American Society of Civil Engineers benchmark structures and two shake table experiments.