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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]

Free‐form reinforced concrete, prestressed concrete and composite components: Calculation of cross‐section values A resource‐efficient use of concrete as a construction material can be achieved by adapting the individual shape of a component under consideration to the stresses that occur and by arranging composite construction materials (e. g. reinforcing steel, prestressing steel or structural steel) in suitable areas of the component. Due to the advancing digitalisation in the construction industry, for example in the context of Building Information Modeling, computer‐aided 3D modelling methods are increasingly being used in the planning of structures. These allow engineers to design components in free form. In reinforced concrete, prestressed concrete and composite construction, the design of such components is currently still associated with great effort. In the context of the development of a practical method for the calculation of free‐form concrete components, this paper presents a CAD‐integrated method for the calculation of cross‐section values. Cross‐section values are required as an essential calculation basis when real, three‐dimensional structural components are treated using simplified calculation theories, such as the beam theory. In this paper, the mathematical and numerical fundamentals of a method for the calculation of cross‐section values of free‐form concrete, reinforced concrete, prestressed concrete and compound components are presented. The calculation method is based on flat geometric regions described by Non‐uniform rational B‐Spline tensor product surfaces, which can be extracted from solid models, for example. [ABSTRACT FROM AUTHOR]

Modelling of the CUBE's TWIST shell This paper gives an overview of the main procedures prepared during the phase of the project development within the field of numerical modelling and design. The roof shell elements represent itself twisted shape that together with complicated structurally demanded inner structure forms quite complicated configuration for the concrete volumes as well as for the used reinforcement. Therefore, custom developed numerical method was required to be prepared. For that, the software solutions Rhinoceros 3D and Grasshopper 3D were used as the main algorithmic environment. The paper additionally gives an insight of important aspects required for production of the formwork components, thermal insulation, biaxially oriented carbon reinforcing grids and other parts of the load‐bearing shells. Finally, the paper gives an idea how was established a collaboration with partners of the CUBE project in particular in the field of structural analysis. [ABSTRACT FROM AUTHOR]

Increase of technical lifetime of infrastructures based on semi‐probabilistic considerations One of the most important measures in the discussion on improved sustainability in construction is to extend the service life of our structures [1]. Therefore, intensive research is conducted with regard to changing environmental conditions as well as external load effects for structures and new materials and their impact on the production and operation of infrastructures. Already now, according to [2], changes in the kinematics of the degradation mechanisms can be observed. In particular, changing environmental conditions (exposures) can accelerate but also slow down the degradation of materials and structures. These understandings of the degradation processes, but also the improved knowledge of the geometry and effective mechanical building material properties, should be effectively transferred into engineering practice for the assessment of structural reliability and remaining service life [3]. This paper presents how the elements of reliability analysis can be combined with the elements of in‐depth testing and monitoring procedures to periodically evaluate the degradation processes due to changing environmental conditions and new building materials. Subsequently, the remaining service life can be continuously updated with the help of semi‐probabilistic partial safety considerations. [ABSTRACT FROM AUTHOR]

Experimental investigation on the effect of static system and load arrangement on the shear resistance of beams with low amounts of shear reinforcement In this paper, an experimental investigation on the shear behaviour of beams with low amounts of shear reinforcement and different static systems is presented. Four simply supported beams under concentrated loads, ten cantilevers and three simulated continuous beams under uniformly distributed loads were tested. The shear reinforcement ratio was varied between 0 (without shear reinforcement) and 2.0 times the minimum shear reinforcement according to EC2. The test results show a significant influence of the static system and the loading type on the crack pattern and ultimate load of the beams tested. While a reinforcement level below the minimum shear reinforcement has almost no influence on the shear resistance of simply supported beams under concentrated loads, a very low shear reinforcement leads to a significant increase in the shear capacity of beams under uniform distributed loads. The crack pattern, however, remains unchanged compared to beams without shear reinforcement where shear failure is characterized by a single critical shear crack. The test results were also compared with design and standard specifications. The comparisons show possible improvement potentials in the currently applied models. [ABSTRACT FROM AUTHOR]

Double‐headed studs as shear and punching reinforcement – Current status and outlook Double‐headed studs have been established for decades as a very effective punching shear reinforcement because these reinforcement elements, which are optimized for shear and punching loads, combine a particularly high anchorage performance with a practicable installation on site. In this paper, an overview of current usability and applicability verifications for double‐headed studs in Germany is given. Afterwards, the currently valid design and construction rules for the use of double‐headed studs as shear reinforcement as well as punching reinforcement are summarized. Finally, the next Eurocode 2 generation 2023+is looked at, with excerpts presenting some significant innovations in the future integration of double‐headed studs into the shear and punching rules. [ABSTRACT FROM AUTHOR]

Influence of the arrangement of the punching shear and composite reinforcement made of L steel plates on the load‐bearing capacity The CLIXS punching shear and composite reinforcement system consists of L steel plates with one or two connected stirrups made of reinforcing steel. It is possible to increase the load‐bearing capacity by more than twice the load‐bearing capacity without punching shear reinforcement. The experimental investigations described in the paper were carried out on square slab cut‐outs with a length of 2.8 m and a thickness of 18 and 25 cm. The load‐bearing capacity as a function of the number of uniform arranged L steel plates was determined based on 17 experiments. For this purpose, test specimen with 6 L steel plates up to 36 L steel plates in the first three perimeters were investigated. In addition, 10 test specimen with different sized areas without L steel plates were tested. The areas without L steel plates were between 25 % and 75 % of the area within the first three perimeters. The use of stirrups with a diameter of 8 mm instead of 6 mm was investigated using two test specimens. [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]

Shape optimisation of eccentrically loaded columns – theory and experimental verification. In shape optimisation, the external shape of the structural component is adapted to the predominant force flow. In this way, large load increases can be achieved with the same material use, or high material savings can be achieved with the same load‐bearing capacity. In this paper, a shape optimisation for eccentrically loaded columns is presented, where the bending stress results from a frame effect of the load‐bearing system. This is the case, for example, in edge columns of typical reinforced concrete skeleton structures, as they are usually used in residential and commercial buildings. The shape optimisation method presented in the article can be applied to columns with an arbitrary ratio of a moment‐normal force loading, provided that a material failure occurs. Results for shape optimisation in the case of a stability failure have already been published separately for centrically pressed columns. The optimisation itself is carried out iteratively on a column segmented over the height under the criterion of achieving a uniform stress state in the component. With the help of an experimental check on 3.3 m high columns, the selected calculation and optimisation method could be verified. In addition to the failure loads, the concrete strains and the deformation behaviour were also analysed and evaluated at selected points of the specimen. [ABSTRACT FROM AUTHOR]

Punching shear in irregular flat slab systems – Recommendations for modeling and design The punching shear verification is often the decisive verification in design due to the concentrated load introduction. Moreover, uneven shear stress distributions often occur in the punching shear area as result of irregular flat slab systems or eccentric loads. In structural design it is often questionable, how a non‐uniform shear stress distribution can be considered with acceptable effort. The direct determination of the shear stress distribution along the control perimeters using FE methods is not explicitly excluded in the current Eurocode 2 but is also not described in more detail. This gives considerable freedom in design for the structural engineer, but also ambiguities for interpreting the results. In this paper, FE approaches for determining the factor β or for directly considering the non‐uniform shear stress distribution are presented and analyzed based on an application example. Finally, recommendations and modelling advice are given for the pragmatic and, as far as possible, realistic determination of factor β for consideration of unbalanced moments. [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: Practical Application of an innovative concrete shell construction method: Construction of the deer pass AM2 by use of PFHC Concrete shells are aesthetic and economic supporting structures, if properly designed. They can absorb high loads and can span large areas with little material. Unfortunately, high costs for the complicated formwork avoid a wider use in practice. A new shell construction method called Pneumatic Forming of Hardened concrete (PFHC) was developed at the Institute for Structural Engineering at TU Wien. Within a tight development process numerous material tests, tensile tests, bending tests and two large scale experiments were performed. Now, the Austrian railways (ÖBB) used the construction method to build the deer pass AM2 as concrete shell bridge over the two‐rail track Koralmbahn in Carinthia in Austria. At first a test shell, which now serves as event canopy, was built with the plan dimensions 26.5 × 19.1 m and a height of 4.2 m. Directly after that the main supporting structure, the shell bridge, was built (plan dimensions 36.2 × 38.7 m, height 8.1 m). The first part of the paper which was published in the previous issue summarizes the development process of the new building method. Furthermore, the paper describes the building process of the two shell structures and chosen experiments for the construction process. Finally, the monitoring concept is explained. [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]

About the design concept for compressive fatigue loading of concrete - Structure of the fatigue design concept For building structures exposed to fatigue loading, especially for those made from high-strength concrete, the fatigue design is decisive for the structural design. Coincident, nowadays new experimental results exist which demonstrate that further developments of the fatigue design concept are expedient and necessary. The safety concept for fatigue design was assigned from the static design concept. From this approach, particularities and challenges arise for the further development of the design concept. In this paper the structure of fatigue design is described. Furthermore, the enclosed parameters are explained and their relevance in the context of safety considerations is discussed. Based on this, outstanding issues are identified for the further development of the design concept. In part 2 of this paper the safety concept of the fatigue verification is discussed and the potential of further developments is pointed out. [ABSTRACT FROM AUTHOR]

Abstract: In‐situ tests at the bridge Hammelburg regarding the shear capacity of existing pre‐stressed bridges Part 2: Measuring concept, results of the in‐situ tests, comparison with different theoretical approaches Due to the relatively high average age of the existing bridges, a dramatic increase in traffic volume and axle loads and modified design standards, a realistic prediction of the shear capacity of existing pre‐stressed concrete bridges with little shear reinforcement has become an important topic in research. In 2017 the Chair of Concrete and Masonry Structures of the Technical University of Munich (TUM), supported by the Federal Ministry of Transport and Digital Infrastructure, was able to conduct unique field tests at the 1955 built Saalebrücke Hammelburg. According to systematic strength evaluations many concrete bridges, especially those which have been built prior to 1966, show severe (theoretical) deficits regarding the longitudinal shear capacity. Often the results of the strength evaluation cannot be verified at the real bridges though. The primary objective of the field test was therefore to determine the shear capacity of existing pre‐stressed bridges in order to contribute in closing the gap between calculations and experience for older concrete bridges. In the first part of this article the general assessment of the bridge and the original design concept as well as the conceptual approach, the execution of the in‐situ tests and the used measuring equipment were described. In the present paper the measuring concept and the results of the conducted tests are presented. Furthermore, the results of the in‐situ tests are discussed, and the measured maximum loads are compared to the results of different theoretical approaches and engineering models, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In‐situ tests at the bridge Hammelburg regarding the shear capacity of existing pre‐stressed bridges – Part 1: General assessment, original shear design, conceptual approach and execution of the in‐situ tests Due to the relatively high average age of the existing bridges, a dramatic increase in traffic volume and axle loads and modified design standards, a realistic prediction of the shear capacity of existing pre‐stressed concrete bridges with little shear reinforcement has become an important topic in research. In 2017 the Chair of Concrete and Masonry Structures of Technische Universität München (TUM), supported by the Federal Ministry of Transport and Digital Infrastructure, was able to conduct unique field tests at the 1955 built Saalebrücke Hammelburg. According to systematic re‐analyses many concrete bridges, especially those which have been built prior to 1966, show severe (theoretical) deficits regarding the longitudinal shear capacity. Often the results of the strength evaluation cannot be verified at the real bridges though. The primary objective of the field test was therefore to determine the shear capacity of existing pre‐stressed bridges in order to contribute in closing the gap between calculations and experience for older concrete bridges. In the present paper the general assessment of the bridge and the original design concept as well as the conceptual approach and execution of the in‐situ tests are presented. In the following part 2 of this article the results of the conducted full‐scale tests will be discussed. [ABSTRACT FROM AUTHOR]

Abstract: Glass beams in analogy with Eurocode 2 – An analogy between pre‐compressed glass and concrete beams: Glass and concrete share some essential material characteristics: Their compressive strength exceeds their tensile strength considerably and both of them fail in a brittle manner. Therefore, it is reasonable to build beams from both materials based on the same principles and to transfer the knowledge from concrete design to the structural use of glass by an analogy study. First, a reference in a historical context between Franz Dischinger und the contemporary structural use of glass is made. A comparison of relevant material properties and structural details as well as a presentation of executed building projects follows afterwards. This demonstrates the applicability of structural details in glass design and shows the relevance to create a nomenclature for glass structures in analogy with the principles of reinforced and prestressed concrete design. Additionally, the paper introduces “Spannglass Beams” that entail a post‐tensioned steel cable to counteract initial cracks, uplift the member and ensure a sufficient post‐fracture bending capacity. Advanced problems such as the loss in tension force or a proof of feasibility of those structures is addressed. In conclusion, this makes the expertise from concrete design available to create novel and efficient load‐bearing glass structures. [ABSTRACT FROM AUTHOR]

Abstract: Fire design of reinforced and prestressed concrete columns – To practical use of Method A in DIN EN 1992‐1‐2 This paper provides practical guidance on the fire design of reinforced concrete columns using Eurocode 2 (DIN EN 1992‐1‐2) Method A by giving explanations, diagrams and extended tables for columns with fire exposure on more than one side and on only one side. For columns fire exposed on one side extended tabulated data are given, which were calculated with the Advanced calculation method. [ABSTRACT FROM AUTHOR]

Abstract: Contribution concerning load bearing behaviour of CFRP confined RC columns with circular cross section Beside CFRP (Carbon Fiber Reinforced Polymer) strips, which are successfully utilized as an additional glued reinforcement in tension zones of existing reinforced concrete (RC) members, CFRP sheets gain more and more attention in terms of strengthening and retrofitting. Those sheets are capable to increase the bearing capacity of RC slaps and beams significantly. Furthermore, CFRP sheets can improve the capacity of RC columns, too. In doing so, the connection of concrete surface and CFRP sheet is enabled by an epoxy resin (CFRP confinement). Thereby, concrete's lateral expansion is efficiently restricted in cases of imposed axial compressive deformation; therefore, the elastic CFRP resisting response generates an ever increasing lateral compressive stress state on concrete, leading to structural upgrade of the member core to provide a remarkable higher concrete strength and sufficient deformability. Regarding CFRP confinement design in Germany, this paper presents a brief overview concerning the state‐of‐the‐art, and it introduces a design procedure utilized in German DAfStb‐Guideline „Strengthening of concrete structures with adhesive bonded reinforcement“. Furthermore, some recent research efforts and findings to improve the current model will be offered, too. [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: Calculation of the deflection of reinforced concrete members – general procedures for slabs and beams This paper introduces the fundamental procedures to calculate the deflection in the cracked state taking into account creep and shrinkage. A range of different methods with various degrees of accuracy is presented for beams and one‐way slabs, based on the guidelines of EC2. For simple systems these methods can also be used for hand calculations, permitting a high degree of control over the procedure. Subsequently, the usually rather complex calculation of deflections caused by the shrinkage of the concrete is considered in more detail. For a selection of systems, diagrams containing coefficients for a more efficient estimation of shrinkage deflections can be derived. Furthermore, the cracked state deflection of concrete slabs is addressed more closely. It can be calculated with the help of suitable finite element programs or using simplified manual procedures. The basic principles can be transferred from the previously considered beam structures. However, other influence factors have to be addressed, such as the procedure to reduce the flexural stiffness and the redistribution of the internal forces caused by cracking. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue strength of RC beams without transverse reinforcement under cyclic loads The shear design of RC members without transverse reinforcement (e.g. slabs, bridge decks, footings of wind energy plants) for fatigue loads is based on empirical approaches, which had been rarely validated by experiments. This paper presents theoretical, experimental and numerical studies, which aim to give a better understanding of the load transfer in RC members without web reinforcement under static as well as cyclic loads. Furthermore, the approach of Eurocode 2 will be examined. [ABSTRACT FROM AUTHOR]

Abstract: Rib shear connectors with concrete break out failure subjected to tension or compressive loads – Part 1: Finite Element Analysis The shear connectors in steel‐concrete composite structures have to provide sufficient resistance against stresses acting orthogonally to the shear connection leading either to uplift of the concrete slab or mutual penetration of the steel girder and the concrete. While the anchoring behavior of headed studs has been extensively researched in the past, investigations in the load bearing behavior of composite dowels subjected to tension and compressive loads are missing, to date. Therefore, the present paper describes finite element investigations in the load bearing behavior of composite dowels exposed to loads acting orthogonally to the shear connection. The FE‐model, validated against tests from literature, is used to investigate the transfer of stresses between steel dowel and concrete and to clarify the influence of different parameters, like the effect of transversal reinforcement in the concrete and the size effect of the anchorage depth. In the second part, the FE‐results are used to derive engineering models and design approaches for composite dowels subjected to tension or compression. [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: Planning and structural design of water‐tight concrete constructions – basic design principles and their structural realization In water‐tight concrete constructions, the reinforced concrete structure in combination with planned joint sealings on the one hand and with subsequent crack injections on the other hand is also securing a defined sealing function against water exposure. The utilization demands on water‐tight constructions have been raised significantly over the past years leading in the same degree to higher demands on quality of planning and building processes for these constructions. Present water‐tight constructions are high‐performance structures whose demands on the planning process exceed the common knowledge in architectural and structural design by far. There is general planned about the quality‐regulating, constructive aspects (reduction of constraint stresses, concrete technology and post‐curing) for these structures. But regarding the analytical calculation models for constraint forces, a huge scatter in assumed exposures and resistance as well as a fuzziness of existing models have to be noticed leading to non‐reproductive and blurred calculative design results. This paper is focussing on exposures and resistances as well as on different calculation models leading to practical recommandations for the structural design which is only insinuated in the basic rules for water‐tight constructions. [ABSTRACT FROM AUTHOR]

Abstract: Material characteristics of a historical reinforced concrete bridge – A report about material investigations on existing structures, dedicated to Jürgen Schnell's 65th birthday The determination and characterization of material properties of existing structures is a current focus of research by Prof. Schnell, to whom the article is dedicated. The recent published books of the DAfStb (publication series nr. 616 and 619) provide the expedients for the practicing engineer to determine material strength to evaluate existing structures. Within a historical project on the former civil engineer and professor of the TH Dresden Willy Gehler, the properly oldest reinforced Hennebique concrete bridge of middle Germany was found. The bridge was demolished in 2016 because of a limited flow rate. At least this offers the opportunity to obtain sample material. The investigations on the material behavior were described in the paper as well as a discussion on the difficulty for its determination of values for recalculation. [ABSTRACT FROM AUTHOR]

Abstract: Load‐bearing capacity of unreinforced concrete compression members under biaxially eccentric loading Compression members, such as columns or walls, have to carry vertical loads primarily. Due to the rotation of the adjacent components, they are also subjected to bending moments. If the compression member is, in addition to the bending moment about the weak axis, also loaded by horizontal bracing forces in direction of the strong axis, bending moments about both axes (biaxial bending) occur. This paper deals with the load‐bearing capacity of slender, unreinforced and biaxially eccentrically loaded compression members made of concrete. Existing theoretical methods for determining the load‐bearing capacity of centrically and uniaxially eccentrically loaded compression members are shown as well as the corresponding normative regulations. On this basis, two practice‐oriented proposals for determining the load‐bearing capacity of biaxially eccentrically loaded unreinforced concrete compression members are presented. The proposals can easily be adopted into the standard and thus, the existing restricting limits of application can be neglected. [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]

Methods to reduce the partial safety factor concerning dead loads of existing bridges The recalculation guideline for existing concrete bridges allows to reduce the partial safety factor for dead loads from γG = 1.35 to 1.20 which matches a conservatively estimated model uncertainty factor. Pre-requisite is that geometry, concrete's specific weight and reinforcement ratio are known from sufficient und representative measurements on-site. In recalculation according to the guideline, the dead load variation driven by these three factors is considered directly by the load distribution. However, no details on required accuracies of the measurements are specified at all. This paper shows how tailor-made partial safety factors can be derived from on-site measurements and supplemented with empirical data from literature. For existing bridges, it seems appropriate to measure the geometry and to estimate the variation of concrete's specific weight while the reinforcement ratio is taken from construction drawings. For application a reference bridge is jointly measured in cooperation with the land surveying office of the state capital city Düsseldorf. 3D laser scans and multicopter over-flights deliver a digital model. In general, the presented approach is relevant for recalculation, modification and deconstruction matters of existing bridges. [ABSTRACT FROM AUTHOR]

In [1] a design methodology is presented for the seismic design of structures, using realistic cracked member stiffness and explicitly allowing for additional wall displacements related to torsion. Because the methodology is only suited for earthquake design separately in the principal directions of the building, the question arises whether a building so designed will also be safe for skew earthquake actions. In order to address this problem this paper presents the application of the proposed methodology, [1], to two example structures in each principal direction. These two buildings are then analysed using the program ETABS, first in one principal direction and then for lateral loads at a 45° angle. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the effect of structural system and load configuration on the shear behavior of flexural reinforced concrete (RC) members without shear reinforcement. A total of ten rectangular beams with three structural systems and two load configurations were tested. With the chosen test set-up, almost all M/V-combinations commonly encountered in practice can be investigated. The test results indicate significant differences of the shear capacity of members with different M/V-combinations. The shear capacity of the simply supported beam under a uniform load is higher than that of similar beams under a concentrated load. Moreover, the shear capacity of the cantilever and continuous beams under uniform load is significantly higher than that of simply supported beams. Generally, it can be concluded that the co-existing flexural action has a positive influence on the shear resistance of a RC member without shear reinforcement. Furthermore, the flexural crack pattern plays an important role in the shear resistance of slender RC members. [ABSTRACT FROM AUTHOR]