Bernt Johansson, born in Stockholm in 1942. earned his MSc in Civil Engineering from the Royal Institute of Technology in 1961. He worked as a consultant engineer and continued his studies and presented his PhD thesis in 1976 on the stability of box-girder beams. In 1985 he was recruited to Luleå University of Technology to start research on steel structures. He initiated work with thin-walled structures, high strength steel and composite structures collaborating with industry. He played a pivotal role in the development of Swedish and European design codes. He supervised many master’s, licentiate, and PhD students. He passed away in 2017.

Structural fire design is exceedingly adopting the performance based approach. There are evidentadvantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on thereal performance, must accurately predict the beam behaviour in fire. The study presented here proposes one suchsimplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analyticalprocedure is validated through FE Analysis using FE models validated through test results. The study also attempts toestablish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviorof the restrained beam at catenary stage.

Structural fire design is exceedingly adopting the performance based approach. There are evident advantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on the real performance, must accurately predict the beam behaviour in fire. The study presented here proposes one such simplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analytical procedure is validated through FE Analysis using FE models validated through test results. The study also attempts to establish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviour of the restrained beam at catenary stage.

Prefabricated steel and concrete composite decks are an interesting option to improve competitiveness and sustainability of the composite structures. Longitudinal shear connection is usually established by grouped headed studs, but possible alternative solution is to use bolted shear connectors. Welded headed studs and bolts (grade 8.8) are experimentally examined in the push-out tests (four tests on each). The same arrangement and dimensions of shear connectors (16 mm diameter and 100 mm height above flange) are considered and their resistances and behaviour are compared. Experimental results showed that headed studs and bolted shear connectors have similar shear resistance, while headed studs are more ductile. FEA is performed by ABAQUS/Explicit solver with damage material models to get more insight into behaviour of the specimens. FEA shows rather good agreement with experimental results. Influence of the bolt to hole clearance on the behaviour of specimens with bolted shear connectors is analysed and discussed

The constant increase in the wind power production leads to the need of higher wind towers, which brings up some questions regarding the effectiveness of tubular towers and respective foundations. This work focuses on the comparative structural design, life cycle behaviour and costs of onshore concrete shallow foundations for tubular wind towers (WT) when steel micropiles are used to improve resistance of the soil–structure interface (hybrid foundation). Typical wind loading for Turbine Class II and moderate seismicity (.25 g peak ground acceleration) is used to design and analyse 18 WT foundation case studies. This allows the comparison between shallow and hybrid foundations designed for three different hub heights and respective turbine rated power (80 m/2 MW, 100 m/3.6 MW and 150 m/5 MW) and for three different tubular tower solutions (steel, concrete and hybrid steel–concrete). The possible benefits of the solution using steel grouted micropiles are discussed in terms of potential environmental and economic impacts using life cycle analysis. The use of micropiles reveals to be an interesting solution to improve common shallow WT foundations since it allows the reduction of the dimensions of the foundation leading to significant environmental and cost benefits.

The methods proposed by the design codes for single member design in fire situation assume that these members are isolated in their response. The real response of structural members such as beams is, however, more complex due to thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of structure at high temperature in a way which includes its interaction with its surroundings such as in a full-scale fire test and in numerical analysis. This paper focuses on the numerical investigation of steel beams, with a concrete slab and connected to concrete filled tubular (CFT) columns through reverse channel connections. The finite element software ABAQUS has been used in this study. The aim of the investigation is to study the behaviour of the composite steel-concrete beam exposed to increasing temperature in fire.

This paper presents results from experiments performed on cold-formed high strength steel circular and polygonal sections. The test specimens were conceived to provide necessary information for development of tubular towers for wind turbines. A total of 32 high strength steel specimens were tested under uniaxial compression. Various thicknesses, openings and geometric imperfections were studied. Sixteen specimens without opening and sixteen specimens with opening were tested under axial compression in order to investigate influences of opening on the resistances. Tensile tests of coupon specimens taken from flat part, circular part and corner part were used to investigate basic properties of high strength steel material S650 and to evaluate influence of corner on the material strength and ductility. Initial geometric imperfections of the specimens were determined by using a 3D laser scanning method. The coupon test results were used to calibrate the ductile damage material models for modelling of fracture. Results from the experiments are fully described in this paper

This paper is the second part of the study on the cold-formed high strength steel circular and polygonal sections intended to be used in tubular wind towers. Results from 32 numerical finite element analysis (FEA) models were compared with and calibrated against results of the tests on 32 corresponding specimens. The FEA results agreed well with the experimental results in terms of resistances and load-displacement curves. Further investigations on the numerical models were performed. Yield stress used in the FEA significantly affected the resistances of the numerical models. Using 0.2% proof stress leaded to higher resistance than the experimental results. Corners significantly influenced buckling behaviour in the polygonal section models. Analyses of an oval opening in the tubular specimens showed that peak stresses around the opening were considerably higher in the polygonal section models than in the circular section models. Finally, investigation of sensitivity to geometrical imperfections indicated that failure modes of numerical models with geometrical imperfections according to EC3 significantly differed from those of tested specimens and numerical models with geometrical imperfections obtained from the 3D scans.

The present paper addresses how the commonly used Hertz formulas for contact stresses underestimate the actual stresses seen in practice due to temperature differentials, misalignments and other contruction-related defects. First, two failure cases of Swedish bridge roller bearings are analyzed and discussed; then, a detailed finite element (FE) model is used to investigate the accuracy of the traditional roller bearing design rules in view of issues such as abutment and girder deformability, misalignment imperfections and material nonlinearity. The bearing capacity of the studied rollers as provided by the manufacturer is used as reference. A rigorous FE model that accurately models girder, roller assembly and abutment provides the necessary information for the assessment of the related contact stresses, which were traditionally calculated by means of the Hertz analytical formulas. Numerical results first establish that roller bearings develop contact stress concentrations at the outer edges of the cylindrical drums. Second, it is established that the contact stresses are very sensitive to misalignment imperfections between the bridge girder and the abutment. Last, it is shown that the roller bearings develop inelastic deformation at relatively low loads in relation to the design load. These reasons, combined with the unlikelihood for roller bearings to shake-down, constitute the basis of the observed roller bearing failures.