In Eurocode 3, Part 1-1 [1] two methods are given for the design of beam-columns. They have been criticized for their complexity. Furthermore, internal plastic redistribution of stresses of class 3 cross-sections is not utilized in the code. These shortcomings were resolved in proposal for amended rules in [5], however, the procedures for beam-columns are still complicated and difficult to understand.
An approximate method for the design of beam-columns was proposed 1968 in [6] which was addressed in the Commentary to the Swedish regulations for steel structures [10] and used in Sweden since then [11]. It was accepted also in Eurocode 9 for aluminium [4], where it is especially convenient to allow for softening of the material at local transverse welds, see [9]. The method is here proposed to be included also in Eurocode 3.
In this paper the resistance of class 3 cross-sections is discussed and the unified method for beam-columns is presented. Four worked examples are presented, three of them on rather complicated structures, to show the capability to treat such structures as well.

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Steel-and-glass structures for buildings, railway stations and airports are currently representatives of modern infrastructure worldwide. The first two, characteristic of Japan, have been discussed in previous articles [1], [2]. In this paper the authors look at Japanese air terminals.

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The elegant free-form steel-and-glass canopy covers the atrium of the redevelopment of the “CasaShopping” luxury home furnishings centre in Rio de Janeiro, Brazil. The eye-catching sculptural shape of the canopy is inspired by the ocean waves of the nearby seaside of Barra di Tijuca. The “Carioca Wave” rises out of a pool at ground level and arches over the atrium to provide a link between the shops and the main entrance at the lower level. The complex geometry of the structure places high demands on construction. The high-precision node-beam system was prefabricated in Europe in order to allow fast and simple assembly and erection on site. The free-form steel-and-glass structure - one of the first of its kind in South America - was developed in a collaborative design-and-build project between architect Nir Sivan (Rome, Italy), special contractor se-austria (Schoerfling, Austria) and Knippers Helbig advanced engineering (Stuttgart, Germany).

Jinji Lake Mall, a 290,000 m² shopping and entertainment centre, will be centrepiece to a development of several super-high-rise buildings by the waterfront of Jinji Lake in Suzhou, China. Visible from the surrounding skyscrapers, the appearance of the “fifth façade” became of paramount importance. In response, the architectural design foresaw a continuous, 35,000 m² free-form glass roof to cover the four individual buildings of the mall ensemble.
schlaich bergermann and partner consulting engineers were tasked with the structural design of the roof whose shape was inspired by the wings of a phoenix. To alleviate excessive in-plane stresses in the roof, a rigid triangulated grid was discarded in favour of a more elastic quadrangular frame system, requiring the generation of a quad-dominant topology on the free-form surface. The complex interplay between base buildings and roof structure required that all analysis be done on a combined model including roof, tree columns and sub-structure.
Multi-resolution mesh modelling stood at the core of a generative work-flow which mathematically optimized for geometric and structural criteria in the same process. Furthermore, geometrically similar facets were grouped and subsequently assigned the same panel, reducing the unique panel count.

The linear architecture of the MAST (Manufacture Arts Experimentation Technology) multipurpose building in Bologna hides a complex combination of functions and spaces surrounding the core of the building and forms its raison d’être: the sublimation of innovation in manufacturing industry within the retrospective heritage of art and its projection in human memory. In this way, factors normally regarded as secondary to industrial activity become a central part of it and are acknowledged as its true roots and instinctive vision. The building acts as the vehicle for a declaration that there are no innovative ideas other than those arising from the interaction between memory and the capacity to project. The functional distribution traces a passage from emotive education (nursery) through formal teaching (classrooms) and the conservation of memory (museum and exhibition area) to listening (auditorium). Each function is acknowledged, not as a self-contained unit, but rather as a component part of the driving force of innovation, which propels a capacity for technological process that is anything but sterile. In such a setting, the steel structures are the very symbol of the transition from tradition to innovation [1].

Shorter product development cycles and compliance with exact process parameters during the production of high-strength heavy plate for heavy machine construction requires fast modelling of mechanical and technological material properties during the actual production process. To this end, the Heavy Plate Unit at ThyssenKrupp Steel Europe AG has used state-of-the-art calculation tools from collections of process data and test value databases. This report describes the step-by-step development of the underlying material models, their implementation in practical computer software and their practical application illustrated by some selected examples.

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The design of moment-resisting joints can often be a laborious task if performed by manual calculation. This leads to potential rising of unnecessary labour costs when industry approved design tool would otherwise suffice. Steel connection designers are charged with specifying joint components such as plates, welds and bolts required that have structural capacity to transmit the loads which the connection is exposed to. This said connection design and its components need to be economical with regards to cost. However, a balance needs to be reached between the over-design of the connection leading to excessive capacities, and the finite element design that provides the connection with just what it needs to resist such loads.
The aim of this paper is the description of an Excel based tool for the detailed design of bolted end plate connections between beams and columns in accordance to Eurocode 3. The design tool is practical, user friendly with minimum manual input and relatively transparent such that it provides the user with an easy step-by-step guide during the design process.

The Stuttgart School was the first movement to combine the style of and training in architecture, taught and supported at the Stuttgart College of Technology. The Stuttgart School of Building Design is losing visibility just as the profile of architects in society is rising. However, a thoroughgoing analysis of its particular qualities is overdue, especially in the context of creative construction engineering. For example, Bill Baker (*1953), a Structural and Civil Engineering Partner at Skidmore, Owings & Merrill LLP (SOM), Chicago, USA and winner of the 2009 Fritz Leonhardt prize, has described the creative approach as a key element in (civil engineering) training at the University of Stuttgart. Towards the end of the 20th century, the Stuttgart School of Building Design was greatly influenced by Jörg Schlaich (*17th October 1934), whose working, teaching and research methods also helped inspire the creative approach praised above.

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OpenSees is an open-source object-oriented software framework developed at UC Berkeley. The OpenSees framework has been recently extended to deal with structural behaviour under fire conditions. This paper presents the results of a numerical study, using OpenSees, of the progressive collapse of steel frames exposed to fire. After validating the capability of OpenSees against available analytical and experimental results of fire tests on steel members, a parametric study is carried out to find the progressive collapse mechanism of steel frames exposed to fire and corresponding influencing factors. The factors include load levels, lateral restraint, beam strength and fire scenarios. The catenary action of beams is considered by using a temperature-dependent corotational beam/column element. The results show that different progressive collapse mechanisms can happen due to the sequence of the buckling of columns. High load levels lead to the downward collapse of the whole structure compared with the lateral collapse for low load levels. The existing of lateral restraint causes the premature buckling of bottom columns which triggers the whole frame collapse. As the beam section increases, the collapse mechanism of steel frames changes from beam failure mode to column failure mode. The fire scenarios have significant effect on the collapse mode of steel frames. The work presented in this paper is a preliminary study of the progressive collapse of steel frames. Further work is underway to combine the influence of the effect of concrete floors. A simple design method is then expected to be proposed to investigate the robustness of steel structures against progressive collapse due to fire.

Seismic resistant building frames designed as dissipative structures, must allow for plastic deformations to develop in specific members, whose behaviour is expected to be predicted and controlled by proper calculation and detailing. Members designed to remain elastic during earthquake, such as columns, are characterized by high strength demands. Dual-steel structural systems, optimized according to a Performance Based Design (PBD) philosophy, in which High Strength Steel (HSS) is used in predominantly “elastic” members, while Mild Carbon Steel (MCS) is used in dissipative members, can be very reliable and cost efficient. Because present seismic design codes do not cover this specific configuration, an extensive European research project [1], HSS-SERF - High Strength Steel in Seismic Resistant Building Frames, was carried out with the aim to investigate and evaluate the seismic performance of dual-steel building frames. On this purpose, and based on a large numerical and experimental program, the following objectives have been focused into the project:
1. to find reliable structural typologies and joint/connection detailing for dual-steel building frames, (e. g. of HSS and MCS members), and to validate them by tests and advanced numerical simulations,
2. to develop design criteria and performance based design methodology for dual-steel structures using high strength steel,
3. to recommend relevant design parameters (i. e. behaviour factor q, overstrength factor Ω) to be implemented in further versions of the seismic design code, EN 1998-1 [1], in order to apply capacity design approach for dual-steel framing typologies,
4. to evaluate technical and economic benefit of dual-steel approach involving HSS.

While classic joining techniques in steel construction have undergone advancements, fundamental problems still remain. The utilisation of structural bonding can remedy the situation, but despite having many advantages, has not been able to establish itself in civil engineering and specifically steel construction. The reason for this are doubts by engineers, architects and contractors regarding the verifiability, durability and load bearing capacity of bonded steel constructions. In order to facilitate the use of the innovative joining technique in construction, it is necessary to process bonded joints close to standardisation.

In order to address global environmental issues, there is an urgent need for the building structure field to use as much timber as possible to contribute to reforestation, as well as to research and develop a building system that does not diminish the structure’s functionality and safety [1]. The building structure field is required to actively use this wood as timber, but the timber is too weak to use for large buildings. Research and development of an appropriate building system that can utilize such timber is necessary.
This study examines the possibility of developing a building system for a composite steel-timber structure utilizing the authors’ wealth of expertise in steel structure construction. Different types of composite steel-timber structure building systems are categorized, and their features are described. Furthermore, the individual types are evaluated for the performance requirements needed to develop a building system.

The paper shows experimental and numerical research into slender cross-section beams in case of fire. The topic is very important because little investigation has been made and little experimental data has been collected so far. In the framework of the RFCS project FIDESC4 - Fire Design of Steel Members with Welded or Hot-rolled Class 4 Cross-sections, several simple supported beams were tested at elevated temperature at the Czech Technical University in Prague.
Currently, Eurocode 3 contains a number of simple rules for design of slender Class 4 cross-sections which, based on recent numerical simulations, proved themselves to be over-conservative. Through refining these rules, material savings could be achieved, which would lead to greater competitiveness of the steel structures. This is being covered in existing research, but is not published in this paper, which is limited to lateral torsional buckling behaviour only.
Determination of the bending resistance for members subjected to lateral torsional buckling of Class 1-3 cross-sections at elevated temperature is based on the same principles as the design at room temperature, according to EC 3 part 1-1 [1]. However, it differs in using only one imperfection factor for all types of cross-sections. The informative Annex E of the standard (EC 3 part 1-2 [2]) recommends using the design formulas for slender (Class 4) sections as well. But there is a restriction of the critical temperature value and a different reduction of yield strength is used (0.2 % proof strength for Class 4 instead of 2.0 % proof strength for stockier Class 1-3 sections). For the non-uniform members (variable section height), a limited design procedure is given in EC 3 part 1-1 [1]. This is applicable for room temperature only. The possibility of using these rules for fire design is not yet confirmed.

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The paper addresses an experimental programme that is part of an ongoing investigation on the behaviour, strength and design of cold-formed steel lipped channel columns undergoing mode interaction involving local, distortional and global buckling. The 16 column specimens tested were selected to exhibit either (i) close local, distortional and critical buckling loads (PcrL ≍ PcrD ≍ PcrG) or (ii) PcrL ≍ PcrD (condition ensured via the cross-sectional dimensions) and PcrG up to around 20 % below or above that value (difference controlled via the column length). The test set-up, procedure and results are presented and discussed, and the failure load data obtained are used to explore the possibility of developing a design approach based on the direct strength method (DSM).

Cold-formed steel sections are widely used in many applications such as structural frames, scaffolding systems, purlins and storage racks. In particular, cold-formed steel portal frames can be an alternative to conventional hot-rolled steel portal frames for industrial, rural and residential low rise buildings. The advantages of using cold-formed steels include a higher strength-to-weight ratio and reduced material, erection and transportation costs.
Over the past two decades a number of researchers [1] to [3] have undertaken tests on cold-formed steel portal frames. The tests mainly focused on the behaviour of joints, and employed relatively stocky sections. Hence, they provided little insight into the effects of cross-sectional instability on the overall stability of the frame.
In this paper, three portal frame tests are described, the main purpose of which was to study the effect of cross-sectional instability on the two-dimensional sway failure of cold-formed steel. The tests demonstrated significant local and distortional buckling before reaching the ultimate load. Finite element models were calibrated against the tests. The calibrated models therefore can be used for a parametric study to investigate the significance of the additional second-order effects caused by local/distortional bucking. The paper details the tests and the numerical simulations.