THE PLACE AND ROLE OF THE WELDING SPECIALIST IN THE DESIGN AND EXECUTION OF WELDED STEEL CONSTRUCTIONS

Dorin Radu 4 UDK: 621.791:624.014.2 DOI: 10.14415/konferencijaGFS2019.001 Summary: The emergence of new efficient materials, innovative welding processes, the high demands on the quality of the welded joints, while ensuring their safety in operation, outstanding aesthetic forms,the complexity of the new European welding standards, the pressure of the short execution times, lead to the need to emphasize the multidisciplinary character of the welding field, and a re-evaluation of the education in this direction. The paper presents some general aspects regarding the present problems in this direction, including the choice of the steel quality in welded steel structures.


INTRODUCTION
Welding is essential in many aspects of our everyday lives: infrastructure, economy, military, aerospace and arts. Welders build the world we live in. From cars to high rise office buildings, bridges, airplanes, none of it would be possible without welding. Practically riveted and bolted connections are used today, only in special cases. Seventy percent of all manufactured products are made with the skills of welders. Welders are not simple laborers, but technicians and scientists who are pushing the world into the future. Different studies found that the connection between welding and economics will continue to keep educated welders in high demand. Welding can be considered as an architectural art, creating the world in which we live, work and shop. Welding is a part of everything around us; without welding we wouldn"t be able to do the things we do. The emergence of new efficient materials, innovative welding processes, the high demands on the quality of the welded joints, while ensuring their safety in operation, the 7. МЕЂУНАРОДНА КОНФЕРЕНЦИЈА Савремена достигнућа у грађевинарству 23-24. април 2019. Суботица, СРБИЈА 14 | ЗБОРНИК РАДОВА МЕЂУНАРОДНЕ КОНФЕРЕНЦИЈЕ (2019) | outstanding aesthetic forms, the complexity of the new European welding standards, the pressure of the short execution times, lead to the need to emphasize the multidisciplinary character of the welding field, and of re-evaluation the education in this direction. The collaboration between the architect, the welding steel designer and the welding specialist is now essential. At the same time, in a global economy, a harmonization of the welding education becomes necessary. The aim of this paper is to establish general recommenddations in the field of design (including the choice of material) and execution of welded steel constructions as well as of the high-level education in welding.

THE BEGINNINGS
The industrial revolution, started in the XVIII century, led to the intensive increase of metal production and the improvement of the elaboration methods. The cast iron constructions, conceived as arch structurea, allowed telatively large spans, one of the first cast iron structures is the bridge in Coalbrookdale (1778), an arch with the span of L=31 m, still in use as pedestrian bridge.The cast iron structures, especially bridges had not given the expected results, yet as the use of this material needs complicated works and high costs. Additionally, the cast iron was brittle, having low tensile strength, producing many accidents, which made it, in time, to be forbidden in bridge construction. The appearance of the wrought steel at the end of the XVIII century (1784) and then of mild steels (Bessemer in 1856 and Thomas in 1880), leads to the construction of steel structures and bridges having more and more large spans and even records, such as the double railway bridges, Firth of Forth (1890) in Scotland with the two spans of 521 m and Quebec (1917), with the central span of 548 m. All the connection was riveted. The appearance and development of welding, as well as the economic advantages of welded connections, through the reduction of the fabrication costs and of the metallic material, imposed this new assembling technology for structures.In the beginning the same mild steel was used and the same joining types and constructive details as for riveted metallic bridges, without noting the necessity to obtain steels with special weldability characteristics and the use of specific constructive solutions.But the first practical results were discouraging. The series of accidents begun in 1938 when a span of the Rüdersdorf viaduct, one of the 50 welded plate girder bridges, built in the period 1931-1937 in Germany, collapsed. The cause of the accident was a crack in one of the lower flanges of the main girder.These events led to the suspension, in Germany, of welded bridge execution. Researches made in that period, continued after the II World War, led to the following conclusions:  fractures produced since material becomes brittle in the heat affected zone;  welding is not contra-indicated for bridges, but it is necessary to use a steel having optimum welding conditions;  welded constructions must be rigorous executed and controlled;  it is necessary to adopt suitable constructive details, to avoid stress concentrations;  necessity of some new quality weldable steels, like killed steels, fine grained steels, limiting the carbon content to maximum 0.2% and manganese to 0.75-1.70%, in addition with vanadium, nickel and aluminum.  After 1950, welding as a means of joining insteel constructions begin to become generalized. The experienceaccumulated in this field, but especially the exceptionally human capitalexisting in Timisoara, as well as a seriesof personal initiatives, led to the establishment in 1970 of the Institute for Welding and Testing of Materials. In the field of bridges, the first completely welded bridge with a large span, was erected in 1970 over the Danube (Fig. 4).

PRESENT TRENDS IN WELDED STEEL CONSTRUCTIONS
In the last two decades some an important progress was made in the field of welded steel constructions; in the following the most important aspects are analyzed. 1. New Steels → New Products →New Solutions (Fig. 5);   7. Gradually replacement of the classical S235 with S355 or a higher steel grade (Fig.11).

CONCLUSIONS
In the present context of the important European Infrastructure Projects the Eurocodes Standards, the necessity of safe and sustainable steel constructions (Fig. 12), the role of the Welding Specialist is decisive. A special attention must be paid to the education in the welding field.

Fig. 12 Sustainability of steel welded structures
Observation: This paper represents a short form of the presentation made during the Round Tablediscussion" Developments in welded steel constructions" held in Timisoara on 6.09.2018, organized by the Romanian Alliance of Technical Universities (ARUT),Politehnica University Timisoara (UPT), and the Romanian Welding Society ASR).A final Statement regarding the importance and necessity of the education in the welding field, was adopted.