The calibration of appropriate buckling curves for interactive local/distortional-global buckling of thin-walled cold-formed steel members is a task well covered by the Erosion of Critical ...Bifurcation Load (ECBL) approach. In this context, here a modified formulation of the ECBL approach, based on a new definition of the mode interaction point, is presented. The Generalized Beam Theory is used to find the mode interaction points and the related imperfections. Pallet rack uprights in compression are studied to show the potentialities of the modified ECBL approach and mark the differences with the classical one. The buckling curves coming from the modified ECBL approach are also compared with experimental results and with the buckling curves evaluated following the EN15512:2009.
•A new formulation of the ECBL approach is proposed.•The GBT is used to find the interaction points and the related imperfections.•Pallet rack uprights in compression are studied as test cases.•Numerical results of the new ECBL approach are compared with those of the classical one, experimental results and EN15512:2009.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The growth of industrialization and the rapid expansion of densely populated urban areas have increased the risk caused by technological and man-made hazards. In particular, the accidental or ...intentional detonation of high explosives (e.g., improvised explosive devices IEDs), can cause damages to buildings and infrastructures and severe harm people. These risks can be minimized by a better planning, design, and construction, e.g., avoiding brittle construction materials, especially within the building envelope, and adopting more robust construction techniques. The study presented in the paper investigates the capacity of light steel-based wall panels to resist the effects of external explosions. The experimental results showed the ultimate capacity of the wall panels is strongly dependant on the initial design conditions and panel-to-structure fastening solution. A numerical model has been also calibrated using Etabs program.
•Four types of seismic moment connections tested under column loss scenario.•Two full strength connections and two partial strength connections.•Finite element models validated against experimental ...data.•Three connections experienced large deflections prior to failure.•Partial strength connection requires strengthening to improve deformation capacity.
The beam-to-column connections of moment-resisting steel frames should exhibit capacities that allow them to transfer the forces that develop under normally expected loading conditions. However, when a column is lost owing to accidental loading, these conditions change, and the forces are redistributed to the adjacent beams and columns. In such cases, the connections must be capable of resisting the combined axial and flexural loads and allow for the redistribution of the loads, so that progressive collapse development is prevented. In this study, we investigated the performances of four types of beam-to-column connections, namely, the welded cover plate flange connection (CWP), the haunch end plate bolted connection (EPH), the reduced beam section welded connection (RBS), and the unstiffened extended end plate bolted connection (EP), against progressive collapse. Two span frames were constructed and tested under a central column removal scenario until failure. The results from the experimental tests were used to validate finite element models. The CWP, EPH, and RBS specimens showed good ductility, with the catenary action making a significant contribution to the ultimate load resistance. Further, the ultimate rotations of the beams were greater than the deformation limit given in the latest Unified Facilities Criteria guidelines for design of buildings to resist progressive collapse. Specimen EP showed the lowest ductility and ultimate load resistance, with the bolts in the rows under tension fracturing before the catenary action could develop. Further, the failure mode for specimen EP indicated that bolt strengthening is necessary for improving its progressive collapse resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The difference between local and distortional buckling of thin-walled cold-formed steel sections with stiffened elements, of members in both compression and bending are taken into consideration ...applying relevant design formulas available in the codes. However, for unstiffened elements, or for those unstiffened enough, the difference between distortional and local buckling modes, in some cases, and particularly for U-, Z- and L-sections, might be unclear. When these sections are edge stiffened, in the case of lipped flanges, it is not always easy to identify which of the two are dominant, while in the case of interaction with an overall buckling mode, the situation might be even more difficult. Local buckling modes involve the buckling of cross-sectional walls, while distortional buckling, also known as “stiffener buckling” or “local-torsional buckling”, is characterised by the rotation of the flange at the flange/web junction in members with edge stiffened elements. Both types of buckling are also known as “sectional” buckling modes. For interactive local/distortional buckling with the overall one, the correct evaluation of the “short” member capacity might play a significant role when checking the design capacity of a slender thin-walled member prone to interactive sectional-overall buckling mode. In the case of a stiffened flange, the effectiveness of the stiffeners can make the difference between local and distortion buckling. A boundary between local and distortional bucking of a given open section can be established to be considered in the design. To correctly apply the Ayrton–Perry formula, in order to get the ultimate capacity of a thin-walled cold-formed steel slender member, prone to interactive local or distortional buckling with the overall one, the strength of the short member has to be identified. This paper summarises the study of this problem, including the main results and conclusions, emphasising that it is difficult to separate the local and distortional modes in the case of cold-formed steel open sections used in practice, and there is some interaction between these two modes.
•Local/distortional and overall interactive buckling of thin-walled cold-formed steel columns.•Effectiveness of edge stiffeners in the interactive buckling of open section.•Interactive buckling through the Erosion of Critical Bifurcation Load (ECBL) method.•Relevant results and graphic comparison related to the performance of the approach.•Design approach to consider the interactive local–distortion failures of members.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
During the European research project entitled EQUALJOINTS (European pre-Qualified steel JOINTS) 1, which recently concluded, the matter of providing a set of pre-qualification procedures for moment ...resisting beam-to-column connections which are currently used in Europe has been addressed. During the experimental campaign 24 specimens with bolted extended end-plate connections with haunches were tested. The current paper presents the numerical model which has been developed such that numerical testing may be performed to further investigate specific details. In what concerns the material, an isotropic material model has been calibrated and used based on tensile tests of coupons extracted from the specimens to model the actual plastic behaviour. Moreover, the imperfections of the beam have been taken into account using a bucking analysis to model as accurate as possible the specimens tested. The interaction between parts has been modelled using contacts with different interaction laws. The model used for the bolt has been calibrated such that the preloading and failure replicate the behaviour of the actual bolts used in the experiments.
Modelling the cyclic response of structural steel plays an important role in the design and performance assessment of steel structures. Up to date, several mathematical models were developed to ...simulate metal plasticity, but only some of them were implemented in Finite Element Method (FEM) based software packages such as Abaqus, by using incremental plasticity procedures. Within this article, the “built-in” combined isotropic/kinematic hardening model is used to model metal plasticity under cyclic loading regime. A brief description of the constitutive model together with the calibration procedure of the material parameters based on experimental data are presented. Finite element analyseswere carried out on simplified FEM models to provide numerical predictions using the calibrated material parameters. Since the “built-in” combined model has several limitations (especially related to the isotropic component), adjustments of the material parameters were made to accommodate to different loading histories. The chosen material model and the calibrated input parameters are validated byanalysing the FEM predictions to be in good agreement with the experimental results with respect to cyclic behaviour and failure mode.
In the case of an ideal structure, the theoretical equilibrium bifurcation point and the corresponding load, Ncr, are obtained at the intersection of the pre-critical (primary) force–displacement ...curve with the post-critical (secondary) curve. For a real structure, affected by a generic imperfection the bifurcation point does not appear anymore and, instead, the equilibrium limit point is the one characterizing the ultimate capacity, Nu, of the structure. The difference between Ncr and Nu represents the Erosion of the Critical Bifurcation Load (ECBL), due to the imperfections. This model applies in the instability mode interaction. The meaning of mode interaction inherently refers to the erosion of critical bifurcation load in case of interaction of two (or more) buckling modes associated with the same, or nearly the same, critical load. A well-known example of such a mode interaction is the one resulting from the coupling of local or distortional buckling with overall buckling in the case of thin-walled cold-formed members. Van der Neut 1 stated the erosion due to coupling and imperfection effects is maximum in the local–global coupling point. The ECBL approach extracts its basic principle from this conclusion. This is a review paper of which purpose is to summarize the mode interaction problem and ECBL approach, presenting the last results obtained by the authors.
•van der Neut column model for local–global buckling mode interaction offers the physical background of ECBL approach.•The Ayron–Perry equation enabled the relationship between the generalized imperfection and the erosion of theoretical buckling strength for interactive buckling.•ECBL can be regarded as a practical method to calibrate buckling curves for mode interaction problems, in the European format.•This procedure allows the calibration of α imperfection factor used to determine the design buckling resistance according to EN 1993-1-1.•ECBL can be applied for imperfection sensitivity studies or to set the imperfections corresponding to different imperfection scenarios.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Redistribution capacity and development of catenary action in case of column loss were assessed experimentally.•Robust moment connections allow development of catenary forces in beams and improve ...robustness.•Two-way frame system enhances redistribution capacity over planar systems as loading demand on each element reduces.•Applied element method was used to validate numerical model.
Multistory steel frames are expected to provide resistance to progressive collapse following local damage or failure caused by extreme loading events. Features like ductility and continuity provide more deformation capacity and redistribution of loads so that the structure can bridge over damaged elements. Special measures should be taken to ensure that the connections can withstand the extreme loading and deformation demands arising from the occurrence of local failure. In addition, two-way frames will enhance the progressive collapse resistance over planar systems as the loading demand on each element reduces.
In this study, we investigated the response of two-way steel frame systems under the removal of a central column. Extended end-plate bolted connections were used to join the beams to the columns. First, an experimental test was carried out, and then, a numerical model was validated using the advanced nonlinear dynamic analysis software Extreme Loading for Structures. The system was capable of developing large deformations associated with catenary response in the beams without failure of the connections. The beam ultimate rotation is larger than the deformation limit given in the codes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In recent years important research activity has been undertaken in order to evaluate the earthquake performance of light-gauge steel-framed house structures. Almost all studies approach the problem ...of seismic response of these structures by characterising, experimentally and numerically, the performance of wall panels. Usually, the overall behavior of wall panels is mainly addressed. However, according to experimental evidences, the performance of the wall panels, as a whole, is governed by the performance of the connectors e.g.: sheeting-to-sheeting connectors, and sheeting-to-framing connectors. On the other hand the global behavior of the 3D structure of the house is significantly influenced by non-structural elements, traditionally not considered in the design procedures. The present paper summarizes the research activity carried out in the last few years at the Politehnica University of Timisoara, under the coordination of the author, with the aim to evaluate the performance and to characterise for design purpose the specific features of these structures. Monotonic and cyclic tests on full-scale shear panels, tests on connection details, and in situ ambiental vibration tests on a house under construction are reviewed and concluded in the following paper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Dual frames with removable links provide a structure with re-centring capability.•The re-centring capability was validated through a full-scale experimental programme.•Good re-centring of frame with ...links not connected to the slab was observed.•The links can be removed by unbolting if permanent deformation after earthquake is small.•Flame cutting of links is recommended if larger permanent drifts occur.
Modern seismic codes allow for inelastic deformation in dissipative zones during design earthquakes, accepting damage to the relevant structural parts to a certain extent. Experience has shown that repair work is needed after moderate to strong earthquakes. The use of structural systems that are easily repairable is therefore beneficial in seismic regions. For a structure to be repairable, in addition to constraining any inelastic deformation to removable dissipative members, any permanent (residual) drift should be eliminated. To realise a re-centring capability in a structure with eccentrically braced frames (EBFs) and removable dissipative members, a dual structural configuration is used, which combines EBFs and moment-resisting frames (MRFs). If the more flexible MRFs are kept elastic, they would provide the restoring force necessary to re-centre the structure upon the removal of the damaged removable links (the dissipative members). This paper presents an experimental validation of the re-centring capability of a dual eccentrically braced frame with replaceable links, based on a full-scale experimental testing programme, performed at the European Laboratory for Structural Assessment (ELSA) at the Joint Research Centre (JRC) in Ispra within the framework of the Transnational Access of the SERIES Project. The experimental set-up, programme, and instrumentation are described. The results attained through the re-centring of the structure are presented, as well as its overall seismic performance and information on the interaction between the steel frame and the reinforced concrete slab in the link region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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