Showing papers on "Dynamic load testing published in 1983"

A study of dynamic wheel forces in axle group suspensions of heavy vehicles

Abstract: A wheel force transducer was used to measure dynamic wheel loads for speeds ranging between 40 km/h and 80 km/h over road surfaces ranging from as-new construction to the maximum tolerable roughness as measured using the NAASRA roughness meter. The effects of tyre inflation pressure and axle group load were taken into account and a factorial experimental design was used to determine dynamic loading, expressed as a form of coefficient of variation termed the dynamic load coefficient (dlc), as a function of speed and roughness for each suspension type. It was found that, for practical purposes, the dlc for each suspension type is a function of the product of the speed and the square root of the NAASRA roughness value. The centrally-pivoted drive axle suspensions (walking beam and single point types) show a dlc increasing with spring stiffness. Although the trailer suspensions and the torsion bar drive axle suspension showed, in general, lower dlc's than the centrally-pivoted drive suspensions, it was concluded that the level of dynamic loading generated by all suspensions is large. Three out of five drive axle suspensions were found to cause severe dynamic pavement loading. At least one of these does not comply with current Australian regulations for load sharing suspensions, and a quantitative test of dynamic loading is suggested. Most suspensions were found to share the load between the wheels to within 10 per cent of an equal share and this level is proposed as a quantitative criterion of load sharing ability. One currently accepted type did not load-share adequately and it is concluded that a test is needed and in some cases proper fitment of the suspension to the chassis needs to be ensured. (Author/TRRL)

On the application of the mode‐acceleration method to structural engineering problems

Abstract: Mode-superposition has been extensively used in computing the dynamic response of complex structures. Two versions of mode-superposition, namely the mode-displacement method and the mode-acceleration method, have been employed. The present paper summarizes the results of a systematic study comparing the accuracy of the mode-displacement and mode-acceleration methods when applied to structures with various levels of damping or various excitation frequencies. The paper also discusses several details concerning the implementation of the mode-acceleration method.

Cavitation in fluid‐structure response (with particular reference to dams under earthquake loading)

Abstract: The paper presents a general procedure for dealing with coupled fluid-structure interaction under dynamic load. This incorporates a facility for dealing with a cavitating fluid and is based on the Newton displacement potential. Several solutions are obtained for two-dimensional gravity dam problems illustrating the effects of cavitation on earthquake response and blast loading.

Ultimate Pile Capacity for Eccentric Inclined Load

Abstract: The ultimate bearing capacity of rigid piles and pile groups in sand has been determined under various combinations of eccentricity and inclination of the load varying from the vertical to horizontal directions. The results of load tests on single model piles and free‐standing groups are compared with theoretical estimates. The influence of eccentricity and inclination of the load on the bearing capacity can be represented by simple interaction relationships between the ultimate loads and moments and between the axial and normal components of the ultimate load. The effect of a pile cap resting on the soil in piled foundations is examined on the basis of previous theory and model test results.

Shaft vibration evaluation

Abstract: A shaft vibration evaluator employs measured displacement of a shaft in the vicinity of a bearing together with known or measured shaft eccentricity to calculate the dynamic bearing load so that damaging loads can be avoided. Shaft vibration or motion is assumed to be elliptical having major and minor axes which are inclined at angles with respect to the bearing displacement sensors. The magnitude of the major and minor axes and the angular displacement are calculated from the measured parameters and provide one set of inputs to the load calculator. Bearing eccentricity can be calculated from a knowledge of shaft speed, lubricant temperature and known bearing geometry. For a given eccentricity, a set of four damping coefficients and four spring coefficients of the bearing may be derived. These coefficients are the remaining inputs to the dynamic load calculator.

Dynamic uplift capacity of helical anchors in sand

Abstract: Earth anchors are becoming a very useful technique for securing temporary and permanent foundation systems subjected to uplift loads. In recent years, helical anchors have become more widely used because of their ease of installation and low cost. Past research has concentrated on static loading. Recent investigations into the cyclic capacity of anchors have increased rapidly due to increased construction in the ocean and the importance of anchors in advancing offshore technology. Laboratory tests were performed with one-quarter scale single-helix model anchors in dry sand at a constant relative density and embedment depth. The two parameters investigated were the displacement amplitude and prestress load. Appropriate equipment and instrumentation were used to monitor anchor deflection, dynamic load, and horizontal soil stresses during the cycle tests. Static tests were performed to determine the ultimate pullout capacity of dead anchors and the postcyclic failure capapcity of anchors. It was concluded that screw-in anchor installation technique and the application of a prestress load both produced an increase in horizontal soil stresses and soil densification in the vicinity of the single-helix anchor. Cyclic loading caused a reduction in horizontal stress and an upward cyclic creep of the anchor. Reduction of horizontal stress occurred until the active failure stress was approached. At this point, the sand had loosened and the anchor began to pullout rapidly. The post-cyclic static capacity was found to be lower than the ultimate static capacity of a dead anchor. In the prestress range investigated, a critical ratio of dynamic load to effective static capacity exists. Above this critical ratio, a failure of a prestressed anchor will occur earlier than a dead anchor failed by cyclic loading. Prestressed anchors below this critical ratio will experience an increase in anchor life.

The dynamic collapse of a column impacting a rigid surface

Abstract: An analytical investigation has been made of the dynamic collapse of an elastic periodically supported column having an attached mass at one end and impacting a rigid surface at the other end with prescribed velocity and angle of incidence. The investigation has been carried out using a first-order approximate nonlinear solution and a nonlinear finite element solution. The first-order approximate solution has led to the determination of four basic nondimensional parameters which govern the response. These parameters include mass, impact velocity, initial imperfection, and impact angle parameters. Three regions of these parameters have been identified in which the character of the column's response is markedly different. These regions have been designated as the linear, transition, and dynamic collapse regions. Threshold values of the parameters which separate these regions have been defined. Results obtained reveal that responses in the linear region are dominated by axial motion, those in the transition region exhibit some axial-flexural coupling, and those in the collapse region are dominated by flexure. The rebound velocity in the transition and dynamic collapse regions is shown to be less than that predicted by the linear dynamic solution. The dynamic peak axial compressive load in the transition region is shown to be the same as that predicted by the linear dynamic solution. In the collapse region, the peak load decreases to a value less than the linear dynamic value, but greater than the static Euler buckling load. Moreover, it is shown that whereas the peak axial compressive load predicted by the linear solution grows unbounded with increasing values of the mass parameter, an ultimate dynamic load value is approached in the collapse region.

Static and dynamic behavior of mechanical components associated with electrical transmission lines

Abstract: This article describes the behavior of transmission towers, insulator strings, conductors, and foundations as determined from theoretical analyses, model testing, and full-scale tests. Line vibration is also briefly reviewed.

Bridge Dynamic Tests: Implications for Seismic Design

Abstract: A five span, 400 ft (120m) long, reinforced concrete box girder bridge supported on single column piers, which are pile founded, was subjected to extensive dynamic tests. The pullback and quick release method of excitation was used. Two D-8 crawler tractors were used to apply total release loads which had a magnitude of about one-quarter of the earthquake design loads. System identification techniques were used to extract the experimental in situ dynamic stiffness of the pier pile group foundations from the suite of field data. An independent geotechnical analysis of the bridge's pile foundations yielded pile group stiffness which were in acceptable to good agreement with the experimentally determined values. Moreover, this analysis indicated that for design level seismic loadings the pile group stiffnesses are quite deflection dependent. It was further shown that it is essential to include the soil-structure interaction effect in the analytical model if correct distributions of seismic loads are to be obtained.

Dynamic Elasto-Plastic Model for Reinforced Concrete Members

Abstract: It is becoming increasingly necessary to investigate the strength of reinforced concrete structures subjected to dynamic loading. Experience and knowledge relating to the non-linear dynamic behaviour of such structures is still limited, however. Attempts to solve this type of problems with the aid ofa finite element approach soon encounter difficulties. An example of this consists in the correct representation of the appropriate collapse mechanism and more particularly in the problem of the numerical stability for the integration process required for solving the equations of motion with respect to time and made additionally awkward by the non-linear behaviour. These problems are associated with mathematical algorithms and are not relevant to the structural problem under investigation. The authors anticipate considerable improvement in this sphere in the future, but at present they prefer an approximation which provides direct insight into the response of structures without involving too many difficulties with numerical problems. For this reason a simple well-tried beam model is applied. This discrete beam model consists of a number of indeformable segments (the elements) with hinges (the nodes) at their ends andjoined to one another by means of flexural springs. The mass of each segment is conceived as concentrated in the hinges, as is also the dynamic load. The material properties are assumed to be elasto-plastic. The effect of loading rate on the material properties has also been taken into account. Two failure criteria are applied in the discrete mathematical model. Thus, in the elastic range (M < Mp) the concrete section is checked for strength, and in the plastic range the rotational capacity is not allowed to be exc~eded. In other words, the shear strength (loadbearing capacity in shear) is calculated as a function of the moment-shear combination that occurs. The treatment of the subject starts from formulae derived for static moment-shear combinations. It emerges that the (static) formula given by Rafla can be modified and suited to dynamically loaded structures (M < Mp). The effect of shear on the permissible rotational capacity can be expressed in a simple relation. Thus, the rotational capacity will have its maximum value if the shear force is zero; but the presence of shear force will reduce the rotational capacity. The discrete model described here has been applied to analysing the elasto-plastic response of a beam subjected to an impulsive load. Two different examples are presented. The first example is concerned with the response ofa simply-supported beam under a uniformly distributed impulsive load. It appears that the distributions of the bending moments and shear forces are very different from those obtained for a comparable static load. Presupposing that no shear failure will occur (adequate shear reinforcement), plastic moments will be formed at some distance from mid-span. From here the plastic hinges will then move towards the middle of the span. The second example considers a beam with fixed (fully restrained) ends. It approximately represents a strip of the roof of a road tunnel. The situation where a gas explosion occurs in the tunnel is investigated. The distribution of the bending moments which is then produced bears a closer similarity to that associated with a static load, but the shear forces are still different, though less so than in the case ofthe simply-supported beam. Ifno stirrups are provided, a shear failure criterion must be introduced. This will very greatly reduce the permissible explosion load, so that in most cases no plastic hinges will even be formed.

Experimental investigation of the deformation of thin plates under static loading and interaction with a shock

Abstract: Modern bonded composites disclose broad possibilities for the creation of effective structures in various branches of engineering. To use the potential possibilities of composite structures, their thorough investigation under static and dynamic loads is necessary. Considerable attention has recently been paid to the analysis of multilayer composite

Estimating the Severity of Shaft Vibrations Within Fluid Film Journal Bearings

Abstract: Proximity probes are being widely used in turbomachinery to measure the amplitude of shaft vibrations within fluid film bearings. There has been, however, little information available for judging the degree of severity of such vibrations. The present paper provides an analysis which correlates shaft vibration amplitude with some basic bearing parameters—allowable dynamic load on the bearing, its size, geometry, and operating conditions. Curves are provided for several bearing geometries which can be used for a rational estimate of allowable shaft vibration levels.

Design aspects of energy absorption in car pedestrian impacts

Abstract: The car-pedestrian impact is formulated as a design task for the engineer designing a car front. Pedestrian load tolerances are defined in an appropriate form for design. A two dimensional mathematical model with assumed deformable car surface is used to determine the movement of the pedestrian during the collision, the locations and velocities of impact. The dynamic load bearing capacity of materials and car body components is determined using an impact pendulum. With the described design procedure an experimental front was defined, built and tested in full scale crash tests. Results are presented. Emphasis is laid on simplicity of design methods as well in analysis as in experimental testing.

Dynamic Behavior of Straight Bevel Gears of Gleason Type

Abstract: Dynamic behavior of straight bevel gears of Gleason type was investigated by measuring the dynamic load, circumferential, radial and axial vibration accelerations of gears and noise under different running conditions. It was found that the root stress ratios of maximum dynamic root stress to static one in the toe, middle and heel of a straight bevel gear tooth are almost equal and that the circumferential, radial and axial vibration accelerations of gears are coupled to each other. The circumferential vibration acceleration is considered to be the first source of the vibration and noise.

Fundamental Properties of Soils for Complex Dynamic Loadings: Dynamic Constitutive Modeling of Sandy Soils.

Abstract: : Constitutive modeling of cohesionless soil for both standard static test conditions and insitu impulsive dynamic load conditions is discussed in this annual report Predicted laboratory response for several different types of models is evaluated using data from a coordinated testing program The modeling of insitu soil response to explosive events (CIST and DISC Test) is considered, and the laboratory-derived models are tested for their convenience and accuracy in predicting ground motions Several important laboratory and insitu phenomena which were not reflected by the model exercises are discussed Based on the conclusions from this study, testing and modeling requirements for dynamic loading situations are proposed

Fat embolism after static and dynamic load. An experimental investigation.

Abstract: Rabbit femora were fractured with different strain rates (static and dynamic) with measurements of the bone marrow pressure during the actual moment of fracturing. The results show that the amount of fat emboli is dependent on the strain rate, and occurs at the moment of fracture, when elastic strain energy is released in the form of pulse waves.A further group of rabbit femora were subjected to standardized pulse-waves on the bone marrow. The number of fat emboli produced was proportional to the strength and number of these waves.

A method for static and dynamic load analysis of standard and modified spur gears

Abstract: The mesh stiffness and dynamic load characteristics for several cases of the Normal Contract Ratio and High Contact ratio gearing. The considered contact ratios were grouped in the general range of 1.7,2.0, and 2.3. The HCR gearing is defined by contact ratios equal to or greater than 2.0. The HCR gearing is represented by a group of small pressure angle, fine pitch, and long addendum gearing.

Deep foundation design in the new Ontario Highway Bridge Design Code: Reply

Abstract: A review is presented of some aspects of deep foundation design in the new Ministry of Transportation and Communications of Ontario, ultimate limit states Bridge Design Code. The design of axial pile capacity distinguishes between structural capacity limit and geotechnical capacity limit. The geotechnical capacity of a driven pile is governed by the dynamic impedance of the pile cross section. Higher geotechnical capacity, for instance due to soil setup, can only be utilized if proven to exist. Different capacity modification factors are used for routine load tests and high level test loading. Modern methods of dynamic monitoring are included and capacity determination by such methods is accepted as equivalent to determination from routine load tests. Lateral capacity of single piles and group piles, downdrag, and inclined loading of pile groups are considered, as are details such as splicing and use of pile shoes. Pile spacing is given as a function of expected pile length.

Dynamic load torque measuring apparatus for rotary machine

Abstract: PURPOSE:To enable continuous measurement of nonsteady dynamic load torque characteristic from the static condition to the steady operation by introducing detection output to a dynamic load torque computation circuit detecting a vibrating acceleration and a rotary phase in an unbalanced surface. CONSTITUTION:The sine value and the cosine value of a rotary phase detected with a rotary phase detector 6 are computed 9 and 10 separately. The sine value is multiplied 11 by a vibrating acceleration detected with a vibrating acceleration detector 7 while the cosine value is multiplied 12 by an vibrating acceleration detected with a vibrating acceleration detector 8. Then the output of the multiplication 12 is inverted 13 and added 14 to the other multiplication output. The addition output is applied to an arithmetic circuit 15 to multiply the unbalanced quantity me times and a dynamic load torque TDL is measured.

The mechanics of splitting a strip through penetration with a sharp wedge

Abstract: This paper deals with the mechanics involved in splitting a strip through penetration with a sharp wedge along the center line. First, a quasi-static problem is considered. The crack propagation can be associated with the loss in stability when the applied load reaches the critical value for bifurcation. Next, the static problem is extended to a dynamic case by including the inertia force of the wedge in the analysis. An initial value problem is formulated for the motion of the wedge. For any given weight of the wedge, the critical velocity of the wedge for indefinite crack propagation can be determined by means of the theory of dynamic stability. Finally, the case of splitting a strip under repeated applications of impulsive load is considered. The critical number of applications of impulsive load for indefinite crack propagation is determined numerically.

Mathematical Modelling of the Load Bearing Characteristics of a Dynamically Driven Pile

Abstract: The purpose of the present paper is to describe a numerical method for the prediction of the load/displacement characteristics of a partially or fully embedded dynamically driven pile. The system is modelled mathematically so that the soil displays idealised hysterisis in its behaviour while the pile is assumed to be made of relatively rigid elastic segments. Generalised dynamic relationships are applied to the system and a microcomputer is used to provide a numerical solution. Despite the apparently involved representation of the problem the program was kept in its simplest form. A number of examples were examined using the formulation, the results for which are commented upon in the text.