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Machine learning for design and analysis of steel frame halls The use of digital tools in design and construction processes increases efficiency, especially for recurring tasks and processes, such as the dimensioning of components or structures, which follow similar patterns. This paper develops an artificial intelligence (AI)‐based assistant for use in the pre‐design and design of steel frame halls as a prototypical co‐pilot. For this purpose, the necessary database of steel frame halls is first compiled from project archives of TRAGRAUM Partnerschaft Beratender Ingenieure mbB. This will be examined in the context of data analyses according to the decisive description parameters and similarities, so that finally suitable AI surrogate models for the prediction of the hall parameters are trained by means of regression analyses. Furthermore, an interface to the finite element program SOFiSTiK is implemented, which passes the predictions of the AI regarding the parameters of the steel frame halls to a parameterized input file and triggers the calculation and design. In the course of the calibration of the AI substitute models, in addition to the approximation qualities, possible safety margins to be provided are also discussed in the context of this article. This article shows that the prototypical co‐pilot for the preliminary design of steel frame halls could be successfully implemented. Furthermore the AI newly generated hall frames can be classified as stable with respect to the validation considerations. An outlook on future further developments of this approach as well as the transfer to other applications complete this paper. [ABSTRACT FROM AUTHOR]

Investigation of an engineering model for the assessment of the seismic behaviour of large mobile equipment For large mobile equipment in seismically active regions, seismic stability is an essential and often decisive design criterion. The seismic behaviour of such large equipment is usually characterised by complex nonlinear types of behaviour (uplift, tilting and rocking), which are difficult to compute and analyse in practice. In this paper, a highly simplified engineering model is presented or developed step by step, which should be able to represent basic features of the typical behaviour of large mobile equipment transverse to the rail under seismic excitation. The typical rocking motion of the equipment, as determined in previous analyses, is to be reflected in the simplified model. The engineering model will be designed in such a way that it is able to reproduce qualitative statements about uplift and rocking or tilting as a function of incisive model parameters and seismic excitation. The dissipation mechanisms of the model are presented and seismic tilting spectra are generated using different approaches. The suitability and applicability of these approaches for assessing uplift and rocking tendencies for large mobile equipment is reviewed using representative series of bucket wheel machines and stackers as examples. In addition, parameters are determined for quantitative application to further large mobile equipment and the delimitation criteria of qualitative and quantitative applicability are compiled. [ABSTRACT FROM AUTHOR]

Damage equivalence factors for deck slabs of steel railway bridges According to EN 1993‐2, the fatigue verification of railway bridges can be based on internal forces due to the standard load model 71. These internal forces are to be multiplied by a dynamic coefficient Φ2 and a damage equivalence factor λ. In this paper, factors λ1 allowing for the damage effect of traffic on quadrilaterally supported plates with torsionally flexible supports at the longitudinal edges as encountered in single‐track railway‐brides in a span range between 10.0 and 27.5 m are derived for three standard traffic situations. The required damage equivalence factors λ are obtained from the factors λ1, considering the annual traffic volume and the requested service life. [ABSTRACT FROM AUTHOR]

Unexpected fatigue cracks at main girders of a railway bridge – strain measurements under service and analyses based on fracture mechanics At a steel railway bridge, erected and taken into service in 1960, fatigue cracks were detected at some transverse stiffener to web connections at the lower flange of the main girder. These findings were surprising, because this specific connection detail was suggested in previous national design standards for fatigue. The paper presents the comprehensive strain measurements under service to show the local stress field at the critical detail within the web plate of the main girder, indicating the well‐known phenomenon of distortion‐induced fatigue, but with unexpectedly high resonance‐like bending stresses in the web. Based on fracture mechanics analyses, with implementation of the measured strain/stress data due to local and global effects at the transverse stiffener connection, as well as the measured material properties (fracture toughness and crack growth parameters) the remaining fatigue life was analysed. The positive results allow an unrestricted train operation in the future. It also turned out, that the mixed‐mode effects must be taken into account and considering only mode I at the crack tip may lead to unsafe results. [ABSTRACT FROM AUTHOR]

Design model for headed studs as shear connectors under additional tensile loading Headed studs are primarily subjected to shear when used as shear connectors in usual steel‐concrete composite structures. Consequently, initial design rules for shear connectors in composite structures did not address tensile forces directly. In case of horizontally lying headed studs embedded in a thin concrete slab such as in composite bridges, the headed studs may be subjected to tensile forces. For horizontally lying studs, current design rules consider a possible failure caused by a tensile load due to pull‐out by specifying geometric boundary conditions. As a consequence, relatively long shear connectors are required, which lead to uneconomical or impractical embedment lengths of the shear connectors. As meanwhile European code rules for fasteners under shear and tension (EN 1992‐4) have been developed, the upcoming Eurocode 4 refers to them for the design of shear connectors under combined tension and shear in composite structures. The fastening technology allows a direct design for tensile loading for different failure mechanisms, considering the influence of the reinforcement and concrete strength. Following this idea, this paper presents a design model for shear connectors in steel‐concrete composite structures under additional tensile loading based on experimental and numerical investigations considering recent developments in fastening technology. [ABSTRACT FROM AUTHOR]

Transversal load introduction into unstiffened girder webs – interaction with shear force and bending moment and implementation in new Eurocode version Transversal load introductions into unstiffened girder webs are often used economic solutions in building structures, not directly covered in the current Eurocode. Within this paper an engineering design model, developed at TU Graz, is evaluated for cases with additional high shear forces and bending moments acting at the girder. The resulting load carrying behaviour, in cases of interaction between Fz & Vz & My, is presented, based on comprehensive numerical studies, also for girders which are susceptible to web buckling. Finally, the modified design model is presented, which will be part of the new Eurocode version prEN 1993‐1‐1. In addition, a more general solution is shown, which could also be implemented in the Eurocode in form of a national Annex. [ABSTRACT FROM AUTHOR]

Penstocks with multiple thrust rings – accurate forces at thrust rings due to constraining effects and comparison with a simple design model Thrust rings are a component of penstocks and have to transfer the longitudinal forces of the steel pipe to the surrounding rock mass. Longitudinal forces occur primarily due the pressure loads at valves or at pipe covers. Within this paper, the realistic load bearing behaviour of different penstocks geometries with multiple thrust rings is presented, including constraining effects due to internal pressure and temperature. Results are shown with and without friction effects between steel pipe and surrounding concrete and are based on numerical FE analyses. In addition, a simple 1D beam model (design model), developed by the authors, is presented. The forces at the thrust rings are compared between both models. It is shown that also for different load combinations the simple 1D beam model gives accurate results for practical application. The FE study also shows, that always the load combinations with the constraining effects due to internal pressure and temperature must be analysed – a superposition of the results of the individual load cases leads to misleading results. [ABSTRACT FROM AUTHOR]

Abstract: Load bearing behaviour of combined steel pile walls under water pressure under the influence of positional imperfections. Increasing global trade leads to a significant expansion and strengthening of seaport facilities and thus to an increasing use of quay walls with combined steel pile walls. Horizontal loads, which mainly come from groundwater pressure, are forwarded by Z‐shaped intermediate piles via special connector profiles to I‐shaped king piles and then directed into the ground. The design of the intermediate piles is regulated in DIN EN 1993‐5. The test‐based method in provides the most accurate and thus most economic results. This paper shows how with this method water pressure resistances were derived for the HZ‐M/AZ‐system [2] in nominal position. However, fabrication influences often lead to deviations from the nominal position, which the intermediate piles have to compensate for. In this paper, the influence of a stretching of a sheet pile wall in the wall direction and thus an increase of the system width is examined. Firstly, the stretch itself is analysed and secondly, the load bearing behaviour of the stretched system is compared to that of the system in the nominal position. [ABSTRACT FROM AUTHOR]

Abstract: Dedicated to Prof. Dr.‐Ing. habil. Joachim Lindner on the occasion of his 80th birthday The aesthetical and structural advantages of tubular structural elements sustained the increase in their use in Brazil in last decades. The joints between tubular members remain a critical issue, with many studies indicating that further research is still needed, particularly for some geometries. In the past, some experiments on the influence of the chord stresses over the brace load capacity were published, but a definitive answer to this design issues was not reached. The first part of this paper presents an experimental evaluation centred on the effect of tension and compression chord stresses over RHS chord to SHS braces T‐joints. The results showed that compressive chord stresses could considerably reduce the joint resistance. In contrast, when tension chord stresses are applied the joint resistance increases but this is still not considered in the design codes. Still considering the tubular joints structural behaviour, there are cases where the ultimate resistance of the tubular joints may be enhanced by using flange plates as reinforcement, instead of replacing the chord or braces with stronger sections. Bearing this scenario in mind, the second part of this paper presents some experimental results of SHS T‐joints reinforced with flange plates to achieve a more economical design. The results showed that the joint resistance could be increased about 88 % using the reinforced plate with the same thickness of the chord profile. [ABSTRACT FROM AUTHOR]

Abstract: Limitations to the use of partial shear connection in composite beams with single flange steel beams and composite dowels – Part 1: Theoretical background, methodology and development of FE‐models. The plastic bending resistance design of composite beams with partial shear connection in EC4 is subject to several limitations of use. For instance, the shear connectors, usually shear studs, have to provide sufficient ductility (at least 6 mm deformation capacity) and the geometry of the steel beam is restricted to sections with either equal flanges or only slightly differing areas of top and bottom flange. Furthermore, EC 4 defines a minimum degree of partial shear connection. For composite members with single flange steel section and composite dowels, limitations to the use partial shear connection have not yet been researched. Because of remarkable differences regarding steel section geometry and deformation behaviour of the connectors a simple transfer of EC 4 rules is not possible and likely non‐conservative. In the first of two companion papers on that topic, the theoretical background and the methodology to investigate the limitations of use for partial shear connection are provided. Besides plastic design of several beams sections with partial shear connection, the paper presents the development of nonlinear, 3D FE‐models of composite beams with single flange steel beam and composite dowels, which are validated against experimental beam tests from the literature. [ABSTRACT FROM AUTHOR]

Abstract: Applying the theory of structural state of stress, this paper investigates the behaviour characteristics of concrete‐filled stainless steel tubular (CFSST) short columns during their experimental working process. First, the sum of the generalized strain energy density (GSED) values (Eij) of the short column at every load value (Fj) is normalized as Ej,norm to describe the structural state of stress. Then, the state of stress jump is identified by applying the Mann‐Kendall (M‐K) criterion to the Ej,norm‐Fj curve creatively, following the rule of quantitative change to qualitative change. The investigation reveals the general state of stress mutation characteristics of short columns at specific individual loads, leading to an update of the failure load. Furthermore, it is verified that the simulative working behaviour of short columns can also reflect the state of stress characteristics revealed through the investigation into the experimental data. Hence, we formulate the relationship between the failure loads of CFSST short columns using the simulative data, and then validate it through both experimental and simulative data. In total, this study explores a new way to reveal some unseen working characteristics of structures; hopefully, it will initiate similar research on various structures, and the results achieved will lead to more rational design codes. [ABSTRACT FROM AUTHOR]

Abstract: Large‐size HV‐bolt sets in ring‐flange connections are crucial structural members of wind turbine support structures, which are subjected to strong static as well as cyclic loads with considerable numbers of load cycles. Additionally to direct experimental investigations on the structural components themselves, analytical and numerical assessment methods of the bolts performance inside ring‐flanges are valuable engineering tools to gain knowledge about the structural behaviour and to support the development of appropriate design solutions. In this paper, probabilistic fatigue assessment, using Monte Carlo Simulation technique, is utilized to compute the failure probability and to investigate the influence of the scattering parameters on the fatigue performance of HV‐bolt sets in ring‐flange connections. Subsequently, an analytical fatigue calculation approach for large‐size bolts, based on the local strain‐life concept, is introduced. Results from two different methods for determination of required base material properties are compared. The calculations are validated on fatigue tests on HV‐bolt sets and results are discussed with regard to the evaluation of local loading conditions, damage assessment parameters and sensitivity to base material input. [ABSTRACT FROM AUTHOR]

Abstract: Investigations on the load bearing behavior of composite dowels positioned close to the free concrete surface. Composite dowels are an economic alternative to headed studs with various advantages. Modern concrete slabs are dimensioned increasingly thinner and often include several additional functions, for example air conditioning or thermal activation of concrete surfaces. For those applications composite dowels can be positioned horizontally in the concrete slab. Existing investigations on composite dowels describe different failure modes of composite structures such as splitting of the concrete, local compression of the concrete, pry‐out of a concrete cone or plasticizing of the steel teeth. At University of Kaiserslautern composite dowels with positions close to the free surface of the concrete slab were investigated experimentally by push‐out‐tests and on the basis of numerical simulations. In addition, the positive influence of a spiral reinforcement between the steel teeth was analyzed. Further primary and secondary failure mechanisms were observed for this specific position of the composite dowels. These investigations and a design approach will be presented within the paper. [ABSTRACT FROM AUTHOR]

Abstract: Equivalent initial imperfections for applying the partial internal forces method for flexural buckling about the weak axis. This paper compares design approaches for equivalent initial imperfections of steel members with hot‐rolled double symmetric I‐/H‐profiles subjected to buckling about the weak axis. In addition to the normative rules applied in Germany and Europe, design approaches for imperfections are also taken into account, which are currently discussed as part of the further development of Eurocode 3. A proposal using the partial internal forces method allows a consistent design for steel members taking into account the cross‐sectional failure as well as the flexural buckling about the strong and weak axis. The proposal leads to design results that agree well with the results of numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract: Dedicated to Prof. Dr.‐Ing. habil. Joachim Lindner on the occasion of his 80th birthday This paper reports the latest developments concerning the application of Generalised Beam Theory (GBT) to thin‐walled members with deformable cross‐section and whose undeformed axis is a circular arc, with no pre‐twist. Initially, the fundamental equations and relations are presented, leading to the first‐order equilibrium equations and associated boundary conditions, which can be written in terms of GBT modal matrices or stress resultants. Then, the procedure to obtain the cross‐section deformation modes is explained. Arbitrary (open, closed or ”mixed“) flat‐walled cross‐sections are covered, even though the kinematic constraints employed to subdivide the modes are much more complex than for prismatic members – in particular, the mode shapes become dependent on the curvature of the beam axis. Using a displacement‐based GBT finite element, a set of illustrative examples is presented, involving complex local‐distortional‐global deformation. These examples show that very accurate results are obtained with the proposed GBT formulation and that the modal solution provides in‐depth insight into the structural behaviour of naturally curved members. [ABSTRACT FROM AUTHOR]

Abstract: Introduction of the Direct Strength Method into the design of cold formed steel members according to EN 1993‐1‐3. Cold formed steel members have a varied area of applications in steel lightweight constructions but are subject to local and global instabilities due to compressive and bending stress. The design method of the European Standard EN 1993‐1‐3 is based on the Method of Effective Widths covering local and distortional buckling. Unfortunately, an EN 1993‐1‐3 design is time‐consuming and prone to errors, furthermore the results are often conservative. This paper is going to introduce a new, practical design method for cold‐formed steel sections that combines the established European regulations of global instabilities with the Direct Strength Method (DSM) described in the North American standard AISI Standard 100 regarding local stability analysis. Based on comparative studies of mono‐symmetric cross‐sections it is possible to demonstrate that this new method offers a great potential of improving the design of cold‐formed sections, additionally improves the economic efficiency of lightweight steel sections. More theoretical and experimental investigations are needed, deeper leading questions are to answer, until this method is able to supplement the European standard. [ABSTRACT FROM AUTHOR]

Abstract: Trough girders are widely accepted in engineering on account of lowing construction depth and protection against traffic noise pollution, but most of them are used for simple‐supported girder bridges with a span of generally less than 30 m. On the railway line of Nanjing–Qidong in China a new railway bridge will be built which has a span of over 64 m but a construction depth of less than 2.4 m on which Shanghai–Nantong railway line is also passed, so the type of concrete‐filled steel tube tied‐arch bridge with trough girder was chosen. For such a new structure hardly used in engineering, there are no research results yet available about mechanical properties of the structure. This paper therefore makes for the bridge an experimental model of 1:4 geometric scale in order to test mechanical properties under operation load, cracking load, and ultimate load such as cracking diagram, load‐carrying capacity, stress distribution, and failure mechanism. According to the experimental results, when the model is subjected to longitudinal bending moment, the failure mode is similar to that of pure bending of a girder, and when the model is subjected to transverse bending moment failure mode behaves like the flexural failure mode of the traditional reinforced concrete structure. A non‐linear element analysis is also made on the model with the results in good agreement with that of the experiment. The same modeling method is applied to the finite element analysis of the real bridge, considering various load in design. In the analysis, it is finally verified that this new type of bridge meets specification requirements in strength, rigidity, and resistance to cracking. [ABSTRACT FROM AUTHOR]

Abstract: Limitations on the use of partial shear connection in composite beams with single flange steel beams and composite dowels – Part 2: Analysis of the load bearing and deformation behaviour and modes for the minimum degree of partial shear connection. For composite beams with single flange steel beams and composite dowel connectors, the limitations to the use of partial shear connection have not yet been clarified. In this paper (continuation of [1]) the bearing and deformation behavior is analyzed using experimentally verified FE models. For this purpose, a comprehensive parametric study is performed, in which, in addition to the degree of shear connection and different cross‐sectional types, different parameters of the composite beam are varied which do not enter into the analytical calculation of the plastic bending moment capacity. These are, on the one hand, properties which depend on the static system, such as the loading situation (single load or uniformly distributed load) and the span, on the other hand, the slip deformation behavior of the connectors is varied by establishing different ductility characteristics for pry‐out and steel failure of composite dowels. Based on the simulation results, equations are derived for the minimum degree of partial shear connection for beams with single flange steel sections and composite dowel connectors including all required limitations of use for plastic design. The own models are compared to regulations given in a technical approval for composite dowels. The models may also be adopted for composite beams with steel T‐sections and horizontally lying shear studs. [ABSTRACT FROM AUTHOR]

Abstract: Failure of a steel pallet rack in Athens. Pallet racking systems have peculiar characteristics which differ from usual steel structures that make them sensitive to stability failure modes. In the present paper a rack failure is presented where the rack has failed due to lateral torsional and distortional buckling of its most stressed uprights. The structural behavior was studied by a combination of experimental and numerical/analytical methods. The investigations included test loading, bending tests on pallet beams, compression tests on stub column and bending tests on beam end connectors. Subsequently, a global geometrical non‐linear analysis is performed on the 3‐D system. Its results indicate by comparison with the pictures of the actual structure that the collapse mode is correctly detected. Conclusions are drawn that recommend the performance of static and dynamic analyses on an obligatory basis. [ABSTRACT FROM AUTHOR]