The design procedure codified within current Eurocode 8 for dissipative moment resisting and concentrically braced frames have led to the design of massive systems characterized in the most of cases by poor energy dissipation capacity. The research activity presented in the current paper addresses the identification of the main criticisms and fallacies in the current EN 1998-1 for those seismic-resistant typologies. In this regard, the design provisions and codified rules for both moment resisting frames (MRFs) and chevron concentrically braced frames (CCBFs) are critically discussed and numerically investigated. Static and incremental dynamic analyses were performed on a set of 3 and 6-story frames designed compliant to EN 1998-1. The results from the numerical analyses are reported and discussed.

No abstract

Background: Steel beam-to-column joints are generally designed and analysed considering the response parame-ters in their main bending plane, disregarding the influence of the connections and the related beams in the transverse direction. However, the 3D response of the joint can be influenced by the presence of the transverse beams in the case of column loss scenario. Objective: The objective of the study is to investigate the influence both the influence of the transverse beams and the potential effectiveness of the design rules developed within the research project EQUALJOINTS in case of column loss scenarios. Method: A comprehensive set of parametric finite element analyses was carried out. Three external joints were selected, and two types of column loss scenarios were investigated for 2D and 3D joint configurations. Results: The obtained results show that the presence of the secondary beams is beneficial to arrest the progressive collapse since it increases the resistance of the joint assembly, reducing the plastic demand into the primary moment-resisting joint. Conclusion: The presence of the secondary beams improves the joint performance under column loss thanks to their torsional stiffness; when the dimensions of the double cleat connection are comparable with those of the primary moment resisting joint, they are also able to increase the stiffness of the entire joint. Severe plastic deformation can be observed in the double cleat connections in joints directly affected by the column loss. Therefore, these connections should be properly designed in order to guarantee adequate ductility.

Bolted extended stiffened end-plate beam-to-column joints are commonly used for steel moment resisting frames in seismic areas. In the framework of European codes, EN 1993:1-8 provides the design rules and the analytical models to predict the mechanical behavior of the joints. On the other hand, EN 1998-1 specifies the required performance for seismic resistant joints. Within EQUALJOINTS project design rules have been developed and experimental tests were carried out to seismically prequalify extended stiffened end-plate joints. In this paper the proposed design rules are discussed and results of the experimental tests are described.

Chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility in the framework of Eurocode 8: differently from North American codes, lower values of behavior factors are recommended by EN 1998 for C-CBFs than for other concentric bracing configurations (namely diagonal and cross bracings). The research presented in this paper is aimed at revising the design rules and requirements provided for by EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The proposed design criteria are validated by means of nonlinear dynamic analyses performed on a study case. The results confirm the effectiveness of developed design procedure.