Showing papers on "Dynamic load testing published in 1986"

Time domain flexural response of dynamically loaded single piles.

Abstract: Adopting a Winkler assumption, a simple mechanical soil model is developed for the flexural response analysis of dynamically loaded piles. The model is defined by examining a frequency-domain analytical expression of the dynamic response of a massless cylinder in an infinite previously developed medium. The expression is based on the plane strain assumption. Using this soil model, the time-domain transfer matrix is developed for the flexural response of a single pile. The steady-state harmonic response of a single pile is computed by both the present approach and a previously developed frequency-domain solution. Good agreement between the two computed results validates the present approach. The dynamic response of single piles subjected to the lateral impulse load is computed for piles in both homogeneous and inhomogeneous soil, in order to demonstrate the capability of the present approach. It is confirmed that the developed soil model and pile response formulation are very efficient in numerical computation.

Dynamic response of 3-D embedded foundations by the boundary element method

Abstract: The dynamic response of three-dimensional rigid embedded foundations of arbitrary shape, resting on a linear elastic, homogeneous, and isotropic half-space is numerically obtained. The foundations are subjected either to externally applied forces or to obliquely incident seismic body or surface waves of arbitrary time variation. The time domain boundary element method (BEM) is utilized to simulate the soil medium with the aid of Stokes' fundamental solutions. The dynamic response of the foundation-soil system is obtained in a step-by-step time-marching solution. Use of this time domain BEM requires a minimum amount of surface discretization only and provides the basis for an extension to nonlinear soil-structure interaction (SSI) problems.

Measured Lateral Response of Mass on Single Pile in Clay

Abstract: The results of dynamic lateral load tests on a cantilevered mass supported by a single 10.75-in. (273-mm) diameter steel pipe pile embedded in stiff, overconsolidated clay are presented. These tests were conducted to provide a basis for evaluation of mathematical models that predict the relatively low-frequency dynamic pile response that is representative of systems in which the primary resonance frequency is controlled by the mass and stiffness of the superstructure. Frequency sweep shear forcing functions were applied at the top of the mass, which simulated a simple structure. The responses of the pile-supported mass, points on the embedded pile, and points in the supporting soil were recorded to determine frequency response functions. Frequency response functions between the applied load and pile cap-mass were then examined to aid in the identification of the pile–soil system parameters which most strongly influence response. The measured pile cap frequency response function peak amplitude was 0.0022 in./lb (0.0126 mm/N), or about ten times the static flexibility, and the resonance frequency was approximately 2.2 Hz.

Deformation Mechanism in Asphaltic Concrete

Abstract: A theoretical approach is presented to describe the permanent deformation mechanism in asphaltic concrete subjected to traffic simulated dynamic loading. The approach is based on mechanical energy concepts and leads to a better realization of the rutting mechanism in flexible highway pavements. A power relationship between the rate of permanent strain accumulation and the number of dynamic load repetitions was derived. Two parameters were introduced in this relationship: exponential parameter “m” and intersection parameter “A.” The first parameter, m, is dependent on the material type. Parameter A is a function of stress‐strain pattern and intensity, stress level, and dissipated plastic strain energy during the dynamic loading. The derived relationship was experimentally verified with excellent correlation. Parameter m was showed to be constant for all samples of the same material tested under various conditions. Regression analyses showed that “A” was a function of the applied deviator stress and the res...

Dynamic Load Flow Technique for Power System Simulators

Abstract: This paper presents a dynamic load flow technique for power system simulators. The approach presented can be applied to a system when there is a net accelerating or decelerating power in the system. It possesses all the attractive features and basic structure of the normal fast decoupled method, and it does not depend on the selected reference bus. The modifications to the standard fast decoupled power flow algorithm are derived, and power system simulator implementation considerations are discussed. The algorithm has been tested on standard IEEE test cases and on a metropolitan utility 559 bus model. A numerical example of the above algorithm on the 559 test case is presented which demonstrates convergence characteristics and computation requirements of the proposed algorithm. These results are compared with those of normal fast decoupled load flow.

Process and apparatus for measuring the dynamic loads applied to a highway by the road traffic

Abstract: This invention relates to a process for measuring the dynamic load exerted on a highway by the axles of the vehicles circulating thereon. Two piezo-electric cables sensitive to the pressure of the axles, furnish, upon passage thereof, a weight information pulse and a speed information pulse, respectively. Signals representing respectively the area of the pulse and the duration of the time gap separating the pulses, are applied to a divider which effects the quotient thereof and furnishes a signal representing the dynamic load.

Fatigue test apparatus

Abstract: A fatigue test apparatus in which a specimen to be tested is attached at its ends to a pair of opposing pistons positioned within a pair of opposing cylinders. The cylinders are attached to a support frame such that the specimen is oriented substantially vertically. In a preferred embodiment, the specimen is enclosed in a heat chamber to test at high temperatures. Each of the pistons is attached to a shaft having a weight at its end and the weights are drivingly connected to a pair of shakers which are actuated to vibrate 180° out of phase with each other. The cylinders are pressurized to exert a static tensile load on the specimen, and the shakers are actuated to exert a dynamic tensile load which is superimposed on the static load and travels through the weights, shafts and pistons to the specimen. With this arrangement, the dynamic load is not transmitted to the support frame so that the vibration characteristics of the support frame do not affect the vibration behavior of the specimen, yielding a dynamic load source independent of static or thermal load sources. more accurate results. By varying the magnitude of the weights and the stiffness characteristics of the shafts, static, dynamic or thermal fatigue tests may be conducted on a specimen either singlely or in any combination with dynamic loads imposed at frequencies as high as 10,000 Hz.

Shear and Bending Response of a Rigid-Plastic Beam to Partly Distributed Blast-Type Loading

Abstract: A study is undertaken on dynamic response of a simply supported rigid perfectly plastic beam that is subjected to partly distributed blast-type pressure loading. The beam material has finite shear strength and obeys a square yield criterion relating bending moment and transverse shear force. The transverse dynamic load is uniformly and symmetrically distributed over a middle portion of the span. Various patterns of deformation, which combine plastic bending and shear sliding, are obtained for a wide range of parameters, and the effects of transverse shear forces and time dependence of the dynamic pressure are examined.

Flexibility coefficients and interaction factors for pile group analysis

Abstract: Flexibility coefficients of single piles and interaction factors established for groups of two piles are presented to facilitate analysis of arbitrary pile groups exposed to static horizontal loads...

Analysis of axial pile-soil interaction in clay

Abstract: A method for predicting the maximum mobilized side resistance and unit shaft resistance-displacement curves (load transfer functions) on piles in clay is described. The method was derived using a numerical solution to model pile installation effects and a finite element scheme to model pile loading. Results of three well-documented pile load tests on steel piles were used to develop intermediate steps and final solutions, and the method was verified by comparing predicted results to two other load tests. An expression is proposed to represent load transfer functins for use by practitioners for the design of bridge and other foundations in clay.

Multi-range load cell

Abstract: This invention is to provide a load cell with a composite elastic body that is the I-shaped spoke whell structure. It can easily be used as dual, three, or four range load cell in which each range has the beginning of zero load and can be used for measuring the static load or the dynamic load. As a result, the range can be divided into several zones, in the situation of measuring the continuous load with larger changable amplitude the load cell possesses higher measuring precision to each zone of the full range measured. This cell can be installed to use in any angle from the vertical direction to the horizontal direction.

Design criteria for roadway supports to resist dynamic loads

Abstract: Conditions under which dynamic loads occur in mines are briefly described and the special vulnerability of roadways in coal mines to fail under dynamic load is considered. A method for assessment of shock load energy anticipated is proposed, based on the volume of rock and the velocity of rock particles induced by rapid rock failure and/or seismic tremors. Case examples from Upper Silesian coal mines are given and the safety factor of steel supports against the shock energy from rockbursts is discussed. The shock energy damping ability of various parts of steel supports and support systems is calculated as a basis for rational support design. Results of six mine experiments where various types of roadway support were installed and then loaded dynamically by blasting within surrounding rocks are discussed.

Method and buffer apparatus for preventing corrosion in dynamic load bearing assembly

Abstract: A method and buffer apparatus for preventing corrosion in a dynamic load bearing assembly. A resilient buffer material is compressively adjustably positioned between a pair of dynamic adjacent load bearing components in a machine such that the amount of electrical resistance between the load bearing components can be varied without having to disassemble the machine. The buffer material is maintained in position between the load bearing components by compressing the buffer material an amount equal to 5 to 30% of its length to outwardly expand surfaces of the buffer material against the load bearing members.

Starvation effects on the hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

Abstract: The effect of inlet starvation on the hydrodynamic lubrication of lightly loaded rigid nonconformal contacts in combined rolling and normal motion is determined through a numerical solution of the Reynolds' equation for an isoviscous, incompressible lubricant. Starvation is effected by systematically reducing the fluid inlet level. The pressures are taken to be ambient at the inlet meniscus boundary and Reynolds' boundary condition is applied for film rupture in the exit region. Results are presented for the dynamic performance of the starved contacts in combined rolling and normal motion for both normal approach and separation. During normal approach the dynamic load ratio (i.e. ratio of dynamic to steady state load capacity) increases considerably with increase in the inlet starvation. The effect of starvation on the dynamic peak pressure ratio is relatively small. Further, it has been observed that with increasing starvation, film thickness effects become significant in the dynamic behavior of the nonconformal contacts. For significantly starved contacts the dynamic load ratio increases with increase in film thickness during normal approach and a similar reduction is observed during separation. A similar effect is noted for the dynamic peak pressure ratio.

Predicted effect of dynamic load on pitting fatigue life for low-contact-ratio spur gears

Abstract: How dynamic load affects the surface pitting fatigue life of external spur gears was predicted by using the NASA computer program TELSGE. Parametric studies were performed over a range of various gear parameters modeling low-contact-ratio involute spur gears. In general, gear life predictions based on dynamic loads differed significantly from those based on static loads, with the predictions being strongly influenced by the maximum dynamic load during contact. Gear mesh operating speed strongly affected predicted dynamic load and life. Meshes operating at a resonant speed or one-half the resonant speed had significantly shorter lives. Dynamic life factors for gear surface pitting fatigue were developed on the basis of the parametric studies. In general, meshes with higher contact ratios had higher dynamic life factors than meshes with lower contact ratios. A design chart was developed for hand calculations of dynamic life factors.

Dynamic Analysis of an Elevated Water Tower Subjected to Wind Gust

Abstract: The analysis of a column carrying a concentrated mass and subjected to a dynamic load is presented in its general form. The water tower is given as a specific example. Despite the singularity in the mass distribution function of the system, a closed form solution to the response problem is obtained. The Green function for the differential problem has been developed thus making the analysis applicable to any dynamic load.

Dynamically loaded pile in overconsolidated clay

Abstract: A series of dynamic axial loading tests were conducted on a 273-mm-diameter steel pipe pile driven 13.4 m into a layered deposit of overconsolidated clay. A linear inertial mass vibrator was used to provide frequency sweep loadings from frequencies above to frequencies below the fundamental frequency of the pile-soil-cap system at three magnitudes of dynamic load. Superposition of a dynamic component of load of about 5% of the static capacity of the pile on a static biased compressive load resulted in slight nonlinear behavior and induced some residual increase in flexibility of the system. Two existing analytical models were studied in light of the measured performance of the pile and were found to yield appropriate solutions provided the soil parameters were selected properly.

Analysis of Dynamic Laterally Loaded Pile in Clay

Abstract: Analyses of a dynamic lateral load test conducted on a full-sized pipe pile supporting a rigid cap-mass superstructure are described. Three algorithms representing different categories of mathematical models that simulate pile-soil interaction were employed in the analyses. These algorithms represented: (1) a hysteretic subgrade reaction model capable of modeling gap formation; (2) a fully coupled subgrade reaction (boundary element) model that accounts for nonlinear behavior; and (3) an approximate (plane strain) linear model. Input parameters were varied for each of the models in order to develop an appreciation for appropriate inputs. All of the models were found to yield reasonable, but not exact, correspondence with frequency response functions at the location of the cap-mass measured during sweep loading of the cap-mass. Inputs necessary to obtain such correspondence were found that were predicated upon field measurements or upon published criteria. System damping was predicted to be too low with all models, with the exception of one set of inputs for Model (1) based on comparisons of the band widths of the predicted and measured frequency response functions.

Dynamic Plastic Analysis of Impulsively Loaded Viscoplastic Rectangular Plates With Finite Deflections

Abstract: An energy balance method for the dynamic plastic analysis of thin rectangular plates made of a strain-rate sensitive material, taking into account the influence of finite-deflections, is proposed. The particular case of a fully clamped plate under uniformly distributed dynamic pressure pulse or blast loading is studied in some detail. In addition to the nonaxisymmetric and dynamic nature of the problem, the analysis considers important nonlinearities in the strains, equilibrium equations, and constitutive equations. Nonlinear ordinary differential equations in various regimes of plate deflections and loading histories are derived and solved using a Runge–Kutta method. Comparisons are made with existing experimental data.

Tremor, Effect of Physical Load and Reproducibility

Abstract: The effect of three kinds of moderate physical loads on the tremor of the middle finger was studied in eight males: 1) cycling 15 min on an ergometer at a heart rate of 140 beats/ min (general dynamic load); 2) lifting a mass of 1 kg by the middle finger at a rate of 30 times/ min for 5 min (local dynamic load); and 3) carrying in each hand a 15 kg mass for 5 min. Few effects were observed: 10% decrease of RMS acceleration after local dynamic load and some changes in the power spectrum after general dynamic load. It is concluded that the effect of recent, short time physical load of moderate extent can be neglected as a disturbing factor in the study of the effects of toxic exposure on postural tremor. The inter- and intra-individual variation (over 4 weeks) in nine males and nine females also was studied. The intra-individual variation ranged from 4% for the mean frequency to 35% for the 0-4 Hz band of the power spectrum. The inter-individual variation ranged from 8% for the mean frequency to more than 6...

Role of Load Tests in Friction Pile Design

Abstract: In situ measurements of stresses and pore pressures on a model pile shaft, the Piezo‐Lateral Stress (PLS) cell, are combined with theoretical analyses to reconstruct the conditions of a large‐scale pile load test at a site in Empire, LA. Results show that the mode of penetration of open‐ended piles has an important effect on the performance of pile shafts. Pile plugging during driving retards the rates of soil consolidation and the gain in shaft capacity after installation. The Empire experience is used to identify important factors affecting shaft‐soil interaction which require control and/or evaluation during pile load tests. Methods of enhancing the value of pile load test data in the future are recommended.