Showing papers on "Dynamic load testing published in 1999"

The statistical properties of host load

Abstract: Understanding how host load changes over time is instrumental in predicting the execution time of tasks or jobs, such as in dynamic load balancing and distributed soft real-time systems. To improve this understanding, we collected week-long, 1 Hz resolution traces of the Digital Unix 5 second exponential load average on over 35 different machines including production and research cluster machines, compute servers, and desktop workstations. Separate sets of traces were collected at two different times of the year. The traces capture all of the dynamic load information available to user-level programs on these machines. We present a detailed statistical analysis of these traces here, including summary statistics, distributions, and time series analysis results. Two significant new results are that load is self-similar and that it displays epochal behavior. All of the traces exhibit a high degree of self-similarity with Hurst parameters ranging from 0.73 to 0.99, strongly biased toward the top of that range. The traces also display epochal behavior in that the local frequency content of the load signal remains quite stable for long periods of time (150-450 s mean) and changes abruptly at epoch boundaries. Despite these complex behaviors, we have found that relatively simple linear models are sufficient for short-range host load prediction.

Optimal topology design of structures under dynamic loads

Abstract: When elastic structures are subjected to dynamic loads, a propagation problem is considered to predict structural transient response. To achieve better dynamic performance, it is important to establish an optimum structural design method. Previous work focused on minimizing the structural weight subject to dynamic constraints on displacement, stress, frequency, and member size. Even though these methods made it possible to obtain the optimal size and shape of a structure, it is necessary to obtain an optimal topology for a truly optimal design. In this paper, the homogenization design method is utilized to generate the optimal topology for structures and an explicit direct integration scheme is employed to solve the linear transient problems. The optimization problem is formulated to find the best configuration of structures that minimizes the dynamic compliance within a specified time interval. Examples demonstrate that the homogenization design method can be extended to the optimal topology design method of structures under impact loads.

Permanent strains of piles in sand due to cyclic lateral loads. technical note

Abstract: The strain superposition concept, proposed for ballast study, is applied in this note to evaluate strain accumulation for laterally loaded piles in sand. It is shown that the soil properties, types of pile installation, cyclic loading types, pile embedded length, and pile/soil relative stiffness ratio are important factors that influence the pile behavior under mixed lateral loads. These factors are quantified by means of a degradation factor, t, which is derived from the results of 20 full-scale pile load tests and then verified using six additional full-scale pile load tests.

Permanent Strains of Piles in Sand due to Cyclic Lateral Loads

Abstract: The strain superposition concept, proposed for ballast study, is applied here to evaluate strain accumulation for laterally loaded piles in sand. It is shown that the soil properties, types of pile installation, cyclic loading types, pile embedded length, and pile/soil relative stiffness ratio are important factors that influence the pile behavior under mixed lateral loads. These factors are quantified by means of a degradation factor, t, which is derived from the results of 20 full-scale pile load tests and then verified using 6 additional full-scale pile load tests.

Impact Loads due to Wheel Flats and Shells

Abstract: A Finite Element (FE) model of vehicle-track system is employed to duplicate the experiments carried out by British Rail and CP Rail System. The theoretical results of the wheel/rail contact forces, rail-pad forces and strains in the rail showed very good correlation to the experimental data. Extensive results are compared with experimental data in the time domain for through validation of the developed model. The characteristics of the impact loads due to wheel flats and shells are investigated based on the validated FE model. The study shows that the shape and size of flat or shell, axle load, vehicle speed and rail-pad stiffness mainly affect the impact loads. Adding elastomeric shear pads on the wheelset bearing does not reduce the wheel/rail dynamic contact force but it may reduce the dynamic force on the bearing. Reducing rail-pad stiffness to a certain level on a concrete-tie track may significantly reduce the dynamic load and the force transmitted to the concrete tie.

Measured time effects for axial capacity of driven piling

Abstract: The results of a study to quantify effects of time on pile capacity are presented herein. The main focus of this paper is to present results from a database developed from various pile tests reported in the literature and to present some observations based on the pile test data. Both sands and clays are shown to experience setup. A database containing 80 pile load tests (both static and dynamic) was collected and sorted into three groups according to the primary subsurface profile: sands, clays, and mixed soil. Capacity-versus-time relationships are plotted for each soil type, but particular attention is given to the increase in capacity of pile in sand with time. It is shown that the load test results can provide an upper-bound estimate and a lower-bound estimate. Estimating the effect of time on pile capacity in sand can be important for reuse of existing piling and also can be helpful for quantifying just how much to expect capacity to increase with time if pile load tests show that capacities are comi...

Inelastic Dynamic Response of Structures Using Force Analogy Method

Abstract: A new algorithm based on the force analogy method for studying the inelastic structural behaviors subjected to dynamic loadings is proposed. Inelastic analysis is performed based on varying the structural displacement field, which differs from the conventional method of changing stiffness. Each inelastic deformation of the structure is denoted as a degree of freedom, and therefore all inelastic behaviors are represented by a single equation. The algorithm is very time efficient because only initial stiffness is used, and it achieves high numerical accuracy when incorporating the use of a state space numerical integration method in dynamic analysis. Moreover, this algorithm is dynamically stable in analyzing structures with not only strain-hardening properties, but also elastic-plastic properties and strain-softening properties. Comparison between the proposed algorithm and an existing inelastic dynamic analysis software program is performed to demonstrate the accuracy and efficiency of this algorithm. Finally, application of the proposed algorithm to the dynamic response of a six-story hospital building is presented to show the complete inelastic analysis procedure in analyzing realistic structures.

Necking bifurcations during high strain rate extension

Abstract: Dynamic necking bifurcations which occur during rapid plane strain extension of a block of strain hardening plastic material are investigated. The block is presumed to be a portion of a plate or thin-walled shell deforming at high strain rate. It is found that the rates of growth of both very long and very short wavelength modes of nonuniform deformation are suppressed by inertia, thus promoting a necking pattern at an intermediate wavelength. The analysis indicates that, for blocks of small aspect ratio, the number of necks formed per unit length is proportional to the square root of the mean extensional strain rate of the block. The results of the analysis agree with necking patterns observed in high velocity ring expansion experiments and in detailed numerical simulations.

Centrifuge modelling of pipe piles in sand under axial loads

Abstract: A series of model pile tests have been performed in the geotechnical centrifuge at the University of Western Australia to study the behaviour of driven piles in homogeneous sand. Open, sleeved and closed-ended piles have been driven by a miniature pile driving actuator into silica flour of varying densities. The model pile was fully instrumented, allowing strain gauge data to be monitored during dynamic and static testing. Analysis of the load tests revealed that the shaft friction increased approximately linearly with depth at a low rate, but with a marked increase close to the pile tip. The average shaft friction for the closed-ended tests was shown to be greater than for the open-ended tests. For all tests, the average values of shaft friction were greater than those suggested by current guidelines for design of offshore piles (API RP2A), and the ratio of tensile to compressive shaft capacity was always below unity. The end-bearing resistance normalized by the cone tip resistance was shown to reduce wi...

ELISA: An estimated load information scheduling algorithm for distributed computing systems

Abstract: In this paper, we present a decentralized dynamic load scheduling/balancing algorithm called ELISA (Estimated Load Information Scheduling Algorithm) for general purpose distributed computing systems. ELISA uses estimated state information based upon periodic exchange of exact state information between neighbouring nodes to perform load scheduling. The primary objective of the algorithm is to cut down on the communication and load transfer overheads by minimizing the frequency of status exchange and by restricting the load transfer and status exchange within the buddy set of a processor. It is shown that the resulting algorithm performs almost as well as a perfect information algorithm and is superior to other load balancing schemes based on the random sharing and Ni-Hwang algorithms. A sensitivity analysis to study the effect of various design parameters on the effectiveness of load balancing is also carried out. Finally, the algorithm's performance is tested on large dimensional hypercubes in the presence of time-varying load arrival process and is shown to perform well in comparison to other algorithms. This makes ELISA a viable and implementable load balancing algorithm for use in general purpose distributed computing systems.

Effect of various dynamic loads on stress and strain behavior of a Norfolk sandy loam

Abstract: Field traffic by heavy agricultural machinery can cause serve structural degradation of arable land. This may result in surface runoff, restricted availability of water, oxygen and nutrients to plant roots and therefore in reduced crop yields. In order to prevent these impacts and to develop appropriate counter-measures the complete compaction process must be understood. In this study the effect of increasing dynamic loads on the stress and strain relationship was examined using a stress state transducer (SST) attached to a displacement transducer system (DTS). Three different dynamic loads, ranging from 13.2 to 25.3 kN, were applied each by two passes on a firm sandy loam (Typic Kandiudults) at 10% wheel slip. During the first pass the calculated major principal ( σ 1 ), mean normal (MNS) and octahedral shear stresses (OCTSS) increased significantly with increasing dynamic loads. For the second pass in contrast to these calculated stress values, except the major principal ( σ 1 ), were not affected by the applied dynamic loads. While the vertical displacement of the transducer during the first pass was more than doubled with each dynamic load step, the soil volume element above the transducer was vertically deformed at a constant rate of 25%, independent of the dynamic load. Since no further vertical deformation of this soil volume element was induced by the second pass and additional vertical soil movement was detected, soil compaction is expected to progress to deeper soil layers as the dynamic load and the wheeling frequency increases. Thus the reduction of wheel loads and the avoidance of repeated wheeling events in one tire track may contribute to a sustainable land management of firm soils.

Nonlinear Structural Response of Laminated Composite Plates Subjected to Blast Loading

Abstract: We are concerned with the theoretical analysis of the laminated composite plates exposed to normal blast shock waves as well as presenting correlation between the theoretical analysis and the experimental results of the strain time histories. The laminated composite plate is clamped at all edges. On the theoretical side of the study, dynamic equations of the plates are derived by the use of the virtual work principle within the framework of the Love theory of plates. The geometric nonlinearity effects are taken into account with von Karman assumptions. Then the governing equations of the laminated plate are solved by the Runge-Kutta-Verner method. A new displacement function is considered for the theoretical solution of the blast-loaded clamped plate. Furthermore, finite element modeling and analysis for the blast-loaded composite plates are presented. On the experimental side of the study, tests have been carried out on the laminated composite plates with clamped edges for two different blast loads. The results of theoretical and finite element methods are compared with the experimental results. Theoretical and finite element analyses results are in a good agreement. There is a qualitative agreement between the analyses and experimental results in the first load case. The predicted peak strains and response frequency are in an agreement with the experimental results for first load case. Thus the theoretical solution may be used for providing material in the preliminary design stage. There is a difference between the analysis and experimental results in the second load case because of the extremely large deflections. In this study the effects of loading conditions, geometrical properties, and material properties are separately examined on the dynamic behavior, as well.

Spectral-Element Method for Levy-Type Plates Subject to Dynamic Loads

Abstract: Spectral-element method (SEM) is applied for the vibration analysis of the Levy-type rectangular plates subject to distributed dynamic loads In the solution procedure, both FFT and inverse FFT computer algorithms are efficiently used to obtain the dynamic responses in time domain Distributed dynamic load is approximated, as the superposition of equivalent dynamic line loads and the spatial coordinate dependence of equivalent line loads is removed by (spatial) FFT This procedure transforms the original plate (two-dimensional) problem into an effective beam (one-dimensional) problem so that the solution procedure for one-dimensional structures can be used Numerical tests show that SEM provides very accurate solutions when compared with conventional finite element solutions

Numerical Procedure for Predicting Pile Capacity—Setup/Freeze:

Abstract: In geotechnical engineering practice, the increase over time of pile capacity after installation is sometimes referred to as pile setup or freeze. Pile setup, which is often associated with piles driven into saturated clays and silts, is mainly attributed to soil consolidation around the pile. Field observations have shown that pile setup is significant and continues to develop for a long time after pile installation. Pile foundations are usually expensive. Therefore, taking a small percentage of pile setup into consideration will result in cost reduction and savings in piling projects. This paper presents a general numerical procedure to predict pile setup by simulating the behavior of the pile during its different life stages: installation, subsequent consolidation, and loading. The Hierarchical Single Surface modeling approach, the strain path method, and the nonlinear finite element analysis of porous media were used in the analyses. The procedure was verified by successfully predicting the field behavior of pile segment models installed into soft marine clay. Numerical experiments were also conducted to demonstrate the applicability of the numerical procedure to full-scale driven piles. Piles with diameters of 0.3 m and 0.5 m and a length of 10 m were considered in the analyses.

Study of the mechanical properties of plain concrete under dynamic loading

Abstract: A new testing methodology based on the Hopkinson bar principle is proposed for studying globally and locally the mechanical properties of plain concrete at a high strain rate. A Hopkinson bar bundle measures the local mechanical characteristics over the cross section of a large specimen of plain concrete subjected to impact loading. With this method, more accurate measurements of the stress-strain diagram are obtained, especially during the fracturing phase of the concrete specimen.

On the interaction and branching of fast running cracks—a numerical investigation

Abstract: Phenomena of dynamic fracture in brittle materials resulting from the interaction of fast running cracks are investigated numerically. These studies concern the influence of mutual shielding on crack paths, the stress intensity factor and crack tip speed variations, the stability of a simultaneous propagation of several cracks, and the interaction of cracks of different size. Furthermore, dynamic crack branching is investigated from a macroscopic point of view. The respective initial boundary value problem of linear elastodynamics is formulated as a system of time-domain boundary integral equations in conjunction with experimentally motivated criteria for crack growth and branching. The numerical evaluation is based on a boundary element method and an appropriate discretization of the fracture and branching criteria. Results obtained from numerical simulations are discussed with regard to the experimental findings.

Quasi-static and dynamic shearing of sheet metals

Abstract: The test results of quasi-static and dynamic plane simple shear are discussed. Use is made of a new double-shear device in which loading and displacement are controlled in compression. First a series of quasi-static tests with a servohydraulic universal machine was performed. After that, two types of tests were made: i) the device with an attached double-shear specimen was placed between two bars of the split Hopkinson pressure bar; ii) direct impact was assessed on the shear device placed in front of the transmitter Hopkinson tube. The relevant initial-boundary value problem of the simple shear has been formulated, and the numerical solution compared with experimental data. An exceptional homogeneity of the permanent strain was observed in experiments and numerical simulation. For deformations larger than 0.7, zones of strain localization were observed.

Dynamic and Static Load Testing of Model Piles Driven into Dense Sand

Abstract: Systematic studies of pile response during static and dynamic load tests are generally too expensive to conduct in the field, and at model scale may be limited by scaling effects and the ability to obtain accurate stress waves. This paper describes such a study, conducted at model scale in a geotechnical centrifuge, for piles driven into dense sand. Adverse scaling effects were minimized by the use of extremely fine sand (silica flour), and accurate stress waves were obtained using high-frequency data logging, together with a Hopkinson bar arrangement for the measurement of pile-head velocity. The overall aim of the study was to compare dynamic and static test data, for open- and closed-ended piles driven into dense sand, for a range of delivered hammer energies. Open- and closed-ended model piles were driven into dense sand and statically load tested at different penetrations, without stopping the centrifuge. Stress-wave data were collected, during continuous driving and from single blows immediately prior to the commencement of static load testing. An assessment of the accuracy of the mobilized soil resistance estimated from dynamic testing, using different levels of analysis, has been made by direct comparison with the static load test data. Particular emphasis has been placed on the performance of the dynamic analyses in light of different driving conditions and delivered hammer energy. From measurements of the delivered hammer energy, the efficiency of the centrifuge pile driving system was also assessed.

Prediction of pile setup in clay

Abstract: Reliable calculations of pile setup times represent a critical parameter in the design of large-diameter pipe piles that are used to anchor offshore tension leg platforms. Predictions of setup times can be obtained by analyses that simulate the changes in effective stresses and soil properties occurring around a single pile during installation and subsequent equilibration of excess pore pressures. Pile installation is modeled using the framework of the strain path method, assuming that there is no plugging of soil within the pipe pile. Changes in effective stresses and soil properties at all stages of the analysis are described by the MIT-E3 soil model, with input parameters derived from laboratory tests on high-quality samples. After installation, the analyses solve the radial dissipation of excess pore pressures around the pile shaft and setup of effective stresses in the soil by nonlinear finite element methods. Dissipation times are controlled by the pile aspect ratio (ratio of diameter to wall thickness), in situ effective stress, stress history, and hydraulic conductivity of the clay. This paper illustrates the validation of the proposed setup analyses with data from instrumented model piles and pile shaft elements at two well-documented test sites.

Dynamic Load Allowance for Through-Truss Bridges

Abstract: The objective of the present study was to experimentally evaluate the statistics of dynamically induced stress levels in steel through-truss bridges as a function of bridge component type, component peak static stress, vehicle type, and vehicle speed. Better understanding of critical bridge rating parameters will enable more accurate bridge evaluations of this type of structure. Three 60-year-old, steel through-truss bridges with similar characteristics were investigated in the present study. Several bridge components on each of the three bridges were instrumented (truss members, stringers, and floor beams), and dynamic strain data were collected under controlled and normal traffic conditions. The dynamic strain histories were processed to obtain bridge component peak static response and peak dynamic response, resulting in the determination of the dynamic load allowance (DLA) for each of the instrumented bridge components for each of several truck crossings. The calculated DLA values are plotted as a function of member peak static stress for each bridge member instrumented. The DLA data are examined as a function of component type, component location, truck type, number of axles, truck speed, and truck direction. This study has demonstrated that the DLA is dependent on truck location, component location, component type, and component peak static stress but appears to be nearly independent of vehicle speed.

Power system dynamic load modeling using adaptive-network-based fuzzy inference system

Abstract: The representation of the dynamic characteristics of power system loads is widely used for obtaining power system operations, controls and stability limits and becomes a critical factor in power system dynamic performance. In this paper, the performance of power system dynamic load modeling using adaptive-network-base fuzzy inference system (ANFIS) is compared with traditional architectures. The ANFIS models can represent nonlinear systems performance accurately, and they are promising for dynamic load models. Computer simulations show excellent results using this approach for power system dynamics.

The dynamic effects of conventional freight car running over a dipped- joint.

Abstract: Available experimental data of the dynamic force at a rail joint are used to validate the Discrete Support (DS) model of vehicle-track system. The validated DS model is employed to investigate the characteristics of dynamic forces due to a dipped rail joint. The results show that increasing axle load and rail equivalent mass significantly increases the first peak load. The wheel (unsprung) mass, stiffness of bearing rubber pad, and ballast stiffness mainly affect the second peak load. Properly designing a profile near the rail joint may reduce the dynamic load at the joint. The results obtained also indicate that the dynamic load generated at one wheel partially transmits to a neighboring wheel.

A geometric approach for establishing dynamic buckling loads of autonomous potential two-degree-of-freedom systems

Abstract: Nonlinear dynamic buckling of autonomous potential two-degree-of-freedom nondissipative systems with static unstable critical points lying on nonlinear primary equilibrium paths is studied via a geometric approach. This is based on certain salient properties of the zero level total potential energy surface' which in conjunction with the total energy-balance equation allow establishment of new dynamic buckling criteria for planar systems. These criteria yield readily obtained exact' dynamic buckling loads vithout solving the highly nonlinear initial-value problem. The simplicity, reliability, and efficiency of the proposed technique is illustrated with the aid of various dynamic buckling analyses of two two-degree-of-freedom models which are also compared with those obtained by the Verner-Runge-Kutta scheme.

Hierarchical dynamic state estimator using ANN-based dynamic load prediction

Abstract: The paper presents a new scheme for dynamic state estimation in power systems. The dynamics of the power system are modelled more realistically using artificial-neural-network-based bus-load prediction and load flow for state prediction. At the filtering step a hierarchical model which incorporates the measurement function nonlinearities is used. This considerably reduces the computational effort, making the proposed scheme suitable for on-line application. Test results for an IEEE 118-bus test system are presented to show the characteristics of the present method.