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Steel circular tubular elements are among the most commonly used types of structural element in offshore structures. The objective of this paper is to perform a comparative analysis of design standards for offshore structures with a focus on the structural design of these elements. The intention is to reach a conclusion about the level of safety that offshore and construction standards provide regarding the design of tubular circular elements. To this end, the bearing capacity obtained with ISO 19902 and Eurocode 3 (which does not contain specific provisions for offshore structures) parts 1-1 and 1-6 will be compared in a broad parametric study. Subsequently, the accuracy and level of safety that ISO and EC3 assume are assessed through numerical analysis using the ABAQUS software. The performance of a set of steel circular tubular elements is evaluated under axial compression and hydrostatic pressure. Finally, the interaction between axial compression and hydrostatic pressure is also analysed.

This paper summarizes the work carried out in the context of an ongoing investigation that aims to understand and characterize the structural behaviour of thin-walled single-cell regular convex polygonal section (RCPS) tubes, such as those widely employed in the steel construction industry. In particular, the first-order and buckling (bifurcation) behaviours are addressed and it is shown that they
i. exhibit several peculiarities, stemming essentially from the cross-section rotational symmetry, and
ii. can be significantly influenced by distortion-type deformation.
iii. The analytical and numerical results reported in this paper are obtained using generalized beam theory (GBT) and its computationally efficient specialization for RCPS recently developed by the authors [1]. In particular, the unique modal decomposition features of GBT make it possible to
i) identify the most relevant cross-section deformation modes,
ii) draw valuable conclusions concerning the mechanics of the problem under consideration from the analysis of the (modal) solution, and
iii) develop analytical and semi-analytical formulae for problems of significant practical interest.

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Development of efficient design guidance for stainless steel structures (considering non-linear behaviour, strain hardening and allowing for moment redistribution in indeterminate structures) is crucial for the widespread use of this corrosion-resistant material. This paper presents an experimental programme involving ferritic stainless steel simply supported and continuous beams (RHS and SHS) and the assessment of existing cross-sectional classifications and different plastic design methods available in the literature for indeterminate stainless steel structures, not currently allowed in stainless steel standards. The analysis indicated that some cross-sectional classification limits seem to be too optimistic for ferritic stainless steels and further research is needed in order to extend plastic design to these grades.

The connection concept is a key point in the design of steel structures which affects fabrication, erection procedures and the final costs. Welding processes have been extensively used for tubular trussed girders by combining shop welding with bolted flange solutions to facilitate straightforward connection procedures during erection. The present research addresses the behaviour of innovative beam-to-column bolted connections for steel rectangular hollow sections (RHS) which combine simplicity in fabrication and erection, favourable aesthetics for the case of visible structures and structural effectiveness. Four cruciform prototypes were tested under a static non-reversible bending moment with different bolted conditions: i) non-friction and ii) friction connection. The experimental results show that the proposed geometry with friction connections is able to develop a rigid elastic moment-rotation response up to usual loading conditions.

The research into a specific type of unstiffened extended end-plate joint used to connect I-shaped beams to concrete-filled rectangular hollow section columns is presented in this paper. The main idea is to use long bolts passing through the column to connect the beam end-plates in order to...
1) avoid intermediate connecting elements (e.g. a reversed channel) or special bolts (e.g. blind bolts), which are sometimes used in practice, and
2) improve the resistance and stiffness of the joint when used in seismic-resistant frames.
Firstly, a test programme was performed within an RFCS European project entitled HSS-SERF “High-Strength Steel in Seismic-resistant Building Frames”, 2009-2013. The test programme included defining specimens subjected to significant bending moments (and shear) or shear only. Analytical models based on the component approach and aimed at predicting the joint response were then proposed; their validity is demonstrated through comparisons with the test results. Finally, the requirements of EN 1998-1-1 related to full-strength resistance for the proposed joint configuration are discussed, accounting for the actual positions of plastic hinges and the possible individual over-strength factors for each component.

The demand for the use of hollow section structures in construction has experienced great progress in Brazil, despite being widely used for a long time in Europe and developed countries. The release of a Brazilian Technical Standard specifically for the design of hollow sections confirms this trend, together with the need for increased dissemination and implementation of studies and research to enable a better understanding and development of this technology. This paper presents experimental and numerical evaluations of the influence of chord normal stresses on the behaviour of tubular T-joints. The experimental programme consisted of six tests applying compressive loads to the brace. These results were compared with the numerical results obtained from a finite element model simulation performed in ANSYS to extend the results to cases with tension forces on the brace. The results were compared with the design provisions in Eurocode 3, Brazilian standard NBR 16239:2013 and ISO 14346. A new equation for the case where compression loads are applied to the chord for n ≤ -0.5 is therefore proposed, providing better agreement with the experimental and numerical results

This paper presents the results of an experimental campaign in which the buckling resistance of 12 concrete-filled dual steel columns was ascertained. Whereas some papers in the literature describe investigations into concentrically loaded stub columns with such typology, no investigations of slender columns have been found to date. The tests presented in this paper are the preliminary results of an extensive experimental campaign (28 tests) that analysed the effects of two parameters: strength of concrete (normal- and ultrahigh-strength concrete) and the ratio between the thicknesses of the inner and outer steel tubes. A numerical model was also developed and validated, which helps further investigations. The buckling load of the specimens at room temperature is analysed in terms of the strength of the concrete and the appropriate distribution of the steel in the composite column. By maintaining the same total area of steel, two combinations were initially studied: “thick outer tube-thin inner tube” and “thin outer tube-thick inner tube”. Finally, a discussion about the Eurocode 4 simplified method for composite columns, applied to these innovative specimens, is presented and shows unreliable results. Therefore, further tests would be needed to assess accurately the Eurocode 4 simplified method.

A series of full-scale laboratory experiments was conducted to investigate the cyclic behaviour of an external diaphragm joint between a steel I-beam and a circular hollow section column. The joint incorporated two diaphragm plates (DPs) welded to the column's external wall and bolted to the flanges of the beam using tapered cover plates (TCPs). The joint was designed to limit yielding and plastic hinging of the TCPs while the other joint components remained elastic. This is necessary if the joint is to qualify for use in structures classified in the damage control structural performance range according to FEMA 356. Two parameters of the TCPs are investigated in this paper: steel grade and bolt preload force. The use of higher steel grades was found to impose undesirable higher strain demands on the beam and DPs and dissipate less energy than the joints with the lower grade. A controlled reduction in the bolt preload force allowed connection slippage to occur beyond the serviceability limit, created an additional energy dissipation fuse and allowed rotation of the plastic hinge region to exceed the 25 mrad required for medium ductility class structures.

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This paper deals with a proposal to revise the effective width terms in the brace shear criterion for overlap joints in rectangular hollow sections (RHS). The background to the design equations in ISO 14346 for the failure modes, brace effective width, chord M-N interaction and brace shear are described first. That is followed by the relation between overlap joints in circular hollow sections and those in rectangular hollow sections and those with an I- or H-section chord. Finally, it is shown that the effective width terms in the brace shear criterion can - in the case of 100 % overlap joints - be better related to the thickness of the overlapped brace. In the case of smaller overlaps, &lgr;ov, limit ≤ &lgr;ov ≤ 100 %, the effective width should also be related to the thickness of the overlapping brace, where &lgr;ov, limit depends on whether the hidden seam at the toe of the overlapped brace has been welded.

The resistance of compression members may be calculated by the design buckling resistance based on the reduction factor &ggr;, which depends on the slenderness, or by the cross-section resistance based on internal forces according to a second-order analysis taking into account equivalent initial bow imperfections as well. The second way is especially advantageous in the case of axial forces and bending. Values for equivalent initial bow imperfections are given in codes such as Eurocode 3 [5] or DIN 18800 [4]. For comparison, initial bow imperfections are derived here from the buckling curves for compression members with different cross-sections, buckling directions and steel grades based on different types of cross-sectional interaction. The results are discussed and commented with regard to the design of compression members. Furthermore, investigations are carried out for cases of axial compression and bending moments My or Mz. Data available from ultimate load calculations are used for comparison. The consequences for the assumed design verification according to second-order theory are discussed and a proposal is presented.

ZJA Zwarts & Jansma Architects have designed a new light rail departure station in The Hague, The Netherlands. The spatial roof structure of the station is made of rolled steel rectangular hollow sections arranged in two independent layers rigidly connected to each other. A glass envelope covering the roof structure matches the contours of the steel exactly. Since the diamond-shaped glass panes could only be attached to the outer layer of the steel grid, the panes (with edge lengths of approx. 1.30 m) are supported on two sides only. When optimizing the overall geometry, the double-curvature area at the nose of the roof structure became a special focus. Knippers Helbig Advanced Engineering has managed to minimize the deviation of each single glass pane from the single-curvature geometry to a maximum out-of-plane deformation of only 3 mm. Therefore, the project is a great example of how geometry development can influence structural design and enable new approaches.

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The design and construction of sustainable and durable bridges with low maintenance costs is one of the tasks of road and railway administrations of the European Countries. The structures must be safe, economical and need less maintenance during their service life. All these needs can be found in integral abutment bridges. This solution, which eliminates the bearings and expansion joints, leads to low construction and maintenance costs. Integral bridges also have good earthquake resistance. Bridges are vital structures in the transport infrastructure; it is a fact that, in the last decades, composite bridges have become a popular solution in many European countries as a cost-effective and aesthetic alternative to concrete bridges. Their competitiveness depends on several aspects, such as site conditions, local costs of materials and personnel and the contractor's experience. The main topics of this paper are: design of integral bridges, innovative composite dowels for shear transmission, construction of bridges in Romania, structural analysis of bridges and monitoring.