Academician Nikola Hajdin was born on 4 April 1923 in Vrbovsko, Croatia. He is a Serb by nationality. He is a retired professor of the Faculty of Civil Engineering in Belgrade. He was graduated from this same Faculty in 1951 and received his doctoral degree at it in 1956. He was elected research fellow of the Faculty of Civil Engineering in 1958 and assistant professor in 1960, associate professor in 1961 and full professor in 1966. In addition to subjects at the main course of studies: structural mechanis ,strenght of materials plates and shells, he taught the theory of plasticity, non-linear elasticity and the theory of thin-walled members at post-graduate courses. He was elected corresponding member of the SANU (Serbian Academy of Sciences and Arts) in 1970, and full member in 1976. He was the Vice-president of the SANU from 1994 to 2003 and has been its President since 2003.
During his professional career, N. Hajdin has held a number of scientific and professional posts in different national and foreign societies, including the following: president of the Yugoslav Group of the International Association for Bridge and Structural Engineering (IABSE) and member of the Permanent Committee of that organization, president of the Yugoslav Committee of the International Union for Theoretical and Applied Mechanics, Dean of the Faculty of Civil Engineering in Belgrade, president of the Yugoslav Association of Structural Engineers.
He is a (foreign) member of the Slovenian Academy of Sciences and Arts, of the European Academy of Sciences, Art and Literature seated in Paris, of the European Academy of Sciences and Arts, headquartered in Salzburg. In the year 2000, he was elected honorary doctor of the National Technical University of Athens.
He is a member of the Greek Association for Scientific Research of Metal Structures, of the Scientific Committee of the Costruzioni Metaliche journal (Italy), of the Swiss Association for Steel Structures, of the International Association for Bridge and Structural Engineering (IABSE), of the Scientific Committee of the International Association for Steel Structures (Eurosteel); he is an honorary member of: the Yugoslav Society for Mechanics, the Yugoslav Structural Engineers Society and the Greek National Society for Theoretical and Applied Mechanics.
The scientific areas in which N. Hajdin has made a considerable contribution are: Numerical Methods in Theory of Elasticity and in Structural Mechanics, Theory of Thin-Walled Structures, Bridges, Dynamics of impact on civil engineering structures.
In 1954, he proposed and elaborated a method for numerical analysis of boundary value problems the Theory of elasticity, which has proved to be suitable for one and two dimensional elastic systems. The method is based on modern numerical analysis concept and computer applications. It has been widely applied in various technical branches. In contrast to some engineering methods, such as Marcus' method for slab calculations and the very well-known method for arch dam analysis, developed in the USA during the construction of large dams known as the "Trial Load Method", the method proposed by N. Hajdin was based on fundamental differential equations of the theory of elasticity applied to two-dimensional problems. By converting differential equations into integral ones along the adopted network lines and their approximate numerical solution, a system is obtained of linear equations providing the solution of the problem.
The method found broad application in different engineering branches, notably civil engineering structural design and later also in water management engineering, in the analysis of transportation vehicles, sound analysis and in some other problems of a similar mathematical nature. It was cited and used in the works of foreign authors, and in England also in a number of masters' and doctoral theses. In view of its wide-ranging application, the exact number of citation is difficult to ascertain. We can say that it was cited between 50 and 100 times in foreign scientific literature, not counting its citing in the practical applications (projects, at different conferences and similar), and several hundred times in domestic literature. Among the author's works in that field, of special value is "The Integral Equation Method for Solution of Boundary Value Problems of Structural Mechanics", published in the international journal "Numerical Methods in Engineering" (55 and 56).
The application of this procedure is particularly valuable in the calculation of hydro-engineering structures. Large arch dams, such as Grančarevo, Mratinje and Glažnja were analysed applying this method.
The second scientific field in the Structural mechanics to which Professor Hajdin rendered an exceptional contribution are thin-walled structures the properties of which render them usable in various engineering branches, such as civil engineering, mechanical engineering, shipbuilding, aeronautics, and others. N. Hajdin's works in this field, for the most part published abroad, are among the most advanced and most important contributions of their kind. They have been presented in a number of journals and reviews, cited and used in numerous works and publications by foreign and domestic scientists. Exceptionally valuable among them are two monographs: "Dünnwandige Stäbe", Bd. 1 and 2 (with Dr. C.F. Kollbrunner), published by the Springer Publishing House in 1972 and 1975 respectively. The monographs constitute a unic work in terms of content, with a series of contributions originally describing the author's area of interest spanning well over twenty years (17 and 19).
Being among the first papers dealing on a broad plane with this subject, which is very important in structural engineering due to the innovations in structural design stemming from the broad application of welding technology, works of this type elicited keen interest among engineers and designers, mainly in the area of steel structures.
In order to illustrate this research we should mention that, before the mentioned books came out, Professor Hajdin had published, together with Kollbrunner, some ten extensive publications with over 1500 pages in all, most of them in German. A number of these publications have been translated into English by the Institute of the "Cement and Concrete Institution" and circulated as an in-house paper in different research and professional institutions.
In his scientific pursuit in recent years, N. Hajdin has focused on non-linear dynamic problems of mechanics, specifically the study of the impact of means of transportation on civil engineering structures, such as the impact of trains or vessels. These works, most of which were published in Switzerland, were the result of, among other, the practical necessity to protect structures exposed to the possibility of impact by means of transportation, primarily in Switzerland, so that they were partly financed by state institutions concerned with this subject matter. On the basis of these papers published in journals, official recommendations were drawn up for bridge calculation, specifically that of bridge piers impact response.
Academician Hajdin organized a group of scientists and together with English and Czech research institutions (University College Cardiff at Cardiff and the Institute for Theoretical and Applied Mechanics of the Czech Academy of Sciences in Prague) embarked on broadly-based cooperation on studying the scientific problem known as patch loading. The cooperative result of this research effort which lasted several years were a number of papers, of which certainly the most important is: "A Contribution to the Analysis of the Behavior of Plate Girders Subjected to Patch Loading" with N. Marković, cited extensively and adopted as part of the British Steel Bridges Standards (135).
According to figures from journals available to us, N. Hajdin's scientific opus of about 200 works, approximately half of which have been published abroad in eminent journals or presented at important scientific conferences, has been cited over 250 times abroad and 500 times at home, while his designs, in particular the Sloboda bridge in Novi Sad, have been cited several hundred times.
Professor Hajdin is a world-renowned author of a large number of steel, concrete and composite structures.
Focusing on the structural mechanics and actual research problems in this branch of applied mechanics, Professor Hajdin devoted an entire chapter in his activity to composite concrete and steel structures, where these two materials jointly contribute to the system as a whole. A basic scientific problem which started to be examined seriously after the Second World War was the phenomenon of concrete creep and shrinkage which with time leads to a redistribution of stresses within a single system. This effort resulted in several studies which are listed in the bibliography. On the other hand, in order to test some of these results, N. Hajdin started designing and erecting originally conceived composite structures. For instance, he designed the Orašje bridge (4) across the River Sava where, in addition to the carriageway slab a concrete slab was used in the lower section of the main girder above the supports, for the first time in the world. Such a structural solution was introduced in Germany, the leader in this field, as a novelty, only some twenty years later. To this experimentation with composite structures we should add overbridges in Ljubljana displaying an original compositing method in the lower section throughout the lenght of the span (5, 6) as well as bridges in Macedonia (8) and on the Adriatic highway (7).
An area of particular importance in the domain of design are Hajdin's cable-stayed bridges which have been estimated as an exceptional achievement. Cable-stayed bridges made a shy appearance as a bridge-building novelty in the 1960's. Perceiving this novelty as something promising a revolutionary change, N. Hajdin immediately started theoretical studies of such structures and seized the very first opportunity, that being the railroad bridge over the River Sava in Belgrade (3), to put the system into practice. At a time when barely twenty bridges of this type had been built in the entire world, he was the first designer in the world to venture on designing this type of bridge for railroad traffic, even though the prevalent professional opinion worldwide was that such a relatively flexible system was inapplicable to railroad traffic. The bridge was completed in 1979 and, thanks to the novelties applied, manifested all its good properties.
After this feat, only a short while later, N. Hajdin designed the Sloboda bridge in Novi Sad, which, at the time, set a world record for cable-stayed bridges with the cables in the central plane (2). This bridge has been frequently cited in world literature, both before and after its collapse during the NATO aggression in 1999. It is being reconstructed and it will be fully in accordance with the original design.
In the series of bridges of this type, the bridge spanning the River Vistula in the Polish town of Plock (1), which was awarded first prize at an international competition, constitutes the crown of his opus. With its record span of 375 meters, it further develops the concept of the bridge executed in Novi Sad.
We should underline the fact that N. Hajdin was one of the pioneers in the adoption and verification of this system, which after a little over 40 years became the dominant system worldwide for large spans, with over a thousand bridges employing this system.
Focusing at the beginning of his career on the theory of arch dams which he later based on his original method of integral equations, Professor Hajdin actively contributed, in the capacity of consultant, to a large number of water management engineering structures. As his contribution to the building of arch dams he designed the Glažnja dam in Macedonia (10), one of the largest arch dams of its kind (third in height in the former Yugoslavia).
Some of his designs are given in the list of important projects.
As an expert of international renown, N. Hajdin was retained as consultant by a number of designing and construction companies of world repute, such as:
As a visiting professor he lectured on the subject of thin-walled members at the Swiss Federal Institute of Technology (ETH) in Zurich from 1971 to 1973, a visiting scientist of the Swiss Association for Steel Structures. He visited Switzerland many times, participating in research in the theory of thin-walled structures. In addition, he delivered a series of lectures at scientific conferences, at foreign universities, scientific and professional institutions, such as:
He is a member of a number of different scientific committees of international symposia and conferences.
As a professor teaching specialized scientific subjects, N.Hajdin has held numerous post-graduate lectures and courses at the Faculty of Natural Sciences and Mathematics in Belgrade, at the Faculty of Civil Engineering and of Mechanical Engineering in Skopje, at the Faculty of Civil Engineering in Zagreb and at the Faculty of Architecture, Civil Engineering and Geodesy in Ljubljana. He cooperated with the Structural Designers Society of Slovenia and the 3rd Class of the SAZU (Slovenian Academy of Sciences and Arts).
He either headed or was a member of commissions for 52 master's and 42 doctoral dissertations at his alma mater and for certain number of dissertations at different faculties throughout the former Yugoslavia, at the University of Athens and the University of Helsinki.
Following are the more important of the many awards he has received: The October Award of the City of Belgrade for 1959, the October Award of the City of Novi Sad 1981, the AVNOJ Award 1987, several awards at anonymous competitions for bridges in Yugoslavia, as well as the recent (1996) 1st prize at an anonymous competition for a bridge across the River Vistula in Poland.