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Particularly efficient steel components can be designed by performing a plastic global analysis of a structure made of high-strength steel (HSS) as well. However, plastic design of HSS structures is not embodied in current standards, which is why a broad research study was carried out to address different aspects of the use of HSS for plastic design. This paper deals with verified numerical investigations of the rotation capacity of HSS I-girders considering realistic true stress-strain curves, local plastic instability and damage mechanics approaches to predict ductile crack initiation. Various influences on the rotation capacity of HSS beams were assessed by varying flange and web slenderness ratios, material characteristics, system dimensions, stiffness of lateral supports and loading conditions so that recommendations for the plastic design of HSS girders can be given. It is apparent that, apart from the slenderness of the flange and the material properties, the slenderness of the web is one of the main influencing characteristics. The results show that the plastic design of HSS structures is possible when limits for cross-section class 1 are more severe for HSS grades over S460 up to S690 compared with the current limits in EN 1993-1-1.

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ISO 14346 permits fillet welds in rectangular hollow section (RHS) joints to be designed either (i) to develop the capacity of the connected brace or (ii) to resist the actual load(s) in the brace (i.e. as “fit-for-purpose”). However, no methods for design according to approach (ii) are given in the ISO or any European standard. In this paper, data from 41 weld-critical tests on RHS gapped K, T, Y and X joints under brace axial load(s) are analysed to determine a reliable method for the design of fillet welds as “fit-for-purpose”. “Weld effective length” formulae are evaluated in conjunction with EN 1993-1-8 (directional and simplified methods) according to the standard procedure of EN 1990. A reliable method, based on ISO 14346, is proposed for calculating the design resistance of all-around fillet welds in RHS gapped K, T, Y and X joints. Updates to the minimum fillet weld throat thicknesses required to develop the capacity of a connected RHS brace are also discussed.

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Unprotected steel and steel structures exposed to the atmosphere inevitably corrode. For thin-gauged structures especially, corrosion is critical for stability. Although the reduction in thickness caused by corrosion is insignificant for some structures, in other structures corrosion is unacceptable. Therefore, corrosion protection is a crucial issue for steel structures and the steel industry. Over the last decades, many new corrosion protection systems and innovative steel products have been introduced onto the market. Corrosion protection for cold-formed structural steel elements has been standardized through the introduction of the EN 1090-4. This paper introduces the harmonized rules for the corrosion protection of loadbearing thin-gauged structures. The zinc-magnesium-aluminium (ZM) metal coating system developed in recent years is also dealt with.

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999-1-1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. Numerical investigations were conducted because a need for improvement was identified. This part 1 of the paper describes the individual steps of the revision and the modifications discussed, which include the introduction of longitudinally welded members. Before going into the numerical investigations in more detail, previous observations are presented regarding buckling classes and plateau lengths. In part 1 of the paper, explanations of the numerical investigations are limited to presenting the modelling of the geometry, the mechanical properties and the imperfections as well as their respective variation in the context of the parametric studies. The results of the numerical investigations and the proposed design approaches will be presented in detail in parts 2 and 3.

This paper investigates the effects of stiffeners on the compressive and flexural capacities of cold-formed steel channel members. Stiffeners are added on the web of the channel section to form a new section called SupaCee. This new section is shown to be more innovative and stable than the traditional channel section. The structural advantages of this new section are investigated by comparing the capacities of SupaCee and channel members under compression and bending. The capacities are determined by using the direct strength method (DSM) according to AS/NZS 4600:2018 with the support of THIN-WALL-2, a buckling analysis program. It was found that the stiffeners are effective for small section dimensions and thicknesses, but become ineffective for large section dimensions.

This paper describes an investigation into the cross-sectional behaviour of elliptical hollow section (EHS) columns made from ferritic and duplex stainless steel. The EHS is a relatively new structural shape with a number of favourable attributes including aesthetic appeal, high strength-to-weight ratio, good torsional resistance and excellent flexural strength. In recent years there have been significant developments in the analysis and understanding of these shapes, although most studies have focused on carbon steel EHS. The work so far is taken a step further here by considering some of the newer grades of stainless steel that are used in structural applications. A numerical model is developed and validated against test data from the literature and is then employed to generate structural performance data. Subsequently, parametric studies are performed to investigate the influence of individual parameters such as the material properties, aspect ratio and local slenderness of cross-sectional elements. The accuracy of existing design procedures is assessed by comparing the numerical data with the resistances obtained using Eurocode 3. It is shown that the cross-sectional slenderness limits given in Eurocode 3 for EHS members made from carbon steel can also be safely used for sections made from ferritic and duplex stainless steel.

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Physical Models: Their historical and current use in civil and building engineering design.

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As part of the AiF-FOSTA research project P1020 “Economical welded joints of high-strength steels”, extensive tests were carried out at the Institute of Steel and Timber Construction at the TU Dresden. Tested were lap joints, cruciform joints and butt joints of steels in grades S500 to S960. The picture shows the flat tensile test specimens made from butt joints with a thickness of 20 mm and a width of 35 mm in the weld area to be tested. Fully and partially penetrated butt welds were tested. In order to determine the strains in the course of the tests, strain measurements were carried out using photogrammetry in addition to inductive measurements. For this purpose, a stochastic pattern of graphite spray was applied to the test specimens and the high-frequency image recordings were digitally evaluated (s. article pp. 138-149. Foto: TU Dresden, Institute of Steel and Timber Construction).

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In the AiF-FOSTA research project P1020 [1], a new design model for welded joints was developed. In this context, a small scale test on flat tensile specimens was designed, with the help of which various influences on the strength and ductility of the welds were investigated. Furthermore, extensive tests were carried out on overlap joints, cruciform joints with double fillet welds as well as partially and fully penetrated butt joints. This was done to calibrate the weld construction factor &agr;w, which takes into account the influence of the type of joint on the load-bearing capacity. In the following article, after a short summary of the current state of research, the design model, and the results from the parameter studies on flat tensile tests are described in more detail in [2-4]. Subsequently, the test program on welded joints and the calibration of the weld construction factor &agr;w are presented. Finally, the results of the design model and the tests carried out are compared with test results from other research projects and the design model of prEN 1993-1-8 [5].

Resilience has many components, but two are of importance when structural systems are envisaged, i.e. the capacity to resist the hazard, or robustness, and the ability to recover from the hazard. So, the structure may sustain structural damage, but collapse should be avoided. Moreover, the damages are repairable, such that the initial functionality is recovered.
In terms of structural mechanics, a robust structure is associated with a good balance between stiffness, strength, and plastic deformation capacity. As a result, it is expected that alternative routes are available for redistributing the loads and prevent the progressive collapse in case of a local damage. The seismic design codes in force today aim at these objectives by applying the capacity design method and using relevant admissibility criteria. However, there are exceptional situations when the earthquakes are more powerful than expected, and even the structures correctly designed can be at risk. The situation can be worsened by cascading hazards, like fire or explosion. When safety margins are exceeded, partial or global collapse can be initiated. The reliability demands of building structures at high seismic risk need to be considered to increase the resilience. One such approach is based on the so-called Dual Steel-Dual Frame concept, which combines steel grades and structural systems to increase the capacity of response and reduce the consequences of extreme hazards.

In this study, an experimental program on welded hollow section joints fabricated from high-strength steel is presented. The experimental program tested a total of six T or Y cold-formed circular hollow section (CHS) joints under brace axial compression. One mild steel with a nominal yield stress of 355 MPa and two high-strength steels with nominal yield stresses of 460 and 650 MPa were included. The test results and existing test database were used to evaluate the relevant design provisions for high-strength steel joints. The material factor - used in the current standards to reduce the design resistance of high-strength steel tubular joints - was found to be adequate for CHS T/Y-joints with steel grades up to 700 MPa. The chord stress effect resulting from a particular test setup needs to be considered when evaluating the experimental joint strength. The experimental load-indentation relationships were analysed to appraise the behaviour of high-strength steel CHS T/Y-joints from the perspectives of ductility and serviceability. The ductility of high-strength steel T/Y-joints is slightly lower than that of mild steel joints. T/Y-joints show relatively lower ductility and serviceability performance compared to CHS X-joint counterparts that comprise identical members. Local strain distributions in tested T/Y-joints of different steel grades were analysed to identify the location and intensity of strain concentration. The possibility of fracture failure near the weld seam of the cold-formed chord member is discussed.

By using parametric modelling tools, designers can simulate a high number of design-variants with relatively low effort. Visual programming software's like Grasshopper significantly lowers the threshold for beginners to start building parametric models. This paper discusses how using Grasshopper as a parametric design tool can be applied by structural engineers to improve well-informed decision making, when designing a steel structure. Finally, worth mentioning further possibilities parametric design workflows can bring are discussed such as optimisation strategies, optimising sustainability and including structural connections in the parametric model.

Many steel rope systems are subjected to fluctuating tensile loads and therefore can fail due to fatigue. Available fatigue test data indicate that rope diameter, mean stress, socket type, lay angle and rope length influence the fatigue resistance. Most of the tests were terminated before full failure of the ropes. This paper shows that the test termination criterion, such as fracture of the first wire, fracture of 5 % of the wires or full rope fracture, has a large influence on the resulting fatigue resistance. A probabilistic analysis is carried out for a rope system in a bridge, demonstrating that the required structural reliability levels are met when considering full failure as the end-of-life criterion for ropes.

Many steel rope systems are subjected to fluctuating tensile loads and therefore can fail due to fatigue. There are indications that the fatigue resistance of full-locked coil ropes is somewhat lower than that of other types of rope. Fatigue test data on full-locked coil ropes have been collected, but they terminate at different conditions. A semi-empirical model is employed to extrapolate the test results to full failure of the rope. The resulting S-N curve is being adopted for the revision of European standard prEN 1993-1-11.

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Approach to the alpha ventus offshore wind farm. The support structures are exposed to extreme fatigue loads. © Leibniz University Hannover, Institute for Steel Construction (s. article p. 74 ff.).

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