- Email: [email protected]
Martin Jensen: An appreciation
Journal of Wind Engineering and Industrial Aerodynamics, 41-44 (1992) 15-22
15
Elsevier
MARTIN JENSEN: AN APPRECIATION by A. G. Davenport I first corresponded with Martin Jensen on the subject of modelling the boundary layer in 1958 and met him later, at the first International Conference at Teddington in 1963. In 1964 he invited me to collaborate on the development of the Danish and Scandinavian Code on wind forces. This meeting laid the basis of our fiiendship. After this, in addition to the great pleasure of working together on projects, nay wife and I holidayed, toured, attended Conferences with Martin and Inger and visited their summer cottage in Sweden.
A little over six years ago, Martin Jensen received from the University of Western Ontario a Doctor of Science Honoris Causa. His citation referred to him as a "bridge builder", in recognition of his achievements both professionally as an engineer and also as a scholar, in buiiding b~idges between different fields of knowledge. His pioneer thesis on shelter from wind is a blidge between aerod:~namics and agliculture, and explores the influence of wind on plant growth and the aerodynamic protection provided by trees and hedges. "The Model Law for Phenomena in the Natural Wind" is a bridge between the effects of wind in full scale and their representation by models in a wind tunnel. 0167-6105/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
16 His study of the flight of locusts, written with Weis-Fogh, is a bridge between aerodynamics and zoology and has become the foundation of all later work on insect flight. His book, "Engineering around 1700", is a bridge between the construction methods of the past and present. In addition to these bridges of the mind, as a civil engineer, Martin built many actual bridges, his crowning contribution being to the construction of the Lillebaelt bridge between Fynen and Jutland. These are the some of Martin's bridges. Each was a significant accomplishment in its own right. There were others. He assisted Johanssen in the development of the yield line theory. He wrote a book, Aerodynamik, one of the first recognizable texts on what has now become wind-engineering; written in Danish it has received less attention outside Denmark than it deserved. He carried out a study of the Wind Climate of Denmark and worked with a small committee which wrote the innovative Danish and Scandinavian wind loading code.
ORIGINS Martin was born in the town of Horsens on the east coast of J u t l a n d on 10th of August 1914. Inger, his lifelong companion, wife and collaborator lived in the house next door. After finishing his schooling he went to DTH - The Danish Technical University in Copenhagen- to study Civil Engineering. At the DTl-l, Martin met Professor Nokkentved and after graduating worked with him as his assistant in the Wind l, aboratory. Nokkentved was a disciple and collabGrator of Irminger and in the early 1930's, the two of them wrote a pioneer two volume treatise on Wind Pressures on Buildings. Nokkentved died in 1945 and after the war Martin took over the work on shelter effect sponsored by the Danish Heath Society. In 1952 Martin published the English version of his treatise on shelter effect. For this he earned a doctorate from DTH in June 1954. To gather the data for this study on the aerodynamic influence of landscapes, Martin and Inger traversed two lines across Jutland by bicycle. This provided one of the first detailed studies of the large scale effects of terrain on the boundary layer. In 1959 Martin published "Aerodynamik i den Naturlige Vind" which was one of the first general texts on "wind engineeling" and combined his research on the model law, with information on pressure coefficients (mostly by other authors in uniform flow tests), as well as his work on shelter, drifting of snow and soil, snow
17 fences and the dispersion of smoke. The suggestion is made of using the dispersion of smoke plumes as a direct indication of the intensity of turbulence and the roughness of the ground. In the late 1950's Martin's productive collaboration with Niels Franck began. This resulted in the two volumes entitled "Model-Scale Tests in Turbulent Wind" covering the experiments carried out at the Wind Laboratory at the Danish Technical Highschool. Part I is concerned with "phenomena dependent on wind speed (shelter at houses - dispersal of smoke)" and was carried out between 1952 and 1957 and published in 1963. Part II is concerned with "phenomena dependent on the velocity pressure (wind loads on buildings)" and carried out between 1957 and 1960 and published in 1965. These two remarkable series of experiments were used extensively in the preparation of the Danish standard for wind loading. It is important to realise that much of the research he carried out was as an amateur in the true meaning of the word. He loved it and was not paid. Apart from his honorary degree, he had the rare distinction of having earned two doctorate degrees - from the University of Copenhagen and the Technical University of Denmark. In most of his work Martin had special collaborators who provided the support he needed. They included amongst others, Weis-Fogh, the brillia~t Cambridge professor of zoology, Niels Franck and Gunnar Jensen, both civil engineers at Monberg and Thorsen and his remarkable wife Inger. Henning Rasmussen, Inger's brother, who worked in the machine shop at DTH helped with the model making and experimental hardware. Martin shared with Inger a love and curiosity in archaeology and anthropology. They explored and travelled widely, often off the beaten track - to Greenland, on safari in Africa, to the Caucasus. In a round the world journey on Martin's retirement they visited three destinations: the Sydney Opera House, Rennell Island, a remote, unfrequented island in the Pacific where they lived several weeks as the guests of the native people, and London, Ontario. His breadth of knowledge made him sometimes a formidable person. He would speak his mind, for example, on the subject of unproductive committee meetings. Although he and Inger had none of their own, they enjoyed the company of children and with students he was always very approachable. His colleagues at Monberg and Thorsen recalled his contribution to the training of many junior engineers - "they could not wish for a more inspiring and creative supel-cisor..... He possessed a unique gift for identifying the heart of problems and was able to clarify and convey complex matters in a convincing and easy
18
manner ..... In Martin Jensen, the gift for rational thinking and application of scientific method was married to practical skill and legendary capability". Martin died on the 31st of May 1990 - only a few days after Kit Scruton. The wind engineering community within two weeks had suddenly lost two very significant contributors. He was survived by his wife Inger and his sister. The following selections from Martin's writing give an impression of his interests and knowledge, as well as the man himself. T H E M O D E L LAW
In 1958 Martin wrote "The model-law for phenomena in natural wind". From the viewpoint of wind engi'aeering, this was perhaps his most important contribution. While other researchers (Flaschbart, Bailey and Vincent for example) none stated the modelling requirements more succinctly or saw more clearly the significance of neglecting the correct modelling. The summary of the paper is as follows: "A great many technical circumstances depend on the wind in nature and cannot, or only with great difficulty, be analysed except through model tests. As examples may be mentioned the wind load on buildings and structures, contamination of the air from chinmeys, the various sheltering problems in agriculture and in living spaces between buildings. There is an unquestionable need of model tests, and as a matter of fact, a great many model tests have been ,arried out in the course of time within the said fields and similar fields in the aerodynamic laboratories. These investigations, however, are to some extent misleading, because the test procedure, especially the model-law, has been wrong. It may seem strange that within a vast research field incorrect model-laws have been applied, but the explanation is both simple and not very flattering: ; the model tests have practically never been checked by full-scale tests in nature. The natural wind is turbulent, and the phenomena dealt with in this paper take place in boundary layer of the wind, and, as should be emphasized, are highly dependent on the nature of this boundary layer. Unfortunately, however, almost all previous model tests have been carried out in wind-tunnels with as far as possible ;a smooth flow of air, and as for models of objects standing on the ground, it has moreover been t~ied earnestly to avoid the boundary layer of the wind-tunnel.
19 The correct model test with phenomena in the wind must be carried out in a turbulent boundary layer, and the model-law requires that this boundary layer be to scale as regards the velocity profile." WIND CLIMATE At the end of 1957 the Danish Wind Power Committee established three stations in Denmark for wind measurements which were overseen by Martin. This committee finished its work at the end of 1961 but the recording stations were continued by Martin and Niels Franck at their own expense until 1968. This resulted in a publication "The Climate of Strong Winds in Denmark". The Introduction describes the following: "The maximum wind velocity in Denmark cannot be stated. The problem of strong winds is statistical and statements must therefore be given by probabilities. The following example will clarify this. In accordance with meteorological standard, the wind velocities given are at a height of 10 m, but are a mean value over 3 to 4 seconds. In a year chosen at random, a place on the west coast of Jutland will be struck by about 18 "storms" with a maximum wind speed of more than 20 rrds, the strongest of them probably culminating in a speed of 30 ntis. In a decade, 180 storms of more than 20 ntis must be expected, the strongest of which probably reaching 37 ntis. In a century, 1,800 storms must be expected, with 42 ntis as the highest wind velocity". LOCUSTS The series of ten papers by Jensen and Weis-Fogh on the flight of locusts appeared in the Philosophical Transactions of the Royal Society in the mid 1950s. The introduction to Part III on the aerodynamics oflocusts flight contains the following: "A proper understanding of how locusts fly must be based upon knowledge of how the wings are moved. A desert locust was suspended from a balance and placed in an airstream so that it flew under nearly the same conditions as during natural forward flight. Four stroboscopic slow motion films were selected for measurement. The movement of the wings, i.e. their positions, velocities and accelerations, were then calculated in sufficient detail to show how these quantities vary with time during one complete wing stroke. The aerodynamic lift and drag of the entire natural wing were measured in a wind tunnel with the wing arranged in different positions relative to
20 the flow ..... It was found that the calculated vertical force, when averaged over an entire wing stroke, equalled the average reduction in body weight as mea$ored directly on the flight balance. Similarly, the average thrust of the wings corresponded to the drag of the bod:y. The analysis showed how the aerodynamic forces vary during the wing stroke". E N G I N E E R I N G A R O U N D 1700
This book was published in Danish and English in 1969 on the occasion of the anniversary of Monberg and Thors~m In the preface Jensen write: "It is almost thirty :~ears since, by chance, I came across Leupold's books. When I read ~hem, and in those days it mainly meant reading the illustrations, a strong world was revealed to me, because like most young graduate engineers, I had only vague notions about the past of my profession. What Leupold had not quite grasped, or had misunderstood ~itogether, was rather amusing, but the strange and interesting thing was the many techniques which that era had in common with ours. Since then I have studied a substantial art of the technical literature published between 1650 and 1750, and have read about how the authors accomplished their building operations with acumen and success and, once in a while; about the errors and bad luck of their colleagues. In this way I became conversant with the reasoning of the technologists of that period. A mistake evident in most modern treatises about ancient technology is that the authors much too often inadvertently misinterpret their predecessors due to contemporary insight. The purpose of this work is to given an account of the building techniques which were used about the year 1700, intelligible to a structural engineer born later than 1650. The pitfall of misusing 20th century physical and technical insight in the interpretation of former techniques should have been avoided here, as the work is compiled almost entirely from old texts and illustrations. During the period concerned, technology did, of course, devei,ap and this development is accounted for so far as this is considered to be consistent with the main purpose. A selection is made from the available literature, mainly to include items which are typical of that time and essential to an understanding of its technology, and also to include certain parts which appear interesting or exciting. However, the plinciple is only to include methods which might actually have been used in practice. This p~inciple excludes that
2! substantial part of the literature which was designed at the writing desk by authors who did not have any contact with engineering practice."
THE LILLEBAELT S U S P E N S I O N BRIDGE Martin had extensive experience in eugineering practice. In 1970, he wrote a short article describing the "Erection of the Steel Superstructure" in a collection of papers assembled by the Conslflting Engineers Ostenfeld and Jonson to mark the completion of the bridge. "Planning the fabrication and erection of the superstructure was commenced in J a n u a r y 1966. It was decided that every procedure during erection should be considered afresh. To some extent, of course, methods used on other bridges were studied, but it very frequently turned out, however, that other methods could be considered more advantageous. Partly for that reason and partly because it is normal practice at Monberg & Thorsen, an exceptional amount of work was put into the design of equipment, as well as the design and description of procedures. In addition, many experiments were carried out, both full-size and using models." INTERNAL P R E S S U R E S At the second International Conference on Wind Loading on Buildings and Structures, Martin gave the Keynote Address. He described the evolution of his work on wind loading, richly embroidered with anecdotes~ One of these concerned an argument he was having with Niels Franck on internal pressures due to windward openings. To prove his point, Martin secretly decided on a practical demonstration, described thus: "I am living in a fiat in a house in the western outskirts of Copenhagen, the house is 17 storeys high and my fiat is in the top. Figure 22 will show you my flat. FP in the centre of the apartment means four-poster, there my wife and I sleep with the doors D1 to the balcony B open. One night there was a gale from the west so strong that the variations in pressure really were painful to our ears so I was sent up to close the doors D 1, and then we slept peacefully. A few hours after midnight I awoke. From the creaking and groaning of the roofs timber construction I understood that the wind direction now was a little south of west and that the wind had increased to a full gale. I remembered the problem with the internal pressure, my surrender, and especially my secret condition. So I planned a full-scale expe~.~ment. On the door D1 there was an overpressure, by opening the doors D 1, D2 and D3 this overpressure could be brought to the
22 room north of D3. In the ceilingthere is a hatch H opening upwards to the room under the roof. With this pressure on the underside of the roof and the large suction on the upper side, the roof could possibly be lifted. I went up opened D1 and D2 and was just about to open D3 when m y wife was beside me: "What the hell are you doing?" I explained m y experiment in some detail. The answer was: "You fool. I have m y new car parked down there, will you immediately close the doors and come to bed". This done m y wife said: "And there might be somebody down there too". In your scientificwork you sometimes meet barriers that you cannot overstep.
II
I
m
fp
Figure 22 POSTSCRIPT
- At the Conference the following telegram was sent to Inger:
"The delegates to the Eighth I C W E meeting in London, Canada and representing the InternationalWind Enginee~-ingCommunity send you their best wishes and indicate their desire to establish an international award to support a student in wind engineering in recognitionof the contributions and example of Martin Jensen."
15
Elsevier
MARTIN JENSEN: AN APPRECIATION by A. G. Davenport I first corresponded with Martin Jensen on the subject of modelling the boundary layer in 1958 and met him later, at the first International Conference at Teddington in 1963. In 1964 he invited me to collaborate on the development of the Danish and Scandinavian Code on wind forces. This meeting laid the basis of our fiiendship. After this, in addition to the great pleasure of working together on projects, nay wife and I holidayed, toured, attended Conferences with Martin and Inger and visited their summer cottage in Sweden.
A little over six years ago, Martin Jensen received from the University of Western Ontario a Doctor of Science Honoris Causa. His citation referred to him as a "bridge builder", in recognition of his achievements both professionally as an engineer and also as a scholar, in buiiding b~idges between different fields of knowledge. His pioneer thesis on shelter from wind is a blidge between aerod:~namics and agliculture, and explores the influence of wind on plant growth and the aerodynamic protection provided by trees and hedges. "The Model Law for Phenomena in the Natural Wind" is a bridge between the effects of wind in full scale and their representation by models in a wind tunnel. 0167-6105/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.
16 His study of the flight of locusts, written with Weis-Fogh, is a bridge between aerodynamics and zoology and has become the foundation of all later work on insect flight. His book, "Engineering around 1700", is a bridge between the construction methods of the past and present. In addition to these bridges of the mind, as a civil engineer, Martin built many actual bridges, his crowning contribution being to the construction of the Lillebaelt bridge between Fynen and Jutland. These are the some of Martin's bridges. Each was a significant accomplishment in its own right. There were others. He assisted Johanssen in the development of the yield line theory. He wrote a book, Aerodynamik, one of the first recognizable texts on what has now become wind-engineering; written in Danish it has received less attention outside Denmark than it deserved. He carried out a study of the Wind Climate of Denmark and worked with a small committee which wrote the innovative Danish and Scandinavian wind loading code.
ORIGINS Martin was born in the town of Horsens on the east coast of J u t l a n d on 10th of August 1914. Inger, his lifelong companion, wife and collaborator lived in the house next door. After finishing his schooling he went to DTH - The Danish Technical University in Copenhagen- to study Civil Engineering. At the DTl-l, Martin met Professor Nokkentved and after graduating worked with him as his assistant in the Wind l, aboratory. Nokkentved was a disciple and collabGrator of Irminger and in the early 1930's, the two of them wrote a pioneer two volume treatise on Wind Pressures on Buildings. Nokkentved died in 1945 and after the war Martin took over the work on shelter effect sponsored by the Danish Heath Society. In 1952 Martin published the English version of his treatise on shelter effect. For this he earned a doctorate from DTH in June 1954. To gather the data for this study on the aerodynamic influence of landscapes, Martin and Inger traversed two lines across Jutland by bicycle. This provided one of the first detailed studies of the large scale effects of terrain on the boundary layer. In 1959 Martin published "Aerodynamik i den Naturlige Vind" which was one of the first general texts on "wind engineeling" and combined his research on the model law, with information on pressure coefficients (mostly by other authors in uniform flow tests), as well as his work on shelter, drifting of snow and soil, snow
17 fences and the dispersion of smoke. The suggestion is made of using the dispersion of smoke plumes as a direct indication of the intensity of turbulence and the roughness of the ground. In the late 1950's Martin's productive collaboration with Niels Franck began. This resulted in the two volumes entitled "Model-Scale Tests in Turbulent Wind" covering the experiments carried out at the Wind Laboratory at the Danish Technical Highschool. Part I is concerned with "phenomena dependent on wind speed (shelter at houses - dispersal of smoke)" and was carried out between 1952 and 1957 and published in 1963. Part II is concerned with "phenomena dependent on the velocity pressure (wind loads on buildings)" and carried out between 1957 and 1960 and published in 1965. These two remarkable series of experiments were used extensively in the preparation of the Danish standard for wind loading. It is important to realise that much of the research he carried out was as an amateur in the true meaning of the word. He loved it and was not paid. Apart from his honorary degree, he had the rare distinction of having earned two doctorate degrees - from the University of Copenhagen and the Technical University of Denmark. In most of his work Martin had special collaborators who provided the support he needed. They included amongst others, Weis-Fogh, the brillia~t Cambridge professor of zoology, Niels Franck and Gunnar Jensen, both civil engineers at Monberg and Thorsen and his remarkable wife Inger. Henning Rasmussen, Inger's brother, who worked in the machine shop at DTH helped with the model making and experimental hardware. Martin shared with Inger a love and curiosity in archaeology and anthropology. They explored and travelled widely, often off the beaten track - to Greenland, on safari in Africa, to the Caucasus. In a round the world journey on Martin's retirement they visited three destinations: the Sydney Opera House, Rennell Island, a remote, unfrequented island in the Pacific where they lived several weeks as the guests of the native people, and London, Ontario. His breadth of knowledge made him sometimes a formidable person. He would speak his mind, for example, on the subject of unproductive committee meetings. Although he and Inger had none of their own, they enjoyed the company of children and with students he was always very approachable. His colleagues at Monberg and Thorsen recalled his contribution to the training of many junior engineers - "they could not wish for a more inspiring and creative supel-cisor..... He possessed a unique gift for identifying the heart of problems and was able to clarify and convey complex matters in a convincing and easy
18
manner ..... In Martin Jensen, the gift for rational thinking and application of scientific method was married to practical skill and legendary capability". Martin died on the 31st of May 1990 - only a few days after Kit Scruton. The wind engineering community within two weeks had suddenly lost two very significant contributors. He was survived by his wife Inger and his sister. The following selections from Martin's writing give an impression of his interests and knowledge, as well as the man himself. T H E M O D E L LAW
In 1958 Martin wrote "The model-law for phenomena in natural wind". From the viewpoint of wind engi'aeering, this was perhaps his most important contribution. While other researchers (Flaschbart, Bailey and Vincent for example) none stated the modelling requirements more succinctly or saw more clearly the significance of neglecting the correct modelling. The summary of the paper is as follows: "A great many technical circumstances depend on the wind in nature and cannot, or only with great difficulty, be analysed except through model tests. As examples may be mentioned the wind load on buildings and structures, contamination of the air from chinmeys, the various sheltering problems in agriculture and in living spaces between buildings. There is an unquestionable need of model tests, and as a matter of fact, a great many model tests have been ,arried out in the course of time within the said fields and similar fields in the aerodynamic laboratories. These investigations, however, are to some extent misleading, because the test procedure, especially the model-law, has been wrong. It may seem strange that within a vast research field incorrect model-laws have been applied, but the explanation is both simple and not very flattering: ; the model tests have practically never been checked by full-scale tests in nature. The natural wind is turbulent, and the phenomena dealt with in this paper take place in boundary layer of the wind, and, as should be emphasized, are highly dependent on the nature of this boundary layer. Unfortunately, however, almost all previous model tests have been carried out in wind-tunnels with as far as possible ;a smooth flow of air, and as for models of objects standing on the ground, it has moreover been t~ied earnestly to avoid the boundary layer of the wind-tunnel.
19 The correct model test with phenomena in the wind must be carried out in a turbulent boundary layer, and the model-law requires that this boundary layer be to scale as regards the velocity profile." WIND CLIMATE At the end of 1957 the Danish Wind Power Committee established three stations in Denmark for wind measurements which were overseen by Martin. This committee finished its work at the end of 1961 but the recording stations were continued by Martin and Niels Franck at their own expense until 1968. This resulted in a publication "The Climate of Strong Winds in Denmark". The Introduction describes the following: "The maximum wind velocity in Denmark cannot be stated. The problem of strong winds is statistical and statements must therefore be given by probabilities. The following example will clarify this. In accordance with meteorological standard, the wind velocities given are at a height of 10 m, but are a mean value over 3 to 4 seconds. In a year chosen at random, a place on the west coast of Jutland will be struck by about 18 "storms" with a maximum wind speed of more than 20 rrds, the strongest of them probably culminating in a speed of 30 ntis. In a decade, 180 storms of more than 20 ntis must be expected, the strongest of which probably reaching 37 ntis. In a century, 1,800 storms must be expected, with 42 ntis as the highest wind velocity". LOCUSTS The series of ten papers by Jensen and Weis-Fogh on the flight of locusts appeared in the Philosophical Transactions of the Royal Society in the mid 1950s. The introduction to Part III on the aerodynamics oflocusts flight contains the following: "A proper understanding of how locusts fly must be based upon knowledge of how the wings are moved. A desert locust was suspended from a balance and placed in an airstream so that it flew under nearly the same conditions as during natural forward flight. Four stroboscopic slow motion films were selected for measurement. The movement of the wings, i.e. their positions, velocities and accelerations, were then calculated in sufficient detail to show how these quantities vary with time during one complete wing stroke. The aerodynamic lift and drag of the entire natural wing were measured in a wind tunnel with the wing arranged in different positions relative to
20 the flow ..... It was found that the calculated vertical force, when averaged over an entire wing stroke, equalled the average reduction in body weight as mea$ored directly on the flight balance. Similarly, the average thrust of the wings corresponded to the drag of the bod:y. The analysis showed how the aerodynamic forces vary during the wing stroke". E N G I N E E R I N G A R O U N D 1700
This book was published in Danish and English in 1969 on the occasion of the anniversary of Monberg and Thors~m In the preface Jensen write: "It is almost thirty :~ears since, by chance, I came across Leupold's books. When I read ~hem, and in those days it mainly meant reading the illustrations, a strong world was revealed to me, because like most young graduate engineers, I had only vague notions about the past of my profession. What Leupold had not quite grasped, or had misunderstood ~itogether, was rather amusing, but the strange and interesting thing was the many techniques which that era had in common with ours. Since then I have studied a substantial art of the technical literature published between 1650 and 1750, and have read about how the authors accomplished their building operations with acumen and success and, once in a while; about the errors and bad luck of their colleagues. In this way I became conversant with the reasoning of the technologists of that period. A mistake evident in most modern treatises about ancient technology is that the authors much too often inadvertently misinterpret their predecessors due to contemporary insight. The purpose of this work is to given an account of the building techniques which were used about the year 1700, intelligible to a structural engineer born later than 1650. The pitfall of misusing 20th century physical and technical insight in the interpretation of former techniques should have been avoided here, as the work is compiled almost entirely from old texts and illustrations. During the period concerned, technology did, of course, devei,ap and this development is accounted for so far as this is considered to be consistent with the main purpose. A selection is made from the available literature, mainly to include items which are typical of that time and essential to an understanding of its technology, and also to include certain parts which appear interesting or exciting. However, the plinciple is only to include methods which might actually have been used in practice. This p~inciple excludes that
2! substantial part of the literature which was designed at the writing desk by authors who did not have any contact with engineering practice."
THE LILLEBAELT S U S P E N S I O N BRIDGE Martin had extensive experience in eugineering practice. In 1970, he wrote a short article describing the "Erection of the Steel Superstructure" in a collection of papers assembled by the Conslflting Engineers Ostenfeld and Jonson to mark the completion of the bridge. "Planning the fabrication and erection of the superstructure was commenced in J a n u a r y 1966. It was decided that every procedure during erection should be considered afresh. To some extent, of course, methods used on other bridges were studied, but it very frequently turned out, however, that other methods could be considered more advantageous. Partly for that reason and partly because it is normal practice at Monberg & Thorsen, an exceptional amount of work was put into the design of equipment, as well as the design and description of procedures. In addition, many experiments were carried out, both full-size and using models." INTERNAL P R E S S U R E S At the second International Conference on Wind Loading on Buildings and Structures, Martin gave the Keynote Address. He described the evolution of his work on wind loading, richly embroidered with anecdotes~ One of these concerned an argument he was having with Niels Franck on internal pressures due to windward openings. To prove his point, Martin secretly decided on a practical demonstration, described thus: "I am living in a fiat in a house in the western outskirts of Copenhagen, the house is 17 storeys high and my fiat is in the top. Figure 22 will show you my flat. FP in the centre of the apartment means four-poster, there my wife and I sleep with the doors D1 to the balcony B open. One night there was a gale from the west so strong that the variations in pressure really were painful to our ears so I was sent up to close the doors D 1, and then we slept peacefully. A few hours after midnight I awoke. From the creaking and groaning of the roofs timber construction I understood that the wind direction now was a little south of west and that the wind had increased to a full gale. I remembered the problem with the internal pressure, my surrender, and especially my secret condition. So I planned a full-scale expe~.~ment. On the door D1 there was an overpressure, by opening the doors D 1, D2 and D3 this overpressure could be brought to the
22 room north of D3. In the ceilingthere is a hatch H opening upwards to the room under the roof. With this pressure on the underside of the roof and the large suction on the upper side, the roof could possibly be lifted. I went up opened D1 and D2 and was just about to open D3 when m y wife was beside me: "What the hell are you doing?" I explained m y experiment in some detail. The answer was: "You fool. I have m y new car parked down there, will you immediately close the doors and come to bed". This done m y wife said: "And there might be somebody down there too". In your scientificwork you sometimes meet barriers that you cannot overstep.
II
I
m
fp
Figure 22 POSTSCRIPT
- At the Conference the following telegram was sent to Inger:
"The delegates to the Eighth I C W E meeting in London, Canada and representing the InternationalWind Enginee~-ingCommunity send you their best wishes and indicate their desire to establish an international award to support a student in wind engineering in recognitionof the contributions and example of Martin Jensen."