In this study, a theoretical investigation is conducted on the local buckling resistance of aluminium Z-sections subjected to uniform compression. A method is developed based on the J2 deformation ...theory of plasticity (DTP) to calculate the critical buckling load within the elastic–plastic range. The deformation theory of plasticity relies on the assumption that the strain state is uniquely defined by the stress state. Consequently, it serves as a specific path-independent non-linear constitutive model. The study commences with the elastoplastic differential equation for a single compressed plate. By incorporating the boundary conditions and the interaction between plate elements, the interactive buckling load is determined. An example is provided to illustrate the incremental nature of the numerical procedure. Additionally, numerical analyses are performed to examine the impact of the strain-hardening properties of aluminium alloys on local buckling resistance. In the final stage, the theoretical results are compared with those found in existing scientific literature. This comparison serves to evaluate the accuracy of the DTP procedure.
The aim of this work was to study the ultimate behaviour of box-shaped aluminium members subjected to uniform compression. Eight stub column tests have been carried out at the University of Salerno. ...In particular, four box sections made of 6060 aluminium alloys with different width-to-thickness ratios have been investigated. The results have been reported in terms of the maximum compressive resistance and corresponding deformation capacity. Subsequently, the experimental results have been compared with those obtained by two accurate methodologies: (1) a theoretical procedure based on the deformation theory of plasticity (J2); and (2) an extension of the effective thickness method (ETM) provided by Annex L of the Eurocode 9 draft. These approaches take into account the local buckling effects within the elastic-plastic region, the strain-hardening be-haviour of the aluminium material, and the interaction between the plate elements constituting the cross-section. Finally, a comparison between new methodologies and current design rules has been presented.
This paper is aimed to discuss the conceptual troubles currently appearing in the codified rules to account for second-order effects in the seismic design of structures. First of all, starting from ...SDOF systems, the distinction between second-order effects in the elastic range and second-order effects in the plastic range is clarified. Moreover, the attention is focused on the conceptual difference occurring between a parameter measuring the structural proneness to second-order effects and a demand parameter measuring the safety level against the phenomenon of dynamic instability. Successively, the critical issues concerning the behaviour occurring in real MDOF structures when compared to SDOF systems is pointed out underlining the uncoupling between second-order effects in the elastic range and second-order effects in the plastic range, due to the influence of the collapse mechanism typology. The codified rules to account for second-order effects in Eurocode 8 are analysed showing why they are conceptually wrong giving rise to a lot of unjustified problems in the seismic design of steel MRFs. Recent proposals to improve Eurocode 8 are also analysed. Finally, it is shown how relevant studies already existing in the technical literature can be exploited in order to set up code provisions having a sound theoretical background. Finally, a new proposal, accounting for the influence of the collapse mechanism, for codification of P − Δ effects in seismic design is presented.
●In the case of SDOF systems, the stability coefficient is the only one parameter needed to measure the structural proneness to second-order effects both in the elastic range and in the plastic range.●The stability coefficient adopted by Eurocode 8 is not a parameter measuring the structural proneness to second-order effects.●Dynamic instability is a phenomenon related to the seismic displacement demand.●In the case of real MDOF structures, the structural proneness to second-order effects in the plastic range of behaviour is dependent on the collapse mechanism.●A new proposal for codification of effects in seismic design is proposed.●The proposal novelty is that it accounts for the need of amplifying the seismic design forces, directly accounting for the influence of the collapse mechanism typology.
The capacity of a structure can be assessed using inelastic analysis, requiring sophisticated numerical procedures such as pushover and incremental dynamic analyses. A simplified method for the ...evaluation of the seismic performance of steel moment resisting frames (MRFs) to be used in everyday practice has been recently proposed. This method evaluates the capacity of buildings employing an analytical trilinear model without resorting to any non−linear analysis. Despite the methodologies suggested by codes, the assessing procedure herein described is of easy application, also by hand calculation. Furthermore, it constitutes a suitable tool to check the capacity of the buildings designed with the new seismic code prescriptions. The proposed methodology has been set up through a large parametric analysis, carried out on 420frames designed according to three different approaches: the theory of plastic mechanism control (TPMC), ensuring the design of structures showing global collapse mechanism (GMRFs), the one based on the Eurocode 8 design requirements (SMRFs), and a simple design against horizontal loads (OMRFs) without specific seismic requirements. In this paper, some examples of the application of this simplified methodology are proposed with references to structures supposed to exhibit global, partial and soft storey mechanism.
The ultimate behavior of steel beams deeply influences the overall performance of steel frames. The main response parameters are the rotation capacity and the flexural ultimate resistance. The former ...is the source of the local ductility supply needed to achieve a global dissipative behavior of structures under seismic actions, whereas the latter governs the flexural overstrength whose knowledge is needed for an appropriate application of hierarchy criteria in seismic design of structures. Therefore, a twofold classification of steel members according to their ductility and overstrength is the most appropriate approach for seismic design applications. Currently, modern international design codes are based on the classification of steel sections for both plastic and seismic designs of structures, providing misleading emphasis mainly on local buckling as the primary strain-weakening effect. Even though different methods are available in the technical literature for predicting the ultimate behavior of steel members under non-uniform bending, the problem still deserves further investigations, because of the high number of parameters affecting the ultimate response and the variety of cross-sectional shapes. Therefore, a new experimental program dealing with a wide range of cross section typologies (I and H sections, Square and Rectangular Hollow sections) under monotonic and cyclic loading has been carried out by testing specimens with different local slenderness ratios properly selected to integrate the data already available in the technical literature. The obtained results are herein presented and discussed.
► A review of steel beam classification criteria is presented. ► Monotonic and cyclic tests on steel beams are presented and discussed. ► New empirical formulation for rotation capacity and overstrength is presented.
The ultimate behaviour of aluminium members subjected to uniform compression or bending is strongly influenced by local buckling effects which occur in the portions of the section during compression. ...In the current codes, the effective thickness method (ETM) is applied to evaluate the ultimate resistance of slender cross-sections affected by elastic local buckling. In this paper, a recent extension of ETM is presented to consider the local buckling effects in the elastic-plastic range and the interaction between the plate elements constituting the cross-section. The theoretical results obtained with this approach, applied to box-shaped aluminium members during compression or in bending, are compared with the experimental tests provided in the scientific literature. It is observed that the ETM is a valid and accurate tool for predicting the maximum resistance of box-shaped aluminium members during compression or in bending.
The main aim of this work is to validate the application of a simplified performance-based method for assessing the seismic performance of steel buildings, focusing particularly on Moment Resisting ...Frames (MRFs) through nonlinear analyses. This simplified method defines the capacity curve of a structure through elastic and rigid-plastic analyses, calibrated by regression analyses conducted on 420 structures. To assess its accuracy, the method was compared with other analytical approaches, including incremental dynamic analyses (IDA) provided by existing codes. These analyses were performed on both real structures and simulated designs, considering recent and older codes. The comparison of capacity results derived from code-based approaches and IDA, aligned with the limit states outlined in current codes, showcased the high reliability of the proposed simplified assessment approach.
The seismic events that occurred in the last decades have highlighted the importance of a correct design of the structures in seismic areas and the seismic inadequacy of a large part of the built ...heritage. Modern codes are still lacking in terms of prescriptions for the evaluation of the seismic performance of existing buildings. The present work proposes a simplified method for the evaluation of the demand in terms of plastic rotation for short links of steel Eccentrically Braced Frames (EBFs). A relationship for the evaluation of the demand, that exploits elastic analysis and rigid-plastic analysis extended to the second-order effects, is proposed. The calibration of this relationship was carried out on 420 EBFs equipped with short links designed according to three different approaches. The 420 frames have been also used to analyze the behavior in the plastic range of EBF type structures equipped with short links. The study also provides an extensive analysis on the influence of plastic redistribution capacity on the demand in terms of plastic rotations of links, corresponding to the achievement of the maximum bearing capacity. The obtained relation can be exploited as an assessment tool by comparing the demand with the link capacity. Moreover, from a performance-based design point of view, the same can be used for predicting the required ultimate plastic rotation as a function of the plastic redistribution capacity of the structure.
The capacity of a structure can be assessed using inelastic analyses, requiring sophisticated numerical procedures such as pushover and incremental dynamic analyses. A simplified method for the ...evaluation of the seismic performance of steel Concentrically Braced Frames (CBFs) to be used in everyday practice and the immediate aftermath of an earthquake has been recently proposed. This method evaluates the capacity of an existing building employing an analytical trilinear model without resorting to any non-linear analysis. The proposed methodology has been set up through a large parametric analysis, carried out on 420 frames designed according to three different approaches: the first one is the Theory of Plastic Mechanism Control (TPMC), ensuring the design of structures showing global collapse mechanisms (GCBFs), the second one is based on the Eurocode 8 design requirements (SCBFs), and the third is a non-seismic design, based on a non-seismic design (OCBFs). In this paper, some examples of the application of this simplified methodology are proposed with references to structures that are supposed to exhibit global, partial, and soft storey mechanisms.
Parametric Finite Element (FE) simulations were performed to investigate the ultimate flexural of different configurations of friction steel beam-to-column joints equipped with FREEDAM (free from ...damage) dampers. The main aim of this study was to compare the effectiveness of friction dampers featuring either single or multiple slotted holes, examining how these variations influence the behavior of the joint and the devices under seismic loads. In particular, the ultimate behavior of the connection (i.e., when the device reaches its maximum stroke) was investigated to characterize the involvement of the bolts in shear, the bearing of the plates, and the yielding of the supporting components. The analysis of bolt stress states revealed significant differences influenced by the number of bolts and slots. The FE models were calibrated against the experimental results obtained within the FREEDAM RFCS Project. These insights contribute to the design and performance evaluation of steel beam-to-column joints with FREEDAM connections, in particular the detailing of the haunch slots, laying the groundwork for future research and applications.
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