Hans-Peter Günther

Welded Connections of High-Strength Steels For The Building Industry

The developments of steel structures aim at light and slender constructions. Therefore, high-strength steels with good welding characteristics and a high ductility, aside from higher strength, have been developed by the steel industry. With increasing strength of the steel, the loads which have to be transferred in the welded connections are also growing. In building constructions, fillet and partial penetration connections are commonly used. When using high-strength steels, it is very important to ensure strength, as well as sufficient ductility and toughness of these welded connections, in order to allow for the necessary redistribution of stresses and internal forces. The use of high-strength steels can bring significant savings in terms of material consumption, weight, transportation and fabrication costs. Beside the savings due to the reduced material consumption, advantages result from the smaller construction weight and a faster fabrication by reduction of the weld thickness. However, especially for high-strength steel grades S460 and S690, the benefit of saving of material cannot be used, dzue to the present restrictive design rules. Therefore, the aim of this research project, realized by four partners, was the development of appropriate and modern construction and design rules, as well as manufacturing principles, in order to achieve an economical use of high-strength fine grained steels. This paper presents the results of a research project, investigating the strength and ductility of fillet welded connections of high-strength steels S460 and S690, by means of experimental and numerical analyses. Experimental and numerical investigations of the load bearing capacity and safety against brittle fracture at lap joints with longitudinal fillet welds, cruciform joints with transverse fillet welds and butt joints with partial penetration double-V-groove welds of high-strength steels S460M/ML and S690Q/QL have been carried out. Numerical investigations in terms of welding simulation and measurements of residual stresses have been performed, in order to identify the local microstructure, hardness, residual stresses and strength in the weld profile. These results support the assessment of strength and ductility of welded connections. Based on the investigations, recommendations for the design of welded connections of high-strength steels, in terms of load bearing capacity and safety against brittle fracture, as well as manufacturing principles, were derived. The results of the research project thus contribute significantly to an optimized use of high-strength steel in welded constructions.

Rehabilitation of Welded Joints by Ultrasonic Impact Treatment (UIT)

Due to the increasing traffic and life loading fatigue becomes of high relevance in order to maintain the integrity of existing steel bridge structures. Poor construction details which used to be regarded as less important when applied e.g. to road bridges are nowadays often the starting point of fatigue cracks. Repair and strengthening of welded details are thus of great importance in order to extend the life time and safety of existing bridges. For welded details under fatigue loading one effective possibility to do this is the application of local post-weld treatment methods. This paper presents the application of a relatively new post-weld treatment method called “Ultrasonic Impact Treatment” (UIT). The paper summarizes the results obtained on a series of experimental fatigue tests where UIT has been applied in order to extend the life time of partially damaged non load carrying fillet welded joints.

9.2 – Investigations of Strength and Ductility of Welded High Strength Steel (HSS) Connections

The developments of steel structures aim at light and slender constructions. Therefore, high strength steels (HSS) with good welding characteristics and a high ductility in addition to higher strength have been developed by the steel industry. With increasing strength of the steel also the loads which have to be transferred in the welded connections, grow. In the building construction industry fillet and partial penetration connections are commonly used. When using HSS it is very important to ensure the strength as well as sufficient ductility of these welded connections. This paper presents results of a research project analysing the strength and ductility of welded high strength steel connections. Especially for S460 existing design rules show a conservative approach which now maybe revised based on experimental as well as numerical tests.

Strength and Ductility of Welded High Strength Steel (HSS) Connections in Bridges

High strength steels are more and more used in structural applications such as bridges or high-rise buildings. By increasing the strength of the steel the loads which have to be transferred in the welded connections increase in the same way. As high strength steels in general have a lower deformation capacity it is especially of importance for the connections to ensure beside the strength also sufficient ductility. This paper presents first results of a research project analysing the strength and ductility of welded high strength steel connections. Existing design rules according to Eurocode 3 are introduced and discussed showing that these rules are in many ways inadequate for high strength steel connections as they give e.g. very thick welds. First results of static strength tests on fillet welded connections together with numerical simulations are presented.