Month: March 2021

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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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