Month: September 2019

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To investigate the contribution of the beam-column connection on the anti-collapse capacity of the steel frame structures, on base of the the experimental and analytical studies of predecessors, the numerical simulations with simplification for the joints are presented. The nonlinear static and dynamic analysis methods are employed to assess the anti-collapse capacity of the structures under the column removal scenario. The related researches are developed from three aspects including the vertical displacement above the failure column, the beam axial force and the dynamic increased factor. The allowable rotation angle of steel beam in GSA and the test-based ultimate plastic strain of steel are considered as the collapse criterions. The results show that the the anti-collapse capacity of the structure attaching damper joints is considerable. And the damper in the connection possesses good damping effect. Finally, based on the energy balance method, a DIF-based limitation for assessing whether the structural collapse occurs or not is found, and a simple method for comparing the anti-collapse capacities of different structural systems is proposed.

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This paper explores the capabilities of a superelastic, tensegrity-inspired bracing system acting as a seismic protection device. The metamaterial-type response of the proposed structure, which is related to its geometry more than to the nature of the employed materials, yields a passive control device with optimized structural response. It operates as a lightweight mechanical amplifier for longitudinal displacements. The enhanced energy dissipation and the re-centering capacity of the proposed tensegrity-SMA braces are demonstrated through experimental tests, and the seismic analysis of a benchmark structure. The effective performance of the proposed bracing in reducing the seismic damage of the served building paves the way to the design of novel seismic energy dissipation devices that combine tensegity and superelasticity concepts.

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This paper describes the experimental quasi-static tests performed at the structural laboratory of the University of Basilicata on hysteretic dissipative dampers consisting of U-shaped steel plates (U-shaped Flexural Plate) to be used for dissipative bracing systems.
The cyclic tests, are preparatory for shaking table testing of a 3D, 2/3rd scaled, three-storey post-tensioned timber framed building equipped with dissipative bracing systems composed by V-inverted timber rods and two UFPs in series, designed for each storey to yield in a controlled manner.
In order to optimize the design procedure of the UFP dampers, the analytical models available in the literature for the definition of the elastic stiffness and yield force of the devices are compared with the results of quasi-static experimental tests. Furthermore, in order to verify the robustness of the seismic protection technique, a parametric analysis is carried out considering non-linear numerical models, varying the characteristics of the dissipative bracing design parameters. Finally, the preliminary results of the shaking table tests on the braced structure are compared with those of the bare structure in order to validate the effectiveness of the dampers in the control of the seismic response.

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An advanced seismic retrofit strategy of industrial buildings with reinforced concrete structure is presented in this article. It consists in seismically isolating the roof and installing fluid viscous dampers at the roof girder-to-column joints, in the girder vertical plan, and at the ends of the longitudinal beams linking the column top sections, in the orthogonal direction. A retrofit solution based on this strategy is demonstratively designed for a representative case study, i.e. a single storey double hall-type prefab structure built in the late 1980s. A synthesis of the results of the analyses carried out in current conditions is offered, which highlights near-collapse conditions at the maximum considered earthquake level. The response in retrofitted conditions results to be safe and undamaged up to the same seismic action level, thanks to the high damping capacity of the dissipative joints. The structural installation details of the protective system are illustrated, along with technological details of the pipes crossing the isolated roof plan.

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The load bearing capacity, global ductility and overall stability of steel frame can be improved significantly through the use of buckling-restrained braces (BRBs). Based on the open resource platform OpenSees, finite element models of two types of steel frame buildings, one is nine story steel frame (SF) building and another is buckling-restrained braced steel frames (BRBFs) buildings are developed. The structures were analyzed using both deterministic and probability analysis approach. No component-removal random incremental dynamic analysis (IDA) and component-removal random IDA are used to analyze collapse resistance of the buildings under seismic load. The collapse modes of SF and BRBFs under earthquakes are discovered. The nonlinear dynamic responses of SF and BRBFs are analyzed before and after the removal of certain critical components using the alternative path method (APM) approach stipulated by GSA and vertical IDA method respectively. Correspondently, the probabilistic fragility function of collapse likelihood of SF and BRBFs are also derived based on random vertical incremental dynamics analysis approach. The analytical results show that the use of buckling-restrained braces ensures alternative load path, therefore changes the failure modes and improve collapse resistance of structures.

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In order to obtain a full serviceability of base isolated structures after earthquakes, the curved surfaces sliders based isolation systems should have a sufficient recentring capability to avoid large residual displacements and their accumulation. The residual displacement estimations are expressed as function of the isolator properties (effective radius and friction coefficient) and of the characteristics of the ground motion (maximum displacement). The current seismic codes use different empirical approaches about the recentring capability requirements and for the expected residual displacements. Moreover, their evaluation can be done with sufficient accuracy only through complex numerical nonlinear time-history analysis. In this paper, the recentring capability of Curved Surface Sliders is discussed on the base of the main results of recent experimental studies and on the codes requirements. Moreover, a simple design tool for the estimation of the permanent residual displacement of the curved surface isolation systems is proposed as function only of the isolators properties.

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Passively controlled structural systems may be exhibiting scarce capability in resisting dynamic solicitations under adverse special or unexpected conditions. Improvements of the overall performance of the passive system may be obtained when introducing additional control devices, possibly coupling different technologic solutions and moving to mixed systems. In the paper the performance of a base isolation system is increased by embedding in the control layout an additional passive/active device, commanded by a newly designed control algorithm  .

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