statnamic, the engineering of art, p. middendorp

Sixth International Conference on the Application of Stress-Wave Theory To Piles 1

Orlando, Sao Paulo, 2000.

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1 INTRODUCTION

Art was of minor interest to the author when he was starting his engineering study at the Technical Uni-versity. Within a short time his interest got a strong impulse when he met his present wife, a painter and artist, at that time studying at the Royal Academy of Art in The Hague. After assisting here with some projects he experienced that the logical thinking of engineers is in no way superior to the associative and intuitive thinking of artist in finding practical solutions, but that both are complimentary and when combined into an artist-engineer as a person or a team, can result in marvels.

In the 15

th century the artist-engineer, was a so-

cially prominent and respected figure, commissioned by powerful and wealthy patrons, well paid and of-ten regarded as one of the brightest ornaments in sovereign courts. The most famous example of course is Leonardo da Vinci (P.Galluzi, 1996).

Because of cultural changes and specialization a

gap has been generated between engineering and arts and most engineers are not aware nowadays of their artist-engineer forefathers.

Still a strong interest of artists for engineering can

be observed in modern art, for example Panameren-ko (1996). The artist-engineers are still among us and it was the privilege of the author to cooperate for long period with one of them: Patrick Berming-

ham, the inventor of Statnamic and the nowadays President of the Berminghammer company.

During his career the author was impressed by the

many creative solutions of engineers all over the

Statnamic, the engineering of art

P. Middendorp TNO Profound, The Netherlands

ABSTRACT: In present standard engineering practice there seems to be a big gap between engineering and art. It is the experience of the author that engineering and art can exist as an excellent combination. This will be illustrated by examples from history and the authors personal experience. One example will be treat-ed extensively: the continuous development of the Statnamic load testing method as a marvelous combination of engineering and art. The start of the Statnamic concept is described as an interaction between an artist and engineers together with developments on the theoretical approaches and technical applications. Further the present Statnamic state of the art will be discussed briefly.

Figure 1. Leonardo da Vinci. Automatic file-making machine



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world. Many engineers are not aware that their crea-tive solutions can be considered art and that they act

as engineer-artist. In this paper the author wants to illustrate his view by using the Statnamic develop-ment as an example in which one artist-engineer and many engineer-artist contributed with creative ideas and solutions.

The Statnamic development will be described by

introducing the start of Statnamic together with some milestones, theoretical approaches and tech-nical applications. Further the present research and developments will be mentioned and problems that still have to be solved.

2 THE STATNAMIC CONCEPT

Patrick Bermingham (1998) got the first idea about the Statnamic concept in Hamilton in 1985 while watching a static load test with kentledge, when he first thought about utilizing the inertia of the kent-ledge (Fig. 2).

According to Fellenius (1995) the idea for the Stat-namic concept was born in 1987 when he asked Pat-rick Bermingham to design a drop hammer for im-pacting a pile to perform dynamic load tests. The

idea of Fellenius at that time was that dynamic pile testing would become independent of the piling con-tractor, the pile driving rig, and in many instances contractors unionized labor, as well make him and others free to perform dynamic load testing after a good and long set up time. This idea was not original because several such devices were already around, but Fellenius just needed a local practical tool.

At that time Bermingham had just finished a pro-

fessional education as a sculpturer in London and worked also for the Bermingham pile driving and hammer manufacturing company. From his child-hood on Patrick was interested in both engineering and art and supplied, for example, several ideas for improvement to the Berminghammer pile driving hammers.

It was not such a strange idea that the Berming-

hammer Company chose Patrick to come up with a design for a drop hammer. Patrick contacted Felle-nius and suggested a pile loading system design from a fully different viewpoint compared to stand-ard engineers.

Why do engineers want to drop the weight, why

do they not send it up into the air?

Intuitively he converted Newtons Law from

Force = Mass times Acceleration

To

Mass times Acceleration = Force (Load) This concept needed a few months to evolve and

Figure 3. First Statnamic device with accel-erometer and early catch mechanism.

Figure 2. Early sketch of a Statnamic piston and cylinder arrangement by Patrick Bermingham



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Bermingham made a first prototype (Figure 3) and started experiments by shooting masses upwards in Hamilton, Ontario in April 1988. He determined the feasibility of accelerating a mass upwards from the top of the foundation rather than dropping a mass onto the foundation

Bermingham also tried out several concepts of catching the reaction mass when falling back from launching and also here creative ideas from the art-

ist-engineer can be observed, especially the gravel catching mechanism based on the reliable gravity of the earth (Fig.4). With the gravel mechanism a grav-el container is placed around the reaction mass and the space between gravel container and reaction mass is filled with gravel. During testing four suc-cessive stages can be distinguished. In stage 1 the Statnamic device is ready for launching. In stage 2 the reaction mass is launched upwards by high-pressure gases. During this stage the pile is loaded and a Statnamic test performed. Because of the mo-mentum the reaction mass will remain moving up-ward in stage 3 and the gravel will flow under the reaction mass and over the pile head because of gravity. In stage 4 the reaction mass will fall back and will be caught by the gravel inside the container and the impact load will not be transferred to the pile head but to the subsoil. This creative, simple and el-egant principle is still applied as one of the methods in absorbing the energy from the falling reaction mass.

Bermingham presented his results and ideas to

several parties and also to the author at the OTC (Offshore Technology Conference) at Houston in 1988. Based on the combination of his engineering background and experience with ideas of artists, the author immediately recognized the beauty and pow-er of Bermingham's idea for pile testing applications.

Berminghammer and TNO agreed to start a joint

development and decided to do the first prototype testing immediately after the Third Stress Wave Conference at Ottawa in 1988. With the help of Fokke Reiding and Matthew Janes they realized that the long duration feature of the load allowed a fully different approach in instrumentation and analysis compared to dynamic load testing.

It was decided to base the load measurement on a

calibrated load cell, to make the measurement inde-pendent from pile material properties and to measure displacement directly by the use of an electronic theodolite. The electronic theodolite was a rather expensive instrument and a new tool for measuring displacement was developed based on a laser and a laser sensor, which is still in use. So the basis of measurements became load-time signals and dis-placement-time signals similar to static load testing.

3 FIRST DEVELOPMENTS

In May of 1988 the first model tests where per-formed with instrumentation provided by T'NO. These first two days of testing confirmed the ability of the very small Statnamic device to produce loads of up to 5 tons with duration of up to 30 ms. From

Figure 4. First Statnamic trial tests.

Figure 5. Successive stages of Statnamic

Testing.



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this point onwards the direction of Statnamic was upwards. A second model was built and sent to TNO in Holland where the instrumentation would be developed. In the laboratory at TNO, Statnamic tests were performed using a calibrated load cell and a new laser measuring system developed specifically for the Statnamic test. Both measuring systems worked very well the first day and they have re-mained virtually unchanged to this date.

The next step was to build a Statnamic tester,

which incorporated the instrumentation and was large enough to test a real pile in the ground. A 0.6 MN tester was built, which was one tenth of full scale, but still able to test small piles driven into real soil. This load-testing device was first used to test piles in the Berminghammer yard in Hamilton, McMaster University, and Ashbridges Bay. Since that time it has performed tests in Europe, Japan, and the United States. The primary objective of this equipment was to prove the durability of the instru-mentation in all weather conditions, and to prove the practicality of the equipment in the field. This equipment was also used to make the first compari-sons between conventional static load tests and the new load test method. The 0.6 MN device proved that Statnamic testing could be performed in all types of adverse weather including rain and snow. It also proved the simplicity and practicality of the sys-

tem in the field and the first load test comparisons proved an unexpectedly close agreement with con-ventional static load tests. The success of this first prototype enabled Berminghammer to manufacture of a full-scale 5MN tester.

Statnamic was first called Inertial load testing (Bermingham, P., et all., 1989. The author gave the method its present name Statnamic, realizing that the method was positioned between Static load test-ing and Dynamic load testing.

From the very beginning Statnamic was an inter-

national development rather than a regional or na-tional development. Testing of driven and cast insi-tu piles was carried out in Canada, Holland, Germany and the United States during the first two years.

At this time all of the testing was conducted with

the aim of gaining a better understanding of the be-havior of piles subjected to very quick loading cy-cles. Statnamic and static load tests were conducted side by side as well as on the same pile in as many different soil types as possible. Every effort was made to collect as much data as possible and to avoid making predictions about the static behavior of a foundation until we could collect a wide range of test results. Today many companies and universi-ties are still collecting and expanding this worldwide database.

The first two years of research revealed a great

deal about pile behavior when subjected to a Stat-namic load of 120ms duration. It was observed that in the elastic range there was a very good agreement between static load deflection and Statnamic load deflection, it was observed that in very soft soils and clays it was possible to apply a much larger load Figure 6. Patrick Bermingham launching a

0.6MN device

Figure 7. Set up of a 5MN Statnamic device with gravel catch mechanism



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than a static load prior to plunging the pile. In stiff non-cohesive soils and rock sockets it was observed that there was very close agreement between Stat-namic load test results and static load tests per-formed along side. It was also observed that the se-quence of loading a foundation had a great effect on the perceived similarity of test results and this had to be taken into account. It was also observed that dur-ing a typical Statnamic test the pile would reach maximum displacement at some time after peak force had been applied. In other words the pile would continue to move downwards while the ap-plied load at the pile top was decreasing. At the point where the pile reached maximum displacement the velocity of the pile was zero and then the pile would begin to rebound as the load was further de-creased. This observation which was present in nearly all test results except very stiff piles on rock, lead to the development of the Unloading Point Method (UPM) by the author (P. Middendorp, 1992).

4 METHODS OF ANALYSIS

From the very start of development there has been a determined effort to make Statnamic a means of measuring rather than a prediction method. This has meant putting a very strong emphasis on using accurate measuring equipment and recording equip-ment. The measured data will then be more reliable and may then be examined more closely. From the beginning we have been observing the behavior of foundations subjected to very rapid loading with a view to being able to better understand the mecha-nism of failure during a Statnamic test. In the end it is hoped that Statnamic testing will stand alone as a rapid test with a distinct method of analysis, which will measure the load deflection behavior and de-termine the factor of safety of the foundation.

Initially no attempt was made to convert the re-

sults of Statnamic load testing into quasi-static load test results, because they would loose integrity in the process. What was recognized was that every Stat-namic test result was unique and that very small dif-ferences in the relative stiffness of two different foundations could be measured accurately. Much like the dynamic resistance of a driven pile, it is very useful even though there is no direct correlation to static resistance.

The Statnamic test has been described as applying

a controlled strain while monitoring corresponding deflection. When a test is performed, a predeter-mined load is applied and the resulting deflection is measured.

The first approach to analyzing failure was to look to the displacement curve and to analyze the rate of change of displacement, or velocity of the pile. Normalizing the load and plotting load vs. ve-locity was examined in an effort to pinpoint the load at which the velocity begins to increase. This only worked well when the foundation experienced a plunging failure, and it did not work well when the pile was in a cohesive material.

Statnamic test results were also evaluated with a

simple 2.5mm offset method, which was analogous to the Davisson failure criterion but much more con-servative. All three of these methods of determining the point of failure were far too subjective to be of any great value.

In January of 1993, while reviewing the results of

pile 7 at Texas A&M the author noticed that during the unloading of the test the velocity of the shaft reached zero at a load, which corresponded closely to the ultimate static resistance. The foundation be-gan to rebound as the load was further decreased. PDA users had observed the significance of the point of zero velocity in the 1970's and some at-tempts were made to make use of it. However, dur-ing pile driving the point of zero velocity at the pile head does not correspond to zero velocity anywhere else in the pile unless the pile is very short and rigid.

The authors observation provided both a practi-

cal means of determining a significant point on the static load displacement curve and also a means of estimating the damping coefficient directly from the test results rather than from a soil boring. This Un-loading Point Method (UPM) assumed that the damping was a constant, which was zero when the velocity was zero, and that the pile was behaving as an elastic body, which could be treated as a lumped

STN SLTDLT

DLTsignal matching

Nw > 12

UPM & stress wavecorrections

UPM, no stresswave corrections

Nw > 1000

Nw < 6

no yes

yes

yes

no

no

Static load displacement behaviour

pseudoSTN

Figure 8. Stress wave influences as function of wave number Nw



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mass and a spring. Subsequent research has concen-trated on testing these assumptions and determining the limit of their validity. The unloading point method has provided a very simple universal method of analysis and was first published at the 4

th Interna-

tional Conference on Stress Waves in 1992. The basic principles of the method have been presented in the Appendix.

The UPM method is based on the assumption that

stress wave phenomena can be neglected. The author studied the validity of the method with the stress wave program TNOWAVE (1996) by varying the pile length with constant load duration. To quantify the stress wave influence he assumed a wave num-ber constant Nw = D/L, in which D = c.T and T the duration of the load, c the stress wave velocity and L the pile length. In this way it was possible to indi-cate when stress wave phenomena could be neglect-ed and when they should be taken into account.

A valuable extension to the UPM method is the

Modified UPM (M-UPM) by Justason (1997). The method simply involves the averaging of the top and toe velocity and acceleration for calculating the iner-tia and damping. The method can be applied to any length of pile, but becomes more necessary as the pile becomes longer (low Nw numbers). The stand-ard UPM method assumes that pile top velocity and pile toe velocity are in the same range. The M-UPM method is particularly useful when the pile top and pile toe velocity are not in the same range (elastic pile, high toe resistance). Averaging the pile top and pile toe velocities and accelerations yields more ac-curate inertia and damping forces. The method yields the best results when used in conjunction with an embedded toe accelerometer.

Prof. Gray Mullins of the University of South

Florida made an additional improvement to the M-UPM method, the "Segmental Unloading Point" S-UPM. This method uses measured strain gage data to separate the pile into "segments" and perform an M-UPM on each segment. The data for each seg-ment are added together to produce a total "derived static" load-displacement for the top of the pile. The S-UPM can be applied to any pile, so long as the pile has strain gages distributed over the pile shaft. The first application was the Taipei Financial Center in Taiwan - 1999.

The S-UPM method is briefly described below.

The Segmental Unloading Point Method extends the applicability of M-UPM to long piles. All assump-tions of the Unloading Point Method remain valid. The Segmental Method assumes each segment of a pile behaves as a single degree of freedom system. The method requires embedded strain gauge data. A

measure of toe displacement is desirable. All results are based on measured quantities.

iiiiAEF

where Fi is the measured force at level i, i is the

measured strain at level i (typically an average of all strain gages at level i), Ei is the calculated (or as-sumed) elastic modulus at level i, and Ai is the calcu-lated (or assumed) area at level i

1i

1ii

1iiL

2uu

where ui is the calculated displacement at level i,

Li is the length of the pile segment between levels i and i+1

2

uu

dt

dv 1ii

i

where

iv is the first derivative with respect to time

of the average displacement for the pile segment be-tween levels i and i+1

dt

vda ii

where

ia is the first derivative with respect to

time of i

v The Unloading Point method is performed on

each pile segment using the following equation:

iiiii1iiamvcSFF

where Si is the equivalent static force for the

segment between Fi and Fi-1

Si represents the friction forces on the each pile segment, with the exception of the bottom pile seg-ment, which also has some component of end bear-ing. mi is the mass of the pile segment between i and i-1.

The cumulative derived static force at each level

can be calculated by the following equation:

n

1i

inSTATSF

where n is the pile level number, and FSTATn is the

cumulative derived static force at each level.



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The derived static load displacement curve can be drawn at each strain gage elevation using FSTATn and ui.

Each of the above variables represents an entire

data set measured over time. The S-UPM was first used for the Taipei Finan-

cial Center for 80m piles in 1999

5 THE HYDRAULIC CATCH MECHANISM

The foundation industry not only wanted to perform larger Statnamic tests but also more of them and at a higher frequency. Also in this case Patrick Berming-ham and design engineers came up with a creative solution. In 1995, the hydraulic catching mechanism was built to provide a means of testing, without us-ing the conventional gravel container, or gravel. This simple piece of equipment makes it possible to test up to ten individual piles and to perform multi-ple load-cycles. The catch mechanism provides the luxury of multiple load cycles within a matter of minutes, the ability to inspect the ignition circuit without disassembly, the benefit of single truck mo-bilization, and its avoids the environmental problems with gravel retrieval with testing over water.

Hydraulic catching systems eliminate the need for gravel and gravel structure since the upward moving reaction masses are caught at the top of their flight by four hydraulic actuators (or rams). These 3.2m stroke rams are activated by four low pressure (100 bar) nitrogen accumulators, which store compressed nitrogen gas over hydraulic oil. As the weight on the rams is released during a test, the compressed nitro-gen quickly expands to force hydraulic oil into the rams causing them to chase the reaction masses to the apex of their flight. The hydraulic oil is routed (in series) through one-way valves at the base of each ram, which restricts reverse flow, and thus the downward movement of the masses. Each of the four rams is independent of the others providing re-dundancy and safety. The masses remain at this po-sition until the user redirects the additional fluid in the rams back into the accumulators. At which time, a subsequent load cycle can be performed.

By transferring the initial weight of the masses to

the rams at the onset of the test it is possible to per-form Statnamic testing without a pre-load condition. Additionally, hydraulic catching systems have no minimum required jump-height for the silencer-reaction mass assembly, which is a concern for gravel catching systems. By removing this re-striction, low load tests can be performed with much greater than 5% reaction mass. Such tests can pro-duce long duration load pulses greater than 0.5 se-conds, thus reducing inertial and damping forces for large portions of the test.

Although the set-up time for a 4MN gravel or hy-

draulic catching systems is comparable, multiple cy-cles can be performed in a matter of minutes when using the latter. Further, the breakdown typically takes less time. In using gravel-catching systems, great care is exercised in the preparation of the igni-tion circuitry. An inadequate igniter connection could cost a project as much as a day of delay time. This of little concern when using the hydraulic catching system due to the ability to raise the entire stack of reaction masses with the hydraulic rams so as to access the fuel basket.

A substantial portion of all Statnamic testing costs stems from the mobilization of equipment. Typical-ly, a 4 MN test requires two tractor-trailers to ship the combined weight of the equipment and reaction masses (27,000 kg total) where only 20,000 kg is permitted per truck in the USA (30,000 kg in Eu-rope). The device can be equipped with two reaction mass options: (1) an entire set of six concrete-filled steel masses, which requires two trucks to ship, or (2) a set of six empty, structurally reinforced steel cans. The empty cans option allows single truck mo-bilization to distant sites with a total shipped mass of

Figure 9. Statnamic device with hydraulic catch mechanism (4 MN)



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19,000 kg. Once at the site the cans can be filled with sand, gravel, water or any combination to attain the required mass

3MN and 4MN hydraulic catching systems are

now in use in the United Kingdom, the USA and the Netherlands for 3MN and 4MN systems. In 2000 a mechanical catch mechanism will be constructed for a 16 MN device.

6 BATTER PILE TESTING

Drop hammers and dead weight static load tests are fully dependent on gravity. One of the big ad-vantages of Statnamic is its independence of gravity because generating the load it is based on inertia

forces. This means that the test can be performed in any direction: under batter, lateral and even allows to perform a tension test on a pile. In Figure 9 an ex-ample of the application of batter pile testing is pre-sented. It is almost impossible to perform static load test in this over water pile testing situation. The flight of the reaction mass is guided by a support beam

7 LATERAL LOAD TESTING

Lateral STN testing is becoming popular in the USA and was strongly encouraged by Barry Berko-witz of the FHWA. The first lateral test with a large device was at the Salt Lake City, Utah Airport in a research project with Kyle Rollins of Brigham Young University USA and a 14MN device was used. Mike Muchard and Don Robertson of Applied Foundation Testing perfected lateral load testing. They developed a "jig" for holding the piston and a "sled" for holding the silencer and masses.

A very significant job was for the Mississippi

DOT in 1998 to simulate a ship impact of 7.5MN by

the company AFT. Loads of up to 10 MN have now been applied in lateral load testing.

Major pioneering developments have been per-

formed by Dan Brown (1998) of Auburn University USA in the analysis of lateral Statnamic tests.

8 WATER REACTION MASS TESTING

A most significant development is the use of wa-ter as a reaction mass when testing piles over-water or near-water. By being able to mobilize the inertia of the ocean or a river, very large tests may be per-

Figure 11. Lateral load testing preparations for a 7.5MN test.

Figure 10. Over water Statnamic testing on a batter pile

Figure 12, Set up of Statnamic water reac-tion mass testing



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formed with testing equipment weighing only 1 % of

the test load. The necessary 5% or10% reaction mass would be provided by water confined within a vessel and submerged below the surface of the water. This weightless reaction mass makes it possible to per-form very large tests of longer duration than are practical today. The use of water reaction will also make it possible to drive piles underwater with a tool, which will be virtually weightless.

Statnamic testing using water reaction mass was first

done by Berminghammer in 1998 in Hamilton Har-

bour. These tests went to 600kN. The first field-

testing was performed for the Port of Lake Charles

in Louisiana in 1999 by Applied Foundation Testing

assisted by Berminghammer. The loads were up to

5 MN.

9 PILE DRIVING WITH WATER REACTION

Geert Jonker of IHC Foundation Equipment envi-

sioned the idea to extend the use the water reaction

mass into a pile-driving tool. Berminghammer, IHC and TNO are now working together to build an un-derwater Statnamic hammer, which will consist of a large inertial mass, made of water and a Statnamic tool capable producing multiple loading pulses. This tool will be used to push an anchor pile into the seabed and measure its capacity at the same time.

In the coming years, we will see driving small

onshore and offshore piles according to the Statnam-ic principle.

10 EVENTS

To share the experience among pile engineers and to improve the Statnamic test technology the first In-ternational Statnamic Seminar was held in Vancou-ver in 1995 with 25 papers and 54 participants. The Japanese research group on Rapid Pile Load Test Methods organized the Second International Stat-namic Seminar in 1998 with 48 papers and 132 par-ticipants. The third Statnamic seminar is planned in the Netherlands in 2002.

In March of 2000, the Japanese Geotechnical So-ciety (1998) published a standard for Method for Rapid Load Test of Single Piles

Figure 14. Water reaction mass testing

Figure 15. Artists impression of a water re-action pile-driving tool.

Figure 13. Water reaction mass containers



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An ASTM standard for Statnamic type pile test-ing is in progress.

11 RESEARCH AND DEVELOPMENTS

Companies and universities have accumulated up to date more than 700 case histories throughout the world. The total number of contract Statnamic tests worldwide has exceeded 1000, with testing now oc-curring at a frequency of more than one each day. The largest volume of testing to date has occurred in Malaysia, with the number of contract tests exceed-ing 300. Similar numbers of contract tests have now been performed in the United States. The UK and Japan are close behind in their numbers of tests.

An important contribution to the development of Statnamic was supplied by the Japanese Geotech-nical Society, which established the research group of Rapid Pile Load Test Methods in 1993. Professor Osamu Kusakabe of Tokyo Institute of Technology chaired the group. A strong promoter and initiator of Statnamic in Japan was Makoto Tsuzuki of Fugro Japan. The research group included 30 private insti-tutes and companies as members. The activities of the Research Group aimed at cataloging the existing knowledge about rapid load tests, examining the basic characteristics and the applicability of the test, and producing scientific interpretations of the Stat-namic test results.

The University of South Florida (1998) conduct-

ed over 150 Statnamic tests in conjunction with pri-vately and federally funded test programs. The tests programs have included: (1) axial load tests on piles and shafts in sands, clays, or rock-sockets, (2) lateral load tests on pile groups and shafts, and (3) plate load tests on sands and full-scale spread footings on sands and vibro-compacted soils (stone columns).

The application of Statnamic produces excellent

results in stiff and/or granular soils, although loading rate effects have to be taken into account. The influ-ence of soil viscosity alongside buildup of pore wa-ter pressure in fine grained soils requires further de-velopment of analysis tools and experience. (E.L.Hajuk et. al. 1998).

The soil viscosity shows up in two different

ways: - Creeping, this means continuing settlements

under constant pile load - Velocity dependent soil behavior Creeping phenomena cannot be determined with

Statnamic, dynamic load testing and in many cases not even with static load testing.

The velocity dependent soil behavior can be split

up in soil damping phenomena and strain rate de-pendency. Soil damping phenomena can be derived straightforward from a Statnamic test. Strain rate dependency for fine-grained soils is still subject to study, for example by the University of Sheffield UK (A.F.L. Hyde. Et all, 1998). Well-documented data from pile load test projects is becoming availa-ble to support the insight in strain rate effects (Holyman, et al., 2000).

12 CONCLUSIONS

The success of Statnamic stems for a significant part from the concepts and ideas generated by art-ist-engineers and engineer-artists.

According to Brandl (2000): an excellent engi-

neer requires not only a firm theoretical knowledge but also comprehensive experience as well as engi-neering feeling and intuition in equal parts. The au-thor would like to add: the ability to be creative and think in unconventional ways.

The success of Statnamic can be further explained

by the high degree of international cooperation and research, which has brought the technology to the forefront.

The Statnamic community originated from the

stress wave community and the author is sure that they will remain in close contact. Both have a com-mon interest in the research of dynamic phenomena of soils and the development of tools for the load testing of piles. The incorporation of the ideas of artist-engineers and engineer artists will guaran-tee more marvels in the development of pile testing applications and other fields of engineering.

13 REFERENCE:

Bermingham, P., Janes, M., An innovative ap-proach to load testing of high capacity piles, Pro-ceedings of the International Conference on Piling and Deep Foundations, London, 1989 . Middendorp, P. Bermingham, B Kuiper, Statnamic load testing of foundation piles. 4th International Conference on Stress Waves, The Hague, Balkema, 1992

Galluzi, P., Mechanical Marvels, Invention in the age of Leonardo, ISBN 88-09-20959-1, Instituto e Museo di Storia della Scienza, Florence, 1996.



www.profound.nl

Baudson, M., Panamarenko, Paris 1996

Fellenius, B., Welcome from the Chairman, First In-ternational Statnamic Seminar, Vancouver, 1995

Middendorp, P., Daniels, B., The Influence of Stress Wave Phenomena during Statnamic Load Testing, 5th International Conference on the Application of Stress-Wave Theory To Piles Orlando, Florida, 1996

Bermingham, P.D., Statnamic the first ten years, Proceedings of the 2

nd International Statnamic Sem-

inar, Tokyo, 1998

Hajduk, E.L., Paikowsky, S.G., Mullins, G., Lewis C., Ealy, C.D., Hourani. N.M., The behavior of piles in clay during Statnamic and different static load test procedures. Proceedings of the 2

nd International

Statnamic Seminar, Tokyo, 1998 Mullins, G., Garbin, E.J., Jr., Statnamic testing: University of South Florida Research, Proceedings of the 2

nd International Statnamic Seminar, Tokyo,

1998

Brandl, H., Civil and Geotechnical engineering in society Ethical aspects and future prospects, Pro-ceedings of the First International Conference on Geotechnical Engineering Education and Training, Sinaia, Romania, 2000

Brown, D.A., Statnamic lateral load response of two deep foundations, Proceedings of the 2

nd Interna-

tional Statnamic Seminar, Tokyo, 1998

Hyde A.F.L., Anderson W.E., Robinson S.A., Rate Effects in clay soil and their relevance to Statnamic pile testing, Proceedings of the 2

nd International

Statnamic Seminar, Tokyo, 1998

Justason, M. D.; Janes, M. C.; Middendorp, P.; Mul-

lins, A. G. Statnamic load testing using water as re-

action mass, The 6th International Conference on the

application of stress wave theory to piles, Sao Paulo,

Brazil 2000.

Holeyman, A., Maertens, J., Huybrechts, N.,

Legrand, C., Preparation of an international pile dy-

namic prediction event. The 6th International Con-

ference on the application of stress wave theory to

piles, Sao Paulo, Brazil 2000



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14 APPENDIX

STATNAMIC SIGNALS Load Fstn

Time Displacement u

Velocity v

Acceleration a

Funl

uunl

v = 0, t = tumax

aunl

Time

Time

Time

Fa

Displacement u

Load Fstn

Funl, uunl

Fstn(max)

Fstn

Fu

Load displacement diagrams

The Unloading Point Method (UPM)

Step I) Determination of static resistance from

unloading point

Assumption:

The long duration Statnamic load Fstn allows modelling of the pile as a

concentrated mass (M) and springs

Fstn = Statnamic force (measured and known)

u = displacement (measured and known)

v = du\dt = velocity (known)

a = d2u/dt2 = acceleration (known)

Fsoil = Fu + Fv

Fu = static resistance (unknown)

Fv = C.v = damping force (unknown)

C = damping factor (unknown)

Fa = M.a (known)

Equilibrium:

Fstn = Fsoil + Fa

Fstn = Fu + Fv + Fa

Fu = Fstn - C v - M.a

At maximum displacement (Unloading Point)

v = 0 u = maximum, t = tumax

Funl = Fstn(tumax) , aunl = a(tumax)

Fu(tumax) = Funl - M.aunl (known)

Static resistance Fu is known at uunl

Fu(tumax) , uunl is a static point

Step II) Construction of static load-displacement diagram

Assumption:

The soil is yielding over range Fstn(max) to Funl

So Fu = Funl

Over this range the following equation is valid

Fv = Fstn - Funl - Fa

with Fv = C.v

C = (Fstn - Funl - Fa) / v

Calculate mean damping factor Cmean for above range.

Now static resistance Fu can be calculated at all points

Fu = Fstn - Cmean .v - Fa

Draw static load-displacement diagram with Fu and u

Fstn

Fstn

Fsoil

Fa M

statnamic, the engineering of art, p. middendorp

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