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.
Eurocode 8 is undergoing a thorough revision process encompassing a significant number of changes. In this work, the novel ductility classes, drift limits for damage limitation, local ductility ...conditions, and corresponding detailing prescriptions are presented and discussed. It is paramount to analyse and contrast these modifications with the current provisions of Eurocode 8. In order to assess the impact of such revisions, an extensive examination was conducted on ten symmetrical moment-resisting frame (MRF) buildings. These buildings are regular in plan and in elevation and are not torsionally flexible. The analysis was carried out following both the current and the second-generation Eurocode 8 provisions, with the results being compared in order to evaluate the effectiveness of the new design and detailing provisions. The study outcomes revealed that the DCM, DC2, and DC3 structures demonstrated different trends in their detailing demands for local ductility and capacity design. Differences in reinforcement quantities were observed between DCM and DC2, as well as DC2 and DC3, for 5-storey and 10-storey buildings. The design approach focused on individual member detailing requirements, to optimize design, while maintaining the overall concrete quantities. These insights offer valuable economic considerations for various structural configurations under strong seismic actions.
•The comparison between DCM - DC2 and DC2 - DC3, shows variations in the longitudinal and transverse reinforcement.•Buildings designed for DCM and DC3 ductility classes behave similarly.•There is a consistent linear trend where capacity design in shear exceeds seismic design demand for all ductility classes.•Capacity design in shear is generally higher than seismic design demand, indicating adequate shear resistance.•Some columns show substantially higher values, possibly due to higher moment values at lower storeys.
The 2013 European Seismic Hazard Model (ESHM13) results from a community-based probabilistic seismic hazard assessment supported by the EU-FP7 project “Seismic Hazard Harmonization in Europe” (SHARE, ...2009–2013). The ESHM13 is a consistent seismic hazard model for Europe and Turkey which overcomes the limitation of national borders and includes a through quantification of the uncertainties. It is the first completed regional effort contributing to the “Global Earthquake Model” initiative. It might serve as a reference model for various applications, from earthquake preparedness to earthquake risk mitigation strategies, including the update of the European seismic regulations for building design (Eurocode 8), and thus it is useful for future safety assessment and improvement of private and public buildings. Although its results constitute a reference for Europe, they do not replace the existing national design regulations that are in place for seismic design and construction of buildings. The ESHM13 represents a significant improvement compared to previous efforts as it is based on (1) the compilation of updated and harmonised versions of the databases required for probabilistic seismic hazard assessment, (2) the adoption of standard procedures and robust methods, especially for expert elicitation and consensus building among hundreds of European experts, (3) the multi-disciplinary input from all branches of earthquake science and engineering, (4) the direct involvement of the CEN/TC250/SC8 committee in defining output specifications relevant for Eurocode 8 and (5) the accounting for epistemic uncertainties of model components and hazard results. Furthermore, enormous effort was devoted to transparently document and ensure open availability of all data, results and methods through the European Facility for Earthquake Hazard and Risk (
www.efehr.org
).
This paper deals with the modelling and assessment of the inelastic cyclic behaviour of composite members consisting of steel beams and reinforced concrete slabs, designed to European standards. The ...work involves the development of detailed continuum models that can simulate the asymmetric behaviour and cyclic degradation characteristics of composite members. The generated model is first validated against available experimental results then used to investigate the influence of important parameters affecting the moment‐rotation relationships at the dissipative composite beam ends under cyclic loading. Based on the results, nonlinear relationships for modelling the response of composite members are proposed. It is shown that the degradation modelling parameters are most influenced by the cross‐section slenderness of the structural steel and the depth of the composite beam. Together with significant asymmetry in cyclic behaviour, around 20% higher cyclic degradation is observed in composite members compared to their bare steel counterparts. In addition to providing information required for the seismic design and assessment, the proposed expressions are utilised for the calibration of lumped plasticity models with cyclic degradation suitable for computationally efficient frame‐level analysis.
Eccentrically braced frames (EBFs) constitute a good structural solution located between Moment Resisting Frames (MRFs) and Concentrically Braced Frames (CBFs) because they exhibit an adequate ...lateral stiffness joined with a high ductility capacity, especially for what concerns short and very short links. Link design plays an important role in the effective dissipation capacity of the structure that is well designed only if the link members are involved in plastic range while the other members remain elastic. A proper design of the non-dissipative members needs to account for the link overstrength that results to be very high, especially for very short links.
In this paper, the influence of the axial restraints on the evaluation of the link overstrength and ultimate rotation is investigated. A wide parametric analysis is carried out based on a set of shapes selected in the European Standards. FEM simulations are used to develop the parametric analysis after a calibration carried out on experimental tests selected from a literature review. Empirical formulations are also proposed with the scope of providing a more accurate evaluation of the overstrength factor for short and very short links in the framework of EU “I shaped” standard profiles.
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•Numerical analyses of detailed finite element models (FEM) are carried out.•The effect of axial restraint on the plastic overstrength and ultimate rotation of EBF EU “I shaped” links is investigated.•A parametric analysis is reported to set up more accurate relations to evaluate the overstrength factor.•Overstrength factor formulations are proposed for both short and very short link, with and without the axial restraint.•The proposed formulations have partial safety coefficients to account for the model uncertainty.
•A design methodology aiming to assure a collapse mechanism of global type for MRF–EBF dual systems is reported.•This methodology called Theory of Plastic Mechanism Control (TPMC) is extended to the ...case of Moment Resisting Frames–Eccentrically Braced Frames (MRF–EBF) dual systems.•A number of MRF–EBF dual systems have been designed by TPMC and EC8 and their performances have been evaluated by means of push-over analyses.
In this paper, the closed form solution of the Theory of Plastic Mechanism Control (TPMC) is extended to the case of Moment Resisting Frames–Eccentrically Braced Frames (MRF–EBF) dual systems. As it is known, Eurocode 8 does not provide any specific design criterion regarding such structural typology, so that practitioners commonly carry out the design process by combining the design rules suggested for simple MRFs and EBFs. Therefore, the aim of this work is to provide a complete and exhaustive design procedure for MRF–EBF dual systems, considering all the brace configurations commonly adopted and with the goal of assuring the development of a collapse mechanism of global type. The design procedure to assure this ambitious design goal is based on TPMC whose aim is to derive the column sections required to assure the desired collapse mechanism starting from the knowledge of the dissipative zones. In order to point out the accuracy of the proposed design approach and the differences between itself and Eurocode 8, a number of MRF–EBF dual systems have been designed and their performances have been evaluated by means of push-over analyses.
Steel moment resisting frames (MRFs) are drift‐sensitive structures and their design is largely influenced by code requirements to limit the lateral displacements and to control the second order ...effects. Current and next generation of Eurocode 8 recommend different rules to verify the lateral rigidity and resistance of steel MRFs that lead to structures that are substantially different in terms of size of members and overall performance. In order to investigate the influence of the design rules on the seismic behaviour of ductile steel MRFs a parametric numerical study was carried out on 48 structures designed according to Eurocodes as well as US codes, the latter analysed as benchmark, varying the number of storeys, moment resisting spans and seismic intensity. The results of non‐linear static and dynamic analyses show that the structures complaint with current Eurocode 8 are the most expensive and characterised by the greater lateral rigidity and resistance, while MRFs designed in accordance with ASCE7 rules have the smaller profiles and the lower overstrength. The frames designed with rules of the latest version of next generation of Eurocode 8 have an intermediate behaviour even if closer to ASCE7‐compliant structures. These results are also confirmed by the probability of collapse that is smaller than the minimum value specified by EN1990 for the considered consequence class of the examined buildings.
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