One Hundred Years of Structural Testing

The University of Sydney
Civil Engineering Graduates Association
Open Day - 30th May 1981
Address by Professor N.S. Trahair Challis Professor of Civil Engineering in The University of Sydney

The Opening of the J.W. Roderick Laboratory for Materials and Structures named by Sir Hermann Black Chancellor of The University of Sydney

Introduction

On Saturday, 30th May, 1981, at a Graduates Association Open Day, Sir Hermann Black, the Chancellor of the University of Sydney formally named the materials and structures laboratory of the Department of Civil Engineering as "The J. W. Roderick Laboratory for Materials and Structures".

The Graduates Association was addressed by Professor N. S. Trahair who traced the development of structural testing at the University of Sydney. Structural testing in the Department of Civil Engineering began nearly 100 years ago with the pioneer work of Warren from 1883 to 1925. Following a 26 year period of .further development and consolidation, guided by Miller, structural testing increased considerably with the appointment of Roderick in 1951, and the construction of the present laboratory in 1961. A new era of testing commenced with many additions of new testing equipment culminating in the installation of the new Dartec system in 1981.

Following this address, Emeritus Professor J. W. Roderick conducted the first test on the Dartec testing system. The capabilities of this system were then demonstrated by Associate Professor A. Abel.

Welcome by Professor N. S. Trahair

The Civil Engineering Structures Laboratory

On behalf of the graduates of the School of Civil Engineering, I would like to welcome the Chancellor of the University, Sir Hermann Black, to welcome Lady Black, to welcome our guest of honour Professor Roderick and Mrs. Roderick and especially to welcome Mrs. Davis. I am only to act as a master of ceremonies and to start things off, but before I do that I just want to say that I feel this is a particularly appropriate occasion - I know from my own background, first as an undergraduate student of Professor Roderick, later as a research student and finally as a member of staff carrying out structural research work and teaching work in this laboratory, what an appropriate occasion this one is. And so it is with much anticipation and great pleasure that I invite the Chancellor of the University, Sir Hermann Black, to perform the ceremony.

Naming of the J. W. Roderick Laboratory for Materials and Structures by Sir Hermann Black Chancellor of The University of Sydney

Professor Trahair, Guest of Honour Professor Roderick, Mrs. Roderick and ladies and gentlemen. This is a case when one has to be very careful to see that one's head stays in command of one's heart because there is unquestionably a unifying factor, a current of feeling, an emotional basis to this gathering. It's a current of feeling which I share with you, of deep respect for the man who is to be honoured by the unveiling of this plaque, which will be a commemoration of his work in terms of materials and structu res.

There are plenty of people who leave their mark and are respected. But when you leave a mark and there is not only respect but there is affection it is really a different thing; and hard-faced and hard-hearted as you may look as practising engineers, those hearts are and beneath those faces there are, I believe, quite normal human hearts. I interpret the presence of you all as people united in determination to do honour to J. W. Roderick; and I thank you for the honour of being the one who tries to put into words what you are feeling about him.

Now, I am not clairvoyant and I cannot read your minds because I did not have the privilege of being a student of his. Had I followed the early occupation of my grandfather on my father's side (he was an engineer, unfortunately in Victoria, but I say that simply because my mother, as she said rather unkindly, "dropped me" on this side of the Murray), had I followed my grandfather on my father's side I might well be standing there and amongst you as engineer to engineer, and paying a tribute to him.

But it would be impossible to, and it will in fact be impossible to write the history of this University - as it is being written and as it is being prepared now under the control of Professor Cable - to write it without reference to the central personalities who have in fact been involved at different points of time throughout the activities of this University. After all the University is not simply a series of impersonal activities between people who are on the staff, directed at those who are the birds of passage, namely, the students. It's not like that. It's a story of people and it's a story of contribution. It's a story of excellence in the contributions which flow from them into others and presumably you are on the receiving, or were on the receiving end of the excellent flow of services that are associated with him and for which you feel, I do not doubt, a sense of gratitude and debt.

So, we are paying honour to a stalwart figure. I once took the liberty, somewhat rudely, of calling him some years ago, a square block of a man. I will still continue to say block but not so square. But there it is, a square block of a man who has been one of the great engineers in this School. I think it is fitting therefore that the laboratory should in fact honour a person who is of that stature. But there is a certain symbolic quality about the fact that it is a laboratory which is to be the place where the plaque will commemorate his work. It is because the University is a place that has no end in terms of what its central function is.

There is no such thing as a full-stop in enquiry. There may be commas and semi-colons; but enquiry is an ever on-going stream of questioning, formulating new hypotheses, of shaping new theories, of testing them, finding them wanting, improving them and generalising them in some fashion or other. The on-going stream is the consequence of the fact that those who are at the forefront of enquiry now, stand aside as others take over the running, and stand in their place, contribute to that on-going expansion of knowledge which is the fruit of enquiry. Enquiry is the endless process of a university.

I once remember Lord Robbins, the great author of the Robbins' report on education, describe a university as a place of endless conversation and in a sense that is what it is, a constant dialogue between what we know and what in fact are the new things that are uncovered which make us query whether what we knew was quite as strictly formulated as it might be. And in order to continue that sort of questioning the laboratory is at the very centre of it. There you set up the test, there you conduct the enquiry, there you pose the question. And how lucky you are as engineers that you can have a laboratory in which you can set it up and ask the questions and read off the results.

It's different in the particular science in which. I waffle on. In economics you can't take a group of people and set them in some sort of laboratory condition and dangle before them a Grace Bros' shirt exactly lc less than you can get it at Waltons and say 'now watch how they react' because you just can't get that sort of controlled experiment. And it's therefore very difficult in economics. But happily you as engineers do have this sort of situation where you can structure an enquiry, where experimentally you can pose a question, where you can make some kind of model and run through it a series of enquiries at the level of a feed-in of different values and read off results. And I suggest that can in fact be done.

How nice it is that these days we live in a world in which those questions can be so quickly answered. And I have been immensely impressed by the speed with which the newer equipment permits the quicker answer, in terms of time, to be received after the question is posed. I was most struck when last week I had lunch, and very privileged indeed to have had lunch with the visiting President of IBM who had come to Australia from the United States to look over the operations of the firm here. He made (what was presumably made for people like myself who are complete ignoramuses) a very simple statement which indicated how quickly the answers to questions could be secured. He said that in time it takes to say the word 'computer', the one word 'computer', which, he said, might take exactly 1 second, IBM now has a machine which in that 1 second required to speak that one word, could carry out three million multiplications. Now at that I reeled back, not with surprise but with sheer joy, because if we have in fact secured that kind of command over the processes required to get answers then what is saved is time. And given that saved time one can in fact allocate it to still further enquiries, can press quicker on to the next stage of the experiment, to find out still more than could have been found out in the old days when it all had to be done by some simple slow rule of thumb.

So, in a sense, this is the tribute to J. W. Roderick ..... that this plaque commemorates the sort of person he was who taught you the disciplines of strict enquiry in the field of structures and materials. And this instrument, this laboratory is the instrument which will yield ever more rapidly, and, we hope, fully and excitingly all sorts of new results in the area to which it is devoted, namely materials and structures. I can think of no better thing that can be said of a man that when he retired from his task he had not in fact reached the point where he had said his last word. What does in fact confer honour on a man is that when he retired he has left, as his legacy, a series of interesting questions to be taken up and pursued by those who follow in his tracks. That's the real immortality. It is that you in fact pose questions or leave them in such a fashion that they are the paths down which your students subsequently wish to wander.

I don't think anything could be better done in honour of a man than that you say 'Sir, it is here where the mind is most active, in a laboratory; it is here where we will in fact carry on what you have taught us to the best of what you knew and now we will, with respect, take off from there. Maybe we will even qualify what you have taught us and modify it but certainly we will add to it'. And I am sure that he would want it so, that this would be the way in which this actual laboratory is operated.

So, in a sense, this is a moment where, at the point of time we now are at, looking back over the time that passed up to the moment of his retirement, we look back with affection and look back with indebtness for what he did in the past. At this moment, looking forward in a laboratory where this kind of basic intellectual enquiry takes place, this is the moment when the true scientist is in fact looking at his own immortality. This is what he is looking at... at those who will step forward into the as yet undiscovered areas of knowledge which this laboratory will make possible to discover.

Si Hermann Black Opening the Roderick Laboratory

So it marks those two things. It marks a point of time when you focus your gratitude on what he has done to bring us to this moment; but even more to say thank you for the fact that he has not foreclosed the future but opened it. That for a scholar is immortality. And that is why, generations after, it shall be so when there is no John Roderick, (but God forbid that Allah is thinking of a near time on that one and that he is long with us, as long as he carefully watches his diet.) Long may he be with us. At this moment of time you are, I am sure, standing there with affection, with emotion, and with a certain amount, I take it, of nostalgia, of thinking how it was. But there is this other dimension, there is tomorrow. There is the future which comes, there is the fact that tomorrow marches, its footsteps are, as it were, heard today.

At this moment, therefore, this plaque is, and I say this to J. W. Roderick, this plaque is in honour of what you have done for this University, and within it in this Engineering school, and again within it, in the area of Structures and Materials. Behind you stand those who are your disciples and in the future they will write their story as you have written it to this moment. A moment of nostalgia and a moment of great vision of the future to come. And the focus of it all, the J. W. Roderick Laboratory for Materials and Structures. And this plaque I now unveil in his honour.

Reply by Emeritus Professor J. W. Roderick

Mr. Chancellor, ladies and gentlemen:

First of all, I would like to thank you very much Sir Hermann for the kind and generous remarks you have made about me and my association with this laboratory. I would also like to take the opportunity to express my appreciation of the action of my colleagues in proposing that this laboratory should bear my name; and through you Mr. Chancellor, I would want to thank the Senate for having acceded to that request. And as regards this naming ceremony, I would like it to be thought of as a recognition of the efforts of all those who had some part in the creation and development of this laboratory.

I have some very pleasant recollections of those early days when we were planning this place; I remember Professor Harrison being much concerned with the design of the structure; I recall Professor Campbell-Allen giving a lot of thought to ways of redesigning some of our old equipment and to the layout of the new laboratory; and there were others who did many things to make it an exciting and satisfying time for us all.

In talking about that period, I take great pride in referring to the work of the laboratory and engineering general workshop staff who formed the construction team that built the strong floor. When we took over the building from the contractor, I would say that the most prominent feature in it was a large open space which looked for all the world like a great empty swimming pool. It was at this point that our construction team went to work; using what were then the biggest available steel joists, they fitted and welded up a very large grillage which when encased in concrete, formed a most effective strong floor. It is on this foundation that we have been able to test a range of structural units under a variety of loadings.

But moving on, our first real pleasure came when undergraduates began to use these facilities. It was a delight to watch the reactions of these young folk when they took their first classes in this new laboratory. But perhaps for me having closer contact with the graduate students, my recollections tend to focus on the camaraderie and enthusiasm which developed among them and which they succeeded in passing on to incoming students. Those were certainly stimulating days.

In talking to Professor Trahair and seeing what is going on today, it is good to know that the maintenance of a strong, effective materials and structures laboratory is still part of the policy of the School of Civil Engineering. Over the years this view has not always been generally acceptable to engineering schools around the world. In the early 1950's many were claiming that testing machines, loading equipment and the like were outmoded and that courses from then on should be much more concerned with engineering science and the use of computers in engineering.

Well time passed - there were indeed great developments in the computer field - but we still had engineering failures. I well recall the relevant remarks made by the U.S. Secretary for Air in talking about the troubles with the F111; he summed up by saying "we had gone too far out on paper". Gradually as other such incidents occurred, we came to realise that if you take the most accurate computer methods and associate them with wrong structure or wrong materials, the result can occasionally be disastrous. As you know the problems with the F111 were solved only after a long programme of fatigue testing.

Those events certainly had an effect on the planning of engineering schools in the United States. Many millions of dollars have been spent to ensure that both old and new civil engineering schools are now very well equipped with modern testing machines. So I reiterate that in looking around this laboratory and talking to Professor Trahair, I am delighted to see developments which will ensure that we maintain not only a laboratory -but a civil engineering school - of world standard.

Now let me say before concluding, that I want to express to all those working here at present and in the future, my very good wishes for the success of their activities, and the hope that they will find the experience as rewarding as I did. And finally may I, on behalf of my wife and myself, thank you very much indeed for making this an occasion which we will both remember with a great deal of pleasure and appreciation.


One Hundred Years of Structural Testing by N. S. Trahair, Professor of Civil Engineering The University of Sydney

The Warren Laboratory

Opening of the J W Roderick Structures Laboratory

Engineering was first established at an Australian university with the appointment of William Henry Warren in 1882. The Warren Laboratory (Fig. 1) can be said to have been initiated by the ordering of the Greenwood and Batley testing machine in 1884.

The Warren Laboratory

Figure 1

This horizontal testing machine has a load capacity of 45 tonne and can accommodate a maximum test length of 3m. It is primarily for tension tests, and is still occasionally used in this way today. It can also be used in compression and bending. Warren used it for teaching and for his extensive investigations into structural materials. Fig. 2 shows a small 50 mm x 50 mm x 0.6 m timber beam under test, and also a sector gauge used to measure the deflection of the beam.

Greenwood and Batley Machine

Figure 2

This test was one of a series to determine the effects of moisture content on the bending strength and stiffness of N.S.W. hardwoods.

Timber Beam Test in Buckton Machine

Figure 3

Larger 250 mm x 250 mm x 3 m timber beams were tested in the Buckton machine shown in Fig. 3. This is a vertical testing machine, with a capacity of 100 tonne and a maximum test length of 2.5 m. It can be used in tension, compression, and bending, and was installed in 1893. Like the Greenwood and Batley, its hydraulic jack was supplied by a water accumulator at pressures of up to 20 kPa.

In 1907 Warren was deciding how to equip a new Engineering building with gas plants, boilers, machine tools, motors, and electrical equipment. Also included in his budget of £6433 was an amount of E, 860 for an Amsler testing machine. This was a vertical compression testing machine, with a capacity of 450 tonnes and a maximum test length of 3 m. It came complete with its own oil pump and dynamometer, and an electric motor for moving the crosshead (Fig. 4).

Timber Test in Amsler Machine

Figure 4

The load measuring system used for this was simply based on measurements of the oil pressure acting on the hydraulic ram, and its accuracy was therefore dependent on the very low friction of the ram. It represented a significant departure from the systems of the earlier machines, in which the hydraulic force applied to one end of the test piece was balanced by a system of weights and levers reacting at the other end. The force acting was calculated from the weights and their lever arms. The Amsler enabled Warren to carry out a wide range of column tests, as well as to apply very large forces to short test pieces.

Warren continually added to the equipment in his laboratory, and by the early 1920's it must have been one of the most complete of its kind in the world. He used the equipment for teaching, and in his research on a very wide range of structural materials and components, including rivetted joints in steel ties, brick and cast iron columns, cement and reinforced concrete, and even composite steel and concrete compression members.

The results of many of his investigations were incorporated in his celebrated textbook "Engineering Construction", which occupied two volumes by the time of its third edition in 1921.

Warren Memorial Plaque

Figure 5

Warren retired in 1925 at the age of 73, and died suddenly in 1926. The plaque unveiled in his laboratory in 1926 is inscribed as follows (Fig. 5): "The Warren Laboratory for Testing of Materials. This tablet commemorates the life and work of William Henry Warren, LL.D., M. Inst. C.E., Dean of the Faculty and first Professor of Engineering in this university 1884-1925, and records the gratitude and affection of his students, appreciation of his work in the cause of engineering education, and his fife-long devotion to investigation of the properties and use of the materials employed by the engineer':

A Period of Consolidation

Warren was succeeded by William Aitken Miller who had joined him in 1913. Miller was a particularly gifted teacher, and concentrated most of his efforts in this work. General progress in the laboratory was hindered by the great depression 1929-33, by World War II, and by the Herculean labours of Miller and his staff in coping with the post-war influx of students.

Despite the years of financial neglect and stringency, the structural and materials research tradition established by Warren was maintained and continued. Miller was a great believer in the effectiveness of laboratory work, and developed a structural models laboratory, in which the force and moment distributions in flexible model trusses and frames were determined experimentally with Beggs deformeters and the like. There was also a photo-elastic laboratory for determining the stress distributions in complex elements. At the time of Miller's retirement in 1951, all of Warren's equipment was in excellent order, and a wide variety of work was able to be done, even though much ingenuity was usually required to adapt used (but not cast-off) hardware from the carefully husbanded treasure trove kept under lock and key.

The Roderick Laboratory

Jack William Roderick was appointed in 1951, and immediately set to establish in Sydney a programme of structural research into the plastic behaviour of steel structures which was a continuation of his own pioneering studies with Lord Baker at Leeds and Cambridge. Space was strictly limited in the Warren Laboratory, and so a Structures Annexe was established, with a small strong floor for testing beams and frames. This was powered by the pump and dynamometer of the big Amsler which had been replaced in 1954. A copy of the Cambridge testing frame (Fig. 6) was built for testing model steel beam-columns.

Sydney copy of Cambridge Testing Frame

Figure 6

By this time, some funds had become available, and already dial gauges (Fig. 7) could be used to measure deflections instead of the sectors (the dial gauges were limited in number, and a good case had to be made before Roderick would produce one from the bottom drawer of his desk).

Dial guages in a beam column test

Figure 7

In the late 1950's a great change came over the funding of universities, and Roderick was quick to seize the opportunity of new premises. The department moved to its present site in 1963, with the first stage, the materials and structures laboratory, being occupied in 1961. What then followed was an astounding transformation, with the construction of a large strong floor, the transfer of the equipment from the Warren Laboratory, and the installation of new testing machines, pumping units, and hydraulic jacks (Fig. 8).

The Roderick Laboratory

Figure 8

The strong floor 17 m x 13 m consists of a 675 mm deep welded grillage of steel beams encased in 1300 mm of concrete. This allowed the most dramatic extension of structural testing, which was previously limited to specimens which could fit into the testing machines. This strong floor enabled Roderick and his associates to carry out their extensive research into composite steel and concrete structures. Fig. 9 shows the test arrangement of a 1.8 m x 2.1 m span slab formed by casting concrete on a ribbed steel deck.

Composite Slab test on the strong floor

Figure 9

A central line load was provided by the jack which reacted against the H-frame connected to the strong floor. In effect, the strong floor takes the place of the lower cross-head of a testing machine.

Most of the materials and structures testing machines of Warren were transferred in 1962, the power systems of the Greenwood and Batley and the Buckton being converted from the water accumulator to oil pumps. Of these, the Amsler is in almost continuous use, both in commercial tests such as proof tests of bridge bearings, and in research and investigation work. Fig. 10 shows one of the stiffened plate panels fabricated for the Westgate Bridge being tested as part of the investigation made by Roderick after the collapse of that bridge in 1970,

Test of a Westgate Bridge Panel

Figure 10

The transformation of the laboratory was completed with the installation of 6 new testing machines. For the first time, a comprehensive range of equipment was available, covering a wide range of loads and testing conditions. Fig. 11 shows a small cylindrical steel shell being tested in axial compression.

Buckling test of a model steel cylinder

Figure 11

This was one of a series of model tests carried out to investigate qualitatively the buckling of steel silos and the strengthening effects of the grain contained within a silo.

The stress analysis and structural models laboratory was also transfered in 1962, but to separate accommodation. The work in this laboratory gradually decreased during the 1960's, although some research model studies were carried out on the buckling and post-buckling behaviour of beams (Fig. 12).

Buckling of a Steel Cantilever

Figure 12

In 1975, this laboratory became the C. A. Hawkins Computer Laboratory, and a PRIME computer provided by funds made available by the Graduates Association was installed (Fig. 13).

The Cecil A Hawkins Computer Laboratory

Figure 13

Subsequent Developments

From 1962, the materials and structures laboratory steadily developed, as Roderick and his staff were able to find funds to purchase new equipment, and to build special apparatus, such as the four "yooyo" machines used for low cycle fatigue studies. In 1963 the fatigue studies were boosted significantly by the installation of a Losenhausen universal dynamic testing machine, with a static capacity of 100 tonnes, and a dynamic capability of up to 1000 load cycles per minute. Fig. 14 shows a concrete beam with galvanised reinforcement being tested.

This is part of a series of tests to ascertain the effects of corrosive saltwater environments on the fatigue life of reinforced concrete structures, such as off-shore platforms.

Fatigue Test in Losenhausen

Figure 14

In 1964 and 1966 slow and fast cycling jacking equipment was added to the static jacking equipment. The N.S.W. Department of Main Roads made important grants for this equipment, which made possible the fatigue testing of composite steel and concrete beams such as those used in many medium span bridges. More recently, this equipment has been used to study the fatigue behaviour of welded T-joints between steel tubes (Fig. 15), such as those used in off-shore structures.

Fatigue Test of Welded Tubular Joint

Figure 15

Further additions in 1970 were two portable pumping units. Fig. 16 shows them being used in a lateral buckling test of a two span continuous steel beam on a strong floor. In such tests it is important to simulate gravity loading, in which the loads remain vertical even while the beam deflects laterally. This is done by using the sway mechanisms shown in Fig. 16.

Postable Pumps used in beam buckling test

Figure 16

The beginning of a new era of structural testing was heralded by the acquisition in 1971 of an Instron 25 tonne testing machine (Fig. 17). This machine consists of an extremely stiff frame (which deflects less than 1.5 mm under maximum load), with a moveable cross-head driven mechanically by hydraulically powered screws. Its most significant feature is a servo- loop control system, which enables the cross-head to be moved so as to produce a desired time variation of either the load, or the deflection, or the specimen strain. This was a significant advance over the hydraulic testing machines, in which flow control valves were adjusted manually to achieve desired load levels, or with some ingenuity and dexterity to achieve desired deflection values. The servo-loop system of the Instron enables this to be done automatically, and with precision. Fig. 17 shows the machine being used in a research project into the fatigue behaviour of aluminium alloys such as those used in the transport industry.

Instron Testing Machine

Figure 17

In Warren's Laboratory, typically only one test specimen response was measured, a moderate deflection by using sector gauges, or a small deflection using levers and mirrors. By the 1950's these cumbersome instruments were being replaced by dial gauges and electric resistance strain gauges. With the increase in testpiece size made possible in the 1960's by the strong floor came a corresponding increase in the complexity of the testpiece which may now consist of many components of several different types. The physical difficulty of making many measurements at each load level led to the purchase of a Compulog data acquisition system in 1973 (Fig. 18).

Compulog Data Acquisition Equipment

Figure 18

This system can make readings from up to 200 instruments in a matter of seconds, can store them in its own computer, or can output them onto paper tape through a fast punch. This allows subsequent analysis by the PRIME computer. The availability of the Compulog has led to a decrease in the use of mechanical dial gauges in favour of electric displacement transducers (Fig. 19) which convert deflections into electric signals which can be measured by the Compulog.

Fig. 19 shows these transducers being used in an investigation of a bridge made from prestressed concrete planks.

Displacement Transducers

Figure 19

While these events were taking place in the materials and structures laboratory, another area of structural testing was being developed in the hydraulics laboratory. Work on the response of structures to wind loading was initiated in 1962, and a large wind tunnel of 2.4 m x 1.8 m section was built in 1969. This wind tunnel can model the boundary layer effects of natural winds over various terrains, and has been used to study the response of a large number of structures, including the M LC building (Fig. 20), Westgate Bridge, and Centrepoint.

Wind Tunnel Test

Figure 20

Outside Tests

No survey of structural testing would be complete if it was confined to the laboratory. What follows is a brief sample which provides only an indication of the structural testing carried out on site by the department over the last decade.

Fig. 21 shows a full scale 18 m span steel industrial frame which was tested to failure.

Test of a Steel Portal Frame

Figure 21

The load capacity of such a frame is very dependent on the lateral bracing conditions in practice, and is often not easy to predict. The tests not only gave the manufacturer information directly relevant to his own product, but they stimulated further analytical and experimental research into the buckling of similar frames.

In 1972 there was considerable uncertainty in the profession following the spectacular collapse of a number of large box girder bridges. As a result of this a 3.0 m x 2.4 m x 50 m span steel box girder (Fig. 22) was proof loaded in the field prior to its incorporation into an overpass.

The girder behaved satisfactorily during the test, and no evidence was found of any incipient buckling or yielding.

Proof Test of a Steel Box Girder

Figure 22

More recently, there has been some uncertainty of the behaviour of axisymmetric containment structures, including those used for silos and tanks. Fig. 23 shows a 6.3 m diameter x 18.3 m high stainless steel fermentation tank which was internally pressurised and proof-tested prior to going into service.

The department instrumented the knuckle regions of this tank in order to monitor any possible buckling behaviour during the proof-test. No such behaviour was observed, and subsequent investigations have confirmed that the measured strains were close to those predicted by a conventional linear elastic analysis of the membrane and bending actions.

Proof Test of a Steel Fermentation tank

Figure 23

A partly constructed 5 storey office building is shown in Fig. 24, and 24 m x 17 m x 203 mm concrete slabs of which are prestressed.

The department carried out tests on one of these slabs in order to obtain realistic measurements of its creep and shrinkage which could be compared with commonly used predictions. Measurements were also made of the slab geometry, the tendon extensions and friction, and the concrete properties.

Five Storey Office Building Under Construction

Figure 24

The Dartec Testing System

From the middle 1970's, Roderick had sought finance for two substantial additions to the laboratory, one being a large capacity servo-loop testing machine to augment the 25 tonne Instron machine, and the other being to partially modify the existing jacking equipment to allow servo-control.

Early in 1979, a revised submission was made to the University seeking the finance for a testing system which could perform the tasks envisaged in the earlier requests. This revision was based on the concepts of a testing machine with a removable closed-loop jack (or actuator) which could be used on the strong floor in conjuction with another similar actuator, and of a central power system capable of a delivery to a number of points within the laboratory.

The revised submission was successful, and a grant of $225, 000 was made by the University. Subsequently, the N.S.W. Department of Main Roads made an additional grant of $80,000 available, which enabled the ordering of augmented power, distribution and control systems.

A Dartec testing system was ordered in 1979. This consisted of a 200 tonne testing frame (Fig. 25), two 200 tonne and one 25 tonne actuators, three static/dynamic and one static control systems, and a 350 litre/minute hydraulic pumping system.

The Dartec Testing Machine

Figure 25

This system was delivered in January, 1981, and installed and commissioned by Automation Industries Australia. The arrangement of the system is shown in Fig. 26.

Each actuator is double acting so that it can change smoothly from compression to tension loading. The actuator can be controlled to produce several desired time variations of either load, or displacement, or strain, with bumpless transfer from one mode to another. The static control provides for uniform damping with time, while the dynamic control provides for sine, square, or triangular cyclic loading. The control systems can also accept external time variations, such as those generated by an independent computer. Each control panel is equipped with a range of trips to ensure the safety of the equipment.

The pumping system will ensure a very good dynamic response from the 200 tonne actuators and will allow for a future static requirement of up to 1000 tonnes.

The testing frame includes hydraulic through zero specimen grips, a large base table for flexure tests, and can accommodate specimens longer than 2.5 m. The moveable cross-head which is mechanically clamped to the four columns, is unclamped and moved hydraulically.

The Dartec testing system is the most powerful ever installed in Australia. It has high load capacity and precision, a wide range of modes of operation (static, fatigue and dynamic) and control (load, displacement, strain). It can be used in materials research in the testing machine mode, or in structural testing in the machine or on the strong floor, where multiple loads can be applied. It will allow a very significant expansion in the structural testing work of the department.

Arrangement of Dartec Testing System

Figure 26

Conclusions

Almost one hundred years of structural testing at the University of Sydney have demonstrated both continuity and change. The three principal testing machines purchased by the far-sighted Warren are still in use despite their average age of more than 80 years. On the other hand, there have been dramatic changes in the structures being tested, and in the methods used to measure deflections and strains.

The building and equipping of the J. W. Roderick Laboratory for Materials and Structures has ensured that the department has maintained the leading position in structural testing established by Warren.

The new Dartec testing system will do much to maintain the excellence of the structural research and investigation work of the University of Sydney.