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

Having in mind the topic of industrialised construction and the benefits of modular construction, sandwich panels are investigated to be utilised as load-bearing wall elements. To assess its full potential, the present paper tackles the linear elastic buckling response of axially loaded angle sandwich panels, by means of numerical and analytical calculations, as the upper bound of its load bearing capacity. The failures modes are obtained and framed for concentrically loaded angle panels with fixed and pin-ended supports. A parametric study of the angle panel comprising a series of finite element models is undertaken where responses are compared with analytical calculations based on the theory of sandwich panels. Boundaries for local and global buckling are identified and framed.

Flexural buckling is one of the main problems steel structures are faced with in ensuring an economic design. In Europe, the buckling resistance is calculated using an imperfection factor based on the section type, fabrication method, and steel grade. The current European design standards contain guidelines for the imperfection factor for sections made of steels with yield strength up to and including 700 MPa. However, the current design codes are based mainly on tests performed on steels with yield strength below 460 MPa. Therefore, the applicability of the methodology was reassessed. This paper reviewed the background documentation of the European flexural-buckling design methodology and discussed the current design practice described in the American National Standard. A total of 72 flexural-buckling experiments performed on cold-formed, hot-finished, and welded sections made of steel with yield strength in the range 690–960 MPa were collected and analyzed. Four models for estimating the resistance of high-strength steel struts subjected to pure compression were statistically evaluated based on the collected data. Finally, a recommendation for the estimation of flexural-buckling resistance of high-strength steel members is presented.

Regular convex polygon sections (RCPS) are commonly used as towers supporting transmission lines, stadium lightning and street lamps. Their use provides advantages in the bearing capacity and can simplify erection. Over the last 50 years experimental studies have been conducted to check the applicability of the plate theory to stocky polygonal columns. The paper presents the processed data gathered from compression tests found in the literature. Results from 70 specimens tested under pure compression were statistically analysed. Specimens with yield strength varying from 235 to 700 MPa and angles varying from 144 to 175.5 (5 to 40 sides) were investigated. The local non-dimensional slenderness was calculated using buckling lengths according to EN 1993-1-3 and EN 1993-1-5 with values ranging from 0.55 to 4.52. The objective of the paper was to compare the plate buckling resistance predictions to the experimental results. The paper concludes with a buckling width recommendation for evaluating the critical stress as calculated according to EN 1993-1-3 or EN 1993-1-5.

Stability in a structural mechanics context has posed a continuous problem throughout history for mathematicians, engineers and architects. Flexural buckling is one of the main problems steel structures are faced with in order to ensure an economic design. Different equations have been derived to estimate critical loads that could lead to collapse of compressed members. The buckling resistance of compressed struts are calculated in Europe using the European buckling curves. The method of calculating the resistance implies the use of a reduction factor based on 5 different buckling curves. These buckling curves differ based on type of cross-section, fabrication method and steel grade. The method has been generally accepted since it proved to be reliable and versatile. The current design codes are assigning the same relevant buckling curve to the sections made of steels with yield stress of above 460 MPa. This conservative approach is one of the reasons that discourages the use of high-strength steels in common structural applications, since the designer does not see a direct benefit from the additional steel strength. The first part of the paper briefly describes the origin of the European buckling curves. The second part presents two analytical models for calculating flexural buckling limit loads. Flexural buckling experiments performed on welded box and I-sections made of high-strength steel, with the yield stress in the range of 690-960MPa. The third part analyses the existing buckling experiments and statistically evaluates the models proposed for estimating the resistance of high-strength steel struts subjected to pure compression. The final part addresses the potential future research in the context of developing adequate flexural buckling curves for high strength steel (HSS) members.

Development of the wind energy industry continues to push the need for innovative solutions in terms of structural requirements. High-performance materials are thus needed to improve the efficiency of the structures and to ease the erection costs. The materials used for the towers have not improved significantly in the past years mainly because the design guidelines do not allow the efficient use of the high-strength steels. Lattice wind turbine towers could benefit from cost reductions if cold-formed high-strength steels would be used. Currently high-strength steel members have the same reductions factors for the relevant flexural buckling curve for cold-formed members regardless of the strength of steels. The paper discusses the approach towards the current European buckling curves and draws attention to potential limitations. The residual stresses present in rectangular hollow sections are discussed based on the method of fabrication. Different patterns of residual stresses are investigated by means of finite element simulations. The results indicate that the design codes slightly underestimate the flexural buckling resistance of high-strength steel members in the medium slenderness range.

The pursuit for cheaper energy is leading the current wind tower design to increased heights. Common wind turbine tower designs would generate unjustified costs for transportation and erection leading to inefficient use of materials. In order to reduce these costs, several simplified erection methods have been proposed. One of such is the hybrid lattice-tubular steel tower. For economic feasibility, built-up cold-formed polygonal cross-sections have been proposed for the lattice part. This article presents a numerical investigation of the failure modes of closed polygonal cross-sections. The first part contains a presentation of structural systems which incorporate elements composed of plates and cold-formed members. The evaluation of the polygonal sections is done by means of finite element analysis considering local and global geometrical imperfections and residual stresses generated in the fabrication procedure. A comparative study is performed between several finite element models to propose a corresponding European buckling curve for calculating the flexural buckling resistance. The results show that the design of polygonal sections can be done according to European buckling curves methodology.

Steel cylindrical shell structures are used in a large variety of civil engineering applications such as off- shore platforms, tanks, silos, wind turbine towers, etc. The local stability of such structures and their sensitivity to imperfections is a well-known problem. In current engineering practice the design method is based on the selection of an imperfection class for the shell and subsequently calculating a reduction factor,χ, to the resistance of the shell. One such methodology is supplied by the EN1993-1-6; special conditions are given to pressurized tubes subjected to meridional compression.

Past studies have focused on the stability of cylindrical shells with internal pressure. The stability problem of a long cylinder considering the internal pressure as a simple static load was addressed. Thus, the approaches considered the fluid as compressible.

The purpose of the present work is to investigate numerically the potential benefit of using an incompressible fluid fully enclosed in a circular cylindrical shell. The constraint imposed by the presence of the liquid in the interior of a shell will be referred to as “hydraulic constraint”. As liquids are nearly incompressible, the buckling of a liquid-filled shell has to satisfy the condition that the integral of all the displacements normal to the shell surface is equal to the volume variation of the contained liquid. The volume variation of the shell interior has to be equal to the dilation of the shell due to liquid pressure increments associated to the onset of geometrical instability. Additionally, the weight of the contained liquid causes additional circumferential tension in the cases of vertically placed cylinders.

The methodology followed is the numerical analysis of cylindrical shells by means of the ABAQUS Finite Element code and a comparison with the methods given in the Eurocode.

This paper introduces a novel joint based on a friction connection designed for column-splices. The jointwas developed within the scope of modular construction to improve the fast assembly of prefabricatedframes and to accommodate eventual misalignments. Gaps at the connection are considered on the jointhorizontal and vertical axis to accommodate misalignments whether they are rotations and/ordisplacements and so to allow for the easy fit of the columns. The efficiency of the joint resistance basedon different connection gaps subjected to uniform compression is assessed.