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Buckling-Restrained Braces (BRBs) have good ductility and sufficient energy dissipation capacity through inelastic behavior and are limited to a rigid connection. However, the global performance of Buckling-Restrained Braced Frames (BRBF) is subjected to local strength and ductility. In this paper, a ductile connection was applied to the BRBF to improve global performance. According to some reports on the good deformation capability of Reduced Beam Section (RBS) and Top-Flange Beam (TFB) splices rotatable hinge connections, the global ductility and structural performance of BRBFs with ductile connections can be improved. Therefore, we carried out our research on the relationship of global and local ductility of BRBF and analyzed the parameters, including three weak depths of RBS connections and two strength of inner cores of BRBs. Furthermore, we investigated the best approaches for calculating global seismic performance factors (response modification coefficient (R), overstrength factor (Ω₀), deflection amplification factor (C_d), and ductility reduction factors (R_μ)). We also evaluated the global seismic performance factors of BRBFs with ductile connections using the global structural ductility based on nonlinear static pushover analyses. The results can help establish global seismic performance factors of BRBFs with ductile connections.

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The evaluation of the correct seismic input represents one of the most important parameters for the design of structures, especially for those located in high seismicity areas. During last decades, several researchers have proposed different methods to obtain the seismic inputs considering also the large number of signals registration present within the different international databases. Despite these developments, some issues are still open, especially in presence of particular soil stratigraphy where the local seismic response analysis is required. Another important aspect that influence the seismic input evaluate at ground level is the presence of shallow underground structures, which change the signal trend on the surface. The paper presents the results of a sensitivity analysis referred to a shallow metro station embedded in granular soil. In particular, four different soil profiles, characterized by different value of  shear waves velocity, and five acceleration time histories, recorded during European seismic events, are considered, in order to obtain the amplification coefficients of the seismic signals evaluated on surface and due to the presence of the metro station.

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This paper presents a numerical model for the dynamic analysis of planar structures with seismic base isolation using a layer of stone pebbles. Following a brief presentation of the previously developed numerical model for structural analysis, the developed constitutive model for the stone pebble layer and the constitutive model for simulating the foundation-isolation layer coupling surface are presented. The model is based on a relatively small number of parameters, some of which were determined experimentally. The numerical model was verified by simulating the performed shake-table tests of simple structural models based on an aseismic layer of stone pebbles, and good agreement between the experimental and numerical results was observed. Finally, further verification and improvement of the presented constitutive models are outlined.

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Endurance Time (ET) method is a dynamic analysis in which the structures are subjected to a predefined intensifying acceleration. The inherently dynamic nature of ET makes it applicable for various types of structures with different heights and degrees of freedom. The purpose of this study is to investigate the feasibility of ET method for analyzing an isolated bridge under different controlled systems. The optimal control force is calculated using both the Linear Quadratic Regulator (LQR) algorithm and Continuous Sliding Mode Control (CSMC). To this end, a five-span isolated viaduct is selected as a case study. Column-isolator-deck system is idealized as a two-degree-of-freedom lumped mass model. Three distinct control strategies are used including active, semi-active, and passive control systems. The deck displacements obtained from ET method are compared against the results of conventional time history analysis for different excitation levels. The ET results show good accuracy in predicting the seismic behavior of isolated bridge under different controlled systems. On top of that, this method substantially reduces the computational demands contrary to time history analysis

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There are two point of views regarding the presence of beam web openings. The first attitude is treating the opening as non-intentional weakness imposed by non-structural necessities. The second and newly proposed attitude is to use these weakening parts as intentionally placed fuse elements to improve the seismic behaviour of the entire frame. In both cases, the existence of gravity loads on the beam causes an asymmetry in distribution of the internal forces of the beam when the frame is subjected to the lateral loads. This will cause, the different behaviour of the openings at two sides of the beam. This study evaluates the effects of gravity loads on the seismic behaviour of steel moment resisting frames with reduced web beams. For this purpose, two series of numerical models at beam and frame scales are developed and analysed under different levels of gravity loads. Based on the results, the unbalancing gravitational bending moment at the centre of openings causes the asymmetric yielding of the openings making one of the openings more critical.

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The seismic performance of steel frames can be efficiently evaluated via the Incremental Dynamic Analysis (IDA) approach. Generally, reference is made only to the transient interstory drift as a damage intensity measure (DM) but, as herein demonstrated, additional DMs could be suitably accounted for. The present paper is focused on the application of the IDA approach to Moment-Resisting (MR) steel frames by considering in total four DMs: the transient and the residual interstory drift, the residual load carrying capacity and the low-cycle fatigue of joints and members. The discussed numerical applications are related to four planar frames differing for beam-to-column connections and member cross-sections. Research outcomes underline how the additional information obtained from the proposed DMs contributes to provide a more accurate prediction of the effective post-earthquake performance than the one based on the sole transient interstory drift.

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The objective of this work is the study and the evaluation of the overstrength of short links in Eccentrically Braced Frames (EBFs) to be considered in the application of local hierarchy criteria. Starting from the results of experimental tests devoted to short links, linear multivariate regression is provided to evaluate the overstrength of links. The obtained mathematical relation accounts for the following geometrical and mechanical properties: the web slenderness of the link, the slenderness of the stiffening plates, the non-dimensional distance between the stiffening plates, the steel hardening, the non-dimensional length of the link and its ultimate rotation.  Moreover, to account for the uncertainty of the regression model and the material variability, the first-order reliability method (FORM) is applied to the limit state function, which is used to describe the local hierarchy criterion for short links based on the rigid-plastic analysis. So, the authors defined an overstrength factor accounting for the geometrical and mechanical properties of links and including a safety factor to account for uncertainties.

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In this research, Concentrically Braced Frames coupled with an elastic truss as a strong back system are analysed. The elastic system has the scope of reducing the permanent residual lateral displacement of steel frames subjected to strong ground motion. Responses of this system are compared with those of the buckling restrained braced frame without elastic truss. All members of the vertical truss, including the diagonal members, should remain in the elastic range during the earthquake, while other braces, that are buckling restrained braces (BRB), come into the plastic zone in severe earthquakes and provide the system with ductility and energy dissipation. Frames are initially designed according to current design codes and then the results are studied by nonlinear time history analysis subjected to the maximum considered earthquake level records and static nonlinear analysis. For the structures under study, the amount of residual inter-story drift ratio decreased on average from 1.33 percent to 0.58 percent, due to the use of an elastic truss in the BRB.

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