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The main motivation of current study is to present the results of an investigation conducted to obtain a relationship between damage index/damage level and residual displacement. SDOF systems with known lateral strength for periods ranging from 0.1 to 3.0 seconds are investigated for this purpose. Two hysteretic behaviours consisting of elastoplastic (non-degrading) and Modified Clough (degrading) models are assumed during analyses. A total of 140 ground motions including both far-field and near-field ground motions are considered in nonlinear dynamic time history analyses. A new damage index is proposed in terms of residual displacement, spectral displacement, maximum inelastic displacement and lateral strength. The comparison of proposed damage index with the analysis results is also presented.

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The study evaluates the seismic reliability of isolated multi-span continuous deck bridges considering the influence of the friction pendulum isolators and provides seismic reliability-based design abacuses as a function of both the structural properties and reliability level expected. The behavior of these systems is analyzed by employing five degrees of freedom accounting for five vibrational modes of the elastic reinforced concrete pier and a single degree of freedom to model the response of the infinitely rigid deck equipped with the isolators. The reinforced concrete abutment is modelled as a fixed support. The non-linear FPS response is described also considering the velocity-dependent behavior. The uncertainty in the seismic input is taken into account through a set of natural records with different characteristics scaled to increasing intensity levels. The uncertainty on the friction coefficient is modelled through an appropriate probability density function. Within an extensive parametric study developed for different isolator and system properties, fragility curves of both the pier and isolation system supporting the deck are evaluated. In line with the hazard curve of the reference site, the corresponding seismic reliability curves are computed by means of the convolution integral. Finally, seismic reliability-based design abacuses for different structural properties are proposed.

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In this research, cold formed steel sections have been used to reinforce and rectify the axial and shear performance of unstiffened, stiffened, L-shaped and T-shaped CFT columns. At first stage, Five L-shaped and Five T-shaped CFT columns, stiffened by various longitudinal internal steel plates and steel pipes subjected to axial and lateral loading, were numerically investigated. The variable study included the shape of CFT columns, various stiffening steel section, and the interaction between stiffening steel and concrete. Primarily FEM procedure had been verified with some available experimental results. The results indicate that the stiffening steel section have a great influence in the performance of L- and T- shaped CFT columns. Also, T-shaped CFT column shows the higher performance in terms of strength, stiffness and ductility than L-shaped section.
At second stage, the base model was CFT column as a benchmark specimen and three new and innovative type of CFT columns with difference in their longitudinal stiffening steel were investigated under axial and cyclic loading. The results show that reinforcement of CFT columns by this method, lead to enhancement in load carrying capacity, enhancement in lateral drift ratio, ductility, preventing of local buckling in steel wall, and enhancement in energy dissipation.

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Special and intermediate moment resisting frames are two main types of lateral load resisting systems used in high-seismic regions, depending on the height of the building. Current design codes consider only earthquake risks in the design of these structures and neglect subsequent hazards. The current study compares the multi-hazard robustness of these alternative designs for earthquake and subsequent fire. For this purpose, two special and intermediate four-bay four-story steel moment frames were designed and subjected to different earthquake intensities and fire scenarios. Three types of failures, including local failure (failure of beams), partial failure (failure in some elements but not the entire structure), and global failure (overall instability of the structure), were encountered in the analyzed models. It was observed that the intermediate frame had higher fire resistance against one-bay fire scenarios than the special frame. On the contrary, when the fire was considered in an entire story, the fire resistance of both models decreased considerably with increasing earthquake intensity.

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This paper is devoted to a brief presentation of the main results obtained within the FREEDAM research project. The project has been completed and, recently, also the dissemination of the results has reached the finish line. The project was devoted to the development of low-damage beam-to-column connections based on the use of friction dampers conceived to substitute the traditional dissipative zones of moment-resisting frames, i.e. the beam ends. The conception of these innovative connections is presented and the experimental tests carried out at the University of Salerno during the FREEDAM project are summarized dealing with the friction dampers, the beam-to-column joints sub-assemblages and the seismic simulation of a real scale one-bay two-storey building with the pseudo-dynamic testing method. Finally, the design procedures for seismic-resistant steel frames equipped with such connections are presented in the framework of Eurocode 8 and according to TPMC.

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FREEDAM connections consist of a symmetric friction device connecting the lower flange of the beam to the column by means of L-Stubs. This assembly prevents the damage of the connected members and dissipates energy by means of the slippage between the clamped steel elements and the friction pads of the device. In order to characterize the monotonic and cyclic performance of the joints equipped with friction dampers a comprehensive and extensive parametric finite element (FE) simulations have been carried. The FE models have been validated against the experimental results of the tests carried out within the FREEDAM project. The performed FE analyses allowed evaluating the response of both external and internal joints with the FREEDAM devices. In addition, different geometries of the friction dampers and the relevant beam-column assemblies have been investigated. The FE analyses confirmed the effectiveness of the design assumptions and the satisfactory performance of the investigated joints

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The high seismic performance of steel frame structures equipped with FREEDAM dissipative joints has been demonstrated through experimental and extensive numerical studies in the framework of a recent RFCS project. In particular, the performance of moment-resisting frames (MRFs) and dual concentrically braced frames (D-CBFs) was thoroughly investigated under seismic actions. Although the research has shown that such structures can dissipate the earthquake-induced energy with limited or even no damage, their robustness in case of accidental actions was not yet addressed. Hence, as required by the current version of Eurocodes, their ability to survive accidental events should be demonstrated. This paper presents the robustness assessment performed on 20 MRFs and D-CBFs under a Eurocode-compliant column loss scenario. In addition, analytical and numerical studies were conducted to demonstrate how the request for robustness influences the design of the joints initially tailored for seismic performances.

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In this work, the efficiency of four passive energy dissipation means, including viscous, viscoelastic, friction, and metallic yielding dampers, in high-rise building response was evaluated and compared. Conventional analyses and designs generally neglect the effects of soil and foundation flexibility. This effect is also considered in this study. First, a 20-story building with a steel moment frame was considered. Then, the nonlinear 2D model of this building is developed and subjected to nonlinear static pushover analysis to identify the floors that need a damper. The Response Reduction Theory method is used for this purpose. After designing each damper, four different models were replicated using viscous, frictional, metallic, and viscoelastic dampers. Each model was subjected to nonlinear dynamic analysis using ten far-fault ground motion records. The structural responses were extracted in the uncontrolled condition and in four controlled conditions with dampers. The results show that the metallic yielding and viscoelastic dampers have the best performance in reducing the structural responses than viscous and frictional dampers.

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