Showing papers on "Dynamic load testing published in 1979"

Analysis of single piles under lateral loading

Abstract: The behavior of laterally loaded piles was investigated using the finite difference computer program COM623. A thorough search of the literature was undertaken to find the results of lateral load tests performed in clay and sand. The results of these analyses indicate that most of the p-y criteria, where p is the lateral resistance against the pile in force per unit of length and y is pile deflection, are satisfactory in predicting pile behavior. A modification of the p-y criteria of Reese and Welch (1975) was suggested, based on the results of some of the analyses presented in this report. (FHWA)

A simple approach to pile design and the evaluation of pile tests

Abstract: In the past, the design of a pile in a given soil against undue settlement has entailed lengthy numerical analysis for a variety of pile geometries. Similarly the back analysis of load tests on piles has usually been accomplished by repeated analysis with differing soil stiffness profiles in order to arrive at the profile which gives best agreement with the measured results. The recent development of an approximate closed form solution for the problem of a vertically loaded pile has enabled these two processes to be considerably simplified. The present paper takes the solution as developed and extends it to the case of piles bearing on a stiffer stratum of soil. The solution may then be used both for the design of single piles and also for the back analysis of pile tests. For given soil conditions, it is possible to draw up design charts showing how the settlement of a pile may vary with load level and pile geometry. This process is demonstrated for some typical soil conditions. For evaluating load tests, the closed form solution may be manipulated to give an immediate estimate of the average soil stiffness down the pile for the case of tests on uninstrumented piles. If additional information (such as the settlement of the pile base) is available, it is possible to obtain an estimate of the soil stiffness profile down the length of the pile without recourse to a computer. Examples of some actual pile tests are given.

Fatigue loading of cantilever sign structures from truck wind gusts

Abstract: This is the final report of an experimental and analytical study to determine the fatigue loading on cantilever highway signs from gusts produced by trucks passing under the sign. Three sign structures were instrumented in the field to determine their response from truck gusts. These signs were then analyzed using a three-dimensional dynamic analysis computer program. A loading was developed from the computer analysis which produced a response which simulated the response measured in the field study. A matrix of standard Texas State Department of Highways and Public Transportation standard sign structures was analyzed using the same computer program and the simulated loading. The result of this analysis was the development of dynamic load factors for these signs. A simple method of estimating the three primary modal frequencies of typical signs was developed using single degree of freedom models. Means of correcting the results of these simple models to agree with the computer analysis was developed. The resulting frequencies allow the dynamic load factor to be calculated without the use of the complex three-dimensional computer analysis. A method of analyzing the anchor bolts of the signs for fatigue is presented. The analysis uses the loading developed in this study amplified using the dynamic loading factors calculated from the modal frequencies estimated from the single degree of freedom models. The low measured stresses in the superstructure did not indicate any potential fatigue problems. The anchor bolt fatigue stresses are primarily caused by bending of the bolt between the base plate and the foundation. (FHWA)

Combined Effects of Dynamic Load and Travel Reduction on Tire Performance

Abstract: TESTS on selected pneumatic tractor tires for vari-ous soil conditions show that dynamic load, as well as travel reduction, plays an important role in deter-mining tractive performance. The data indicate that in many field conditions tractive efficiency could be improved by selecting an appropriate dynamic load for a particular soil condition.

Interpretation of Load Tests on High-Capacity Driven Piles

Abstract: Pipe piles and H-sections about 35 m (115 ft) long were driven through 24 m (80 ft) of alluvial materials to bearing in a stratum of glacial till about 15 m (50 ft) thick overlying bedrock. Load tests were conducted to establish the equipment and driving resistance needed to develop a capacity of 3560 kN (400 tons) solely in the underlying tills. Interpretation of these tests proved to be a challenge that led to the development of a new technique to analyze load transfer using only data obtained from conventional pile load tests. Among the conclusions reached were (1) ultimate shaft friction of steel piles driven into very stiff to hard tills did not exceed 120 kPa (1.25 tsf); (2) for piles as large as 460 mm (18 in.) in diameter, ultimate shaft friction is not necessarily mobilized before the pile capacity is reached; and (3) loading and unloading a pile can cause irreversible changes in the existing as well as on the ultimate shaft friction-methods of interpreting pile load tests to determine load transfer or residual stresses that rely on these changes being negligible, should be used with caution.

Analysis of Load Tests on Instrumented Steel Test Piles in Compressible Silty Soil

Abstract: Axial compression and tension tests were performed on two end-bearing piles (one pipe and one H-pile) and two friction piles (one pipe and one H-pile) 3 months after they were driven through a granular test fill into compressible clayey silts. In analyzing the behavior of the piles, skin friction equations were developed based upon effective stresses in the soil, the soil-pile friction factor and the Poisson's ratio of the pile. These equations satisfactorily estimated the distribution of negative skin friction loads mobilized on the piles before they were test loaded and the skin friction mobilized in the axial compression and tension pile tests at failure. The equations were also applied to some well-documented pile tests, and showed that the skin friction that can be mobilized to resist axial compression loading can be estimated from pullout tests. This paper discusses the pile test procedures and the observed relative movements between the pile tips and the surrounding soil at various loads applied to the piles and describes a laboratory test method for measuring the coefficient of friction between the pile and the soil.

Assessment of hybrid model for pile groups

Abstract: The effects of mathematical modeling of pile groups by representing the soil response against the piles through unit-soil-resistance relationships for isolated piles and using elasticity methods to account for group effects were studied by modeling three pile-group tests in clay reported in the literature. Emphasis is placed on the effect of varying the Young's modulus of the soil surrounding the piles and the effects of imperfect pile alignment. The errors in computed cap translation were small; and the errors in load distribution to piles and the axial load distribution along the piles were insignificantly affected by the value of the modulus and could not be eliminated by this modeling method. (Authors)

A Rational Procedure for Evaluating the Behavior of Impact-Driven Piles

Abstract: A numerical solution has been developed using a finite difference formulation to simulate the one-dimensional impact wave propagation behavior and subsequent static load test performance. Based on this solution, the importance of residual driving stresses in properly interpreting pile behavior under axial loads is examined. This paper (1) briefly describes the analytical procedure developed by the authors to incorporate residual stresses explicitly, (2) applies the procedure to a documented pile load test to demonstrate the concepts developed, (3) examines the consequences of ignoring residual driving stresses in interpreting/predicting pile behavior under axial loads, and (4) demonstrates the influence of various parameters on the predicted pile performance.

Influence of Driving Stresses on the Development of High Pile Capacities

Abstract: The impact stresses have been measured near the top of piles as they are driven to practical refusal in very dense granular soils and shale bedrock. These stresses have been compared with capacities determined from staticload tests. The comparisons were carried out on 24 piles of various types and lengths driven with a wide range of hammers and capblocks at different sites. They indicate that the ultimate bearing load divided by the pile shaft cross-sectional area during driving averages 1.2 times the impact stress at practical refusal with a standard deviation of ′20 percent. This is in close agreement with the Case method wave equation analysis. It is concluded that, for conditions similar to those tested, driving criteria to establish a required bearing load may be estimated from impact stress measurements at the top of the pile. Other methods, such as conventional dynamic formulas, are not as suitable, as they cannot measure the effects of hammer and cap block variations.

Interpreting End-Bearing Pile Load Test Results

Abstract: Interpretation of pile tip settlement behavior obtained from rod telltales on fourteen full-scale test piles at five different sites indicates that the applied load can be divided into end-bearing and skin friction components. The end-bearing component is used to obtain stiffness information about the bearing stratum. An equation for estimating pile settlement based on information accumulated during this study is given, and a procedure is proposed to estimate settlement from downdrag forces. Information about bearing strata obtained from the load test results can be accumulated and used to assist with design of future end-bearing pile foundations.

Dynamic response of concrete railway bridges

Abstract: The dynamic load factor of concrete railroad bridges when subjected to trains moving at various speeds is investigated. The theoretical study includes effects of speed, wheel loads, axle spacing, span lengths, bearing pads, bridge weight and track modulus. Data from 23 existing single-span bridges was used to develop dynamic characteristics. Results indicate that dynamic load factor is not simply a function of live load, dead load, train speed or span length, but a function of the dynamic characteristics of both bridge and loading. While calculated dynamic load factors compare favorably with field data of prestressed concrete bridges obtained by AAR, there is little correlation between results of this study and AREA recommendations for impact factor on such structures.

Load tests on friction piles in sand. field tests with different test procedures

Abstract: In Sweden pile load tests are often performed to determine the design length of friction piles in clay and sand. These load tests are normally performed on two test piles before the construction of the piling. For the load tests a number of test procedures have been used such as the CRP-method the ml-method and the cyclic loading and unloading test method. In order to find out if there are any differences between the test results derived from the different test procedures, a series of pile load tests with different test procedures on half-scale piles was performed. At the load tests four different test procedures were used. (1) load test with constant rate of penetration (CRP), (2) maintained load test (ml), (3) cyclic loading and unloading test (cyclic) and (4) load test according to ASTM. The following conclusions can be drawn from the test results. (a) the ml method gives greater settlements for a certain load than the CRP method. (b) the load settlement curves for the cyclic loaded and unloaded piles also show greater settlements for a certain load than the CRP-method.(C) the yield load determined from the cyclic loading and unloading test is on average 30% lower than the ultimate bearing capacity (pb90) determined from the CRP tests. (D) the ASTM gives hardly any information on the ultimate bearing capacity of the pile. (e) a pile which has previously been load tested settles less than a pile which is loaded for the first time and (F) if a friction pile in sand is redriven 0,2 M after a load test the influence of the previous load test is eliminated. (TRRL)

Pile capacity - a reliability approach

Abstract: To account for the variability of soils over large depths it is desirable to use probabilistic methods to estimate the load carrying capacity of the piles A reliability based method is proposed using monte carlo simulation technique A parametric study is carried out for piles in clays and sands and the importance of parameters like cohesion, adhesion, angle of shearing resistance, length to diameter ratio of pile, etc, Highlighted Results are presented in the form of plots between probability of failure and normalized load (a)

Static and Cyclic Axial Load Tests on a Fully Instrumented Pile

Abstract: The results of static and cyclic axial pile load tests performed on a fully instrumented steel H-pile driven into a glacial till deposit are presented. Cyclic loads were applied through a hydraulic system interfaced with an automated electronic-electromechanical closed loop servo system to achieve a controlled load intensity to the pile in a specific shape (sinusoidal) at specific frequency (0.1 Hz). The load-deflection, load transfer, and configuration of the pile during pile driving and after each load increment was measured through an instrumentation system that consisted of load cells, deflectometers, strain gages, accelerometers, and inclinometers. Data obtained in this investigation indicated that: 1. Axial deformation of the pile remained essentially constant prior to and after cyclic axial load application. The behavior of the pile was essentially elastic during cyclic load application. 2. Within the scope of testing performed, cyclic vertical load increments do not effect the load carrying capacity or load transfer characteristics of the pile. 3. Load transfer characteristics varied with the magnitude of applied axial load. The ratio of point bearing resistance to the applied load increased with the applied load. However, the rate of increase generally decreases with increasing applied load.

Experimental tests concerning the biomechanical behaviour of pertrochanteric osteosyntheses.

Abstract: The biomechanical behaviour of pertrochanteric fractures stabilized by means of an angled plate or flexible condylar nails was characterized by mechanical testing The stability and the types of motion occurring under dynamic load in the vicinity of the fracture and the effect on the implant were examined The mechanical test results corroborated clinical experiences In the case of extramedullary anchorage of implants, stability under load is possible only if an intact cortex on the medial side of the fracture guarantees the bearing of compressive load With flexible condylar nails, however, it is possible to achieve a permanent load capacity up to approximately 100 kp, even if medial support is lacking, by putting the fracture in a valgus position so that the load-bearing arm is shortenedIt was also possible to estimate the actual loading on the operated leg within the immediate postoperative phase by means of the “stabilization effect”

An investigation of the dynamic and static stresses in universal bearing H-piles

Abstract: As part of continuing research on steel bearing piles, an investigation was carried out by British Steel Corporation in an attempt to gather data which will illuminate the areas of contention for limiting stress levels to be raised, thereby allowing economies to be made and customers' confidence to be increased in selecting steel bearing piles for a particular application. To assess the characteristics of dynamic and static loading, a strain gauge measurement technique was used. Blow by blow stress analyses were carried out. In total 700 blows were examined. The full record of 700 blows and static observations can be obtained from The We/ding Research Department, of BSC's Teeside Laboratories, Middlesbrough. The results reveal that during the course of driving the pile through hard strata, the impact stresses were 0.6 to 0.7 times the minimum yield stress, at the last blow. These impulsive stresses had no discernable effect on the structure of the piles. Results obtained suggest that considerable increase in design stresses might safely be adopted for steel bearing piles. One of the aims of this long term research is to produce a dynamic testing system which gives more accurate results than can be obtained from traditional methods.

Pile Load tests to evaluate load transfer mechanisms

Abstract: Load transfer mechanisms in 17 test piles are evaluated by means of an extensive monitoring program during full-scale load testing and are compared with behavior computed by a displacement compatibility analysis. H-piles,Raymond step taper piles, auger-cast piles, and steel pipe piles were tested, in many cases to failure. These piles were installed at a power generating station in saprolites of the Piedmont Province of Georgia. Deflection was measured at the butt of each pile and at the tip and one or two intermediate levels in most piles by means of telltales. A boring and laboratory testing program was an integral part of the program. Load transfer mechanisms are evaluated by means of a displacement compatibility analysis using results of the field and laboratory investigations. Good agreement between computed pile behavior and that determined by the monitoring program during load testing is demonstrated. The results of the monitoring program and the enhanced understanding of the load transfer mechanisms involved make a comparison of the effectiveness of the various pile types possible and allow development of rational installation criteria.

Transport container with dynamic load supports - rests on bearings carrying load and has insulating material in walls and at bearing surfaces

Abstract: The transport container may be mounted onto a vehicle or fitted to a container frame - The container is fitted with two separate support fittings, one for static loads and the second for dynamic loads. The container rests on bearings carrying the load and has side support elements to distribute the load. The container is also fitted with insulating material in the walls and at the bearing surfaces. The outside mounting supports are designed as shock absorbers to clamp out oscillations set up in the container.

Wood Beams under Impact Load

Abstract: An analysis of the behavior of glue-laminated wood beams under impact load in the elastic and plastic range is presented. The theoretical part of the study consists of the definition of the general methodology of solving the vibration of the system with a nonlinear ratio between force and deformations. The validity of the vibration design is verified by a testing program using full-size specimens. The test results obtained agree favorably with the theoretical predictions. There is good coincidence in the elastic range between the actual and theoretical dynamic characteristics. There is a discrepancy between measured deformations under static and dynamic load in the plastic range. The theoretical dynamic characteristies with and without damping coincide well with the corresponding real dynamic characteristics and the theoretical method given may be used in the plastic range.

Bearing load measuring method of rotary shaft

Abstract: PURPOSE:To enable conversion into bearing load, display, record, and monitor, and prevent accident of rotary machine, by detecting the oil film pressure of oil film bearing on a rotary shaft CONSTITUTION:One or plural pressure taps 3, 3', 3'' are provided in an oil film bearing 1 of a rotary machine, from which a guide tube is led, and a pressure detector 5 is connected behind a valve 4, and electric signals are taken out from a transducer 6 On the other hand, a thermocouple 7 and an amplifier 8 are provided to detect the temperature of the bearing oil film Besides, in order to take out the rotating speed signal, a rotation detecting device 9 is provided These signals are led from a static load converter 10 out into a static load display device 13, and, in order to improve the frequency characteristic, is guided from a dynamic load converter 11 into a dynamic load display device 14 through a frequency characteristic converter 12 The signals inputted into the display devices 13, 14 are inputted into discriminator and recorder If abnormality is found, necessary signals are sent into an alarm device or a stopping device 16, so that adequate countermeasures may be done

Analytical Methods to Predict Pile Capacities

Abstract: A comprehensive test pile program was conducted for a large manufacturing facility. During this program, several pile types, including timber, precast concrete, concrete-filled pipe, and shells were driven and load testedto failure. Prior to load testing, the ultimate pile capacity was predicted by three static and two dynamic techniques. After testing, the predicted and measured capacities were compared. The wave equation and the Dutch cone penetration soundings resulted in the most consistent predictions.

The dynamic loading performance of heavy vehicle suspensions

Abstract: The present experimental study of heavy vehicle axle groups and the dynamic loads they develop is placed in the context of the NAASRA economics of road vehicle limits study and the subsequent requirement for load equalisation within an axle group. Dynamic loading in axle groups is reviewed. The dynamic load coefficient is defined. A generalised configuration for suspensions common in Australia is developed. Basic suspension dynamic effects are discussed with special reference to inter axle oscillation, and evidence of an important suspension role in dynamic pavement loading is examined. An experiment involving a walking beam tandem axle fitted with a wheel force transducer is described. Results are presented for the dynamic load coefficient as dependent on NAASRA roughness value of the pavement, vehicle speed and tyre inflation pressure. The significance of these results for the ongoing program involving a range of common suspensions is discussed, as is an extension to the experimental capability in terms of a second wheel force transducer. It is concluded that vehicle speed and road roughness interact strongly with the walking beam tandem axle to produce high levels of dynamic loading. The tyre inflation pressure also appears to have an important effect in terms of the vehicle bounce mode.

Load Testing of Instrumented 225-Foot-Long Prestressed Concrete Piles

Abstract: Piles driven through 62 to 77 m (200 to 250 ft) of low-strength clay penetrated up to 23 m (75 ft) into compact fine sand with little increase in driving resistance. At other locations, the piles met refusal after only about 1 m (3.3 ft) of penetration into the sand. Borings indicated a consistently compact bearing stratum. This test program was developed to establish whether piles driven to very low driving resistances at moderate penetration into the lower compact sands would support the 91-Mg (100-ton) design load. The overlying clays provided no permanent pile support, as in some areas they are underconsolidated as a result of site filling. The test program included casting eight electric strain gages and a 7.6-cm (3-in.) diameter hole in 36-cm (14-in.) square prestressed concrete piles. The piles were driven in three sections to low driving resistances with a continuous record of driving stresses. Anchors were installed in the center hole, with rods extending to the surface. The top of the piles were loaded in increments to 3½ times the design load to overcome the loss of load into the thick clay layer. A procedure of performing the load test a short time after the pile was driven and cyclic loading after reaching maximum test load was used to increase the load reaching the lower compact sand stratum. Full-scale laboratory load tests were preformed on a section of pile to establish the variation in elastic modulus to permit accurate estimates of pile load at various depths. The pile load tests demonstrated that the deep compact sand layer was capable of supporting the design loads, even though penetration was terminated at low driving resistances. Substantial portions of the load during the short-term tests were resisted by adhesion in the thick clay layer. The amount of clay adhesion was directly related to the time after driving of the piles.

A program for calculating load coefficient matrices utilizing the force summation method, L218 (LOADS). Volume 2: Supplemental system design and maintenance document

Abstract: The LOADS computer program L218 which calculates dynamic load coefficient matrices utilizing the force summation method is described. The load equations are derived for a flight vehicle in straight and level flight and excited by gusts and/or control motions. In addition, sensor equations are calculated for use with an active control system. The load coefficient matrices are calculated for the following types of loads: (1) translational and rotational accelerations, velocities, and displacements; (2) panel aerodynamic forces; (3) net panel forces; and (4) shears, bending moments, and torsions.