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This paper focuses on the assessment of the behaviour of Concrete Filled Steel Tube (CFST) columns with square/rectangular cross-section, made with Rubberized Concrete (RuC), under flexural loading. The study aims to evaluate the differences between this type of composite members and typical CFST members made with standard concrete (StdC), namely in terms of the influence of the rubber aggregate replacement ratio on member strength, ductility, and energy dissipation capacity. The experimental campaign comprised the testing of 16 square members, 12 RuCFST and 4 StdCFST, and 4 rectangular RuCFSTs. A number of parameters were investigated, namely the cross-section slenderness (i.e., the width-to-thickness ratio of the steel tube), the aggregate replacement ratio (i.e., the percentage of sand aggregate of the concrete mixture that is substituted by rubber particles), axial load level and lateral loading type. The test results are compared with the member capacities obtained with the application of Eurocode 4. The results show a minimal influence of the type of concrete infill on the monotonic and cyclic behaviour of the members and also allow concluding that the European code is conservative in predicting the capacity of the specimens. Furthermore, the results obtained demonstrate that the cross-section slenderness has an important role on the behaviour of these members. Nonetheless, the requirements pertaining this parameter that are currently defined in Eurocodes 4 and 8 can be relaxed. [ABSTRACT FROM AUTHOR]

According to EN 1998-1, chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility due to the interactions between the braces and intercepted beam. As a consequence, EN 1998-1 recommends values of the behaviour factor (namely q = 2 and q = 2.5 in ductility class medium and high, respectively) lower than that (i.e. q = 4) given for other concentric bracing configurations, e.g. both cross and single diagonal CBFs. The research activity presented in this paper is addressed to revise the design rules and requirements of EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The study is organized in two parts: in the first part design rules recently presented in literature are assessed, while in the second part new design criteria are proposed and validated against the results obtained from incremental dynamic analyses carried out on 2D frames extracted from low, medium and high rise buildings. [ABSTRACT FROM AUTHOR]

Chevron concentrically braced frames are one of the most cost-effective solutions for seismic resistant steel buildings. Therefore, this system is widely used in Europe and North America. Both European and North American codes adopt capacity design rules aiming at enforcing the dissipative behaviour into the braces and at preventing the damage in the remaining structural members. However, in order to achieve this purpose, European and North American codes recommend some different requirements and detailing rules, which substantially influence the overall performance and energy dissipation capacity. The research presented in this paper is addressed (i) to verify the effectiveness of the design requirements prescribed by Eurocode 8 (EC8) compared to North American codes (i.e. both AISC 341 and CSA-S16), (ii) to identify the criticisms of EC8 needing revision and upgrading. In order to achieve these objectives, a comprehensive parametric numerical study based on nonlinear dynamic analyses is carried out. 2D frames extracted from low, medium and high-rise buildings are analysed and the main structural parameters affecting the performance against lateral loads are described and discussed. The critical review of the examined standards and the discussion of numerical results highlight that the design rules given by North American codes are more effective than those recommended by the current version of EC8. In particular, EC8-compliant frames show the poorest energy dissipation capacity with tension bracing members almost in elastic range and severe demand on those in compression. On the contrary, both CSA- and AISC-compliant cases exhibit satisfactory energy dissipation capacity. [ABSTRACT FROM AUTHOR]

One issue of major importance regarding the application of seismic assessment guidelines is that of the deformation capacity limits prescribed for the various limit states. In the case of existing steel structures, Part 3 of Eurocode 8 (EC8-3) defines the limits in terms of plastic rotations, which are only applicable to cases where normalized axial load levels are lower than 0.3 and to cross-section classes of type 1 and 2. These limits resemble the ones defined in ASCE 41, suggesting a direct reproduction from the latter document despite their derivation on the basis of typical American profiles. Hence, this paper aims at evaluating the deformation capacity of European steel members and to answer the question of how adequate are the current EC8-3 limits. Based on detailed FE models, the influence of member imperfections, axial load and real ground motion records is assessed. Fracture due to ultra-low cycle fatigue is taken into account and general expressions for predicting the rotation capacity of a wide number of European cross-section profiles are proposed. [ABSTRACT FROM AUTHOR]

The paper validates Ω* method proposed by some of the authors in previous papers for design of X-Concentric Braced Frames (X-CBFs). This method was obtained relaxing some of the requirements of the method provided by the European seismic code (Eurocode 8, EC8). Therefore, Ω* method is conceptually similar to that of EC8, which makes it easy to be incorporated into EC8 and to be embraced by the European structural designers. The paper analyses the seismic performance of a set of X-CBFs designed both according to EC8 and Ω* methods. Several buildings characterised by different numbers of storeys, numbers of bracings in plan and by different bay spans are considered. Non-linear dynamic analyses have been carried out by the computer code CLAP to evaluate the seismic performance of the analysed buildings. The results of the numerical analyses show that the Ω* method: (i) reduces the unnecessary global overstrength which typically is found in structures designed in accordance to EC8 design rules; (ii) leads to an optimized structural design; (iii) ensures a local and global ductility of braces under cyclic actions comparable to EC8 design solutions; (iv) has a greater “flexibility” in the design process. [ABSTRACT FROM AUTHOR]

This article focuses on the likelihood of the weak storey behaviour and the weak storey collapse of diagonally concentrically braced frames designed according to Eurocode 8 provisions. The emphasis is primarily put on the nature and development of the weak storey behaviour in order to designate the effects that shall be taken into account in an effective design procedure. In a second stage, the focus is on developing supplementary conditions to Eurocode 8 based on plastic analysis that can enhance the designs by preventing the occurrence of weak storeys. [ABSTRACT FROM AUTHOR]

Dealing with steel moment resisting frames (MRFs), the latest version of Eurocode 8 allows us to dissipate the seismic input energy in connections provided that their characteristics under cyclic loads are certified by means of experimental testing. Within the beam-to-column joint typologies to be used in seismic resistant steel frames, the double split tee joint (DST) represents an interesting solution due to its easy fabrication and repair after a destructive seismic event. Nevertheless, the cyclic behavior of this joint typology is usually characterized by pinching and strength degradation phenomena due to the plastic engagement of the rectangular T-stubs which compromises the use of DST joints as dissipative elements. Within this framework, in this paper, in order to improve the hysteretic behavior of this connection typology, a new type of dissipative DST joint is presented. In particular, the proposed dissipative T-stub is designed substituting the rectangular T-stubs with the so-called X-shaped T-stubs, whose flange plates are cut into an hourglass shape similar to that of ADAS dampers. In particular, in the paper, a model that is able to predict the resistance of the proposed X-shaped T-stubs accounting for moment–shear interaction is developed and rules for designing the optimum shape of dissipative DST joints are proposed. Finally, the results of an experimental activity on real scale joints are presented aiming to verify the reliability of the proposed design approach and to compare the cyclic behavior of classical and X-shaped DST joints evidencing the benefits provided by the proposed dissipative joint. [ABSTRACT FROM AUTHOR]

In seismic design of steel structures, the "dual-steel" concept concerns the combined use of High Strength Steel (HSS) in non-dissipative members and Mild Carbon Steel (MCS) in dissipative zones, in order to control the global frame behavior into a ductile overall failure mode. In this paper, a comprehensive parametric study devoted to investigate the seismic design and performance of Eurocode 8 compliant dual-steel Moment-Resisting Frames (MRF) is presented and discussed. The overall seismic performance has been analysed through static and dynamic nonlinear analyses against three limit states: damage limitation (DL), severe damage (SL) and near collapse (NC). The investigated parameters cover both geometric and mechanical variables, as the type columns, span length, number of storeys and spectral shape. The analyses showed that the use of HSS in Eurocode 8 compliant MRFs is effective to provide overall ductile mechanism, but it may lead to inefficient and uneconomical structures characterized by limited plastic demand due to the large design overstrength. The comparison between dual steel MRFs with those entirely made of MCS showed that: i) in order to fulfil the codified drift requirements and to limit the stability coefficients, the same shapes for members should be used for both structures in the most of cases; ii) a similar performance can be recognized in both dual steel and single grade steel structures under both damage limitation and significant damage limit state; and iii) dual steel frames guarantee a better control of plastic mechanism than single grade steel frames at near collapse limit state. [ABSTRACT FROM AUTHOR]